How would one go about determining the position of the different planets in our solar system with respect to the celestial sphere based on the following data set? Is there a practical way to calculate this?
SUN
ra - 09h 00m
dec - 17.2
MOON
ra - 09h 11m
dec - 11.3
MERCURY
ra - 09h 33m
dec - 16.3
VENUS
ra - 06h 19m
dec - 22.8
MARS
ra - 09h 43m
dec - 15
JUPITER
ra - 12h 27m
dec - -1.7
SATURN
ra - 05h 46m
dec - 23.1
Any suggestions would be awesome!
Here's my answer. I'll try to make it as comprehensive as possible.
It's pretty hard to define the edge of the Solar System. Most people would probably define it as where objects are no longer gravitationally bound to the Sun. That just shifts the question a little, though: Where is that dividing line? To try to answer this, I'll go over the regions of the Solar System.
The first region is the domain of the inner planets - basically everything from the asteroid belt inwards. It is comprised of Mars, Earth, Venus, Mercury, their moons, and all the smaller objects that surround them. The inner Solar System is very rocky, as one can imagine. The terrestrial planets are primarily made of rock, as are the asteroids and the inner planets' moons.
The second region is the domain of the gas giants. It consists of Jupiter, Saturn, Uranus, Neptune, their moons, ring systems, and assorted smaller bodies, such as Trojan asteroids. The gas giants had a big influence on the Solar System when it was first formed, pulling in chunks of rocks, grabbing moons, and possibly stabilizing or de-stabilizing orbits. Some may have migrated outwards (as per the Nice model), but their orbits are currently stable. The gas giants are made largely of gases, but it is thought they have solid or molten cores. The composition of their moons is familiar - more like objects in the inner Solar System.
Next up is the Kuiper Belt. It's sometimes introduced as a cousin of the asteroid belt, but that's not accurate. The bodies that make up the Kuiper Belt are chunks of rock and ice. Notable examples of Kuiper Belt bodies and/or trans-Neptunian objects are the dwarf planets Pluto, Sedna, Makemake and Haumea. There are also lots of smaller objects, including some short-period comets (although these are more properly part of the lesser-known "scattered disk"). While there have been theories for years about another planet out there, it is not considered likely. The Belt extends from 30 to 50 AU.
Further out still is the Oort Cloud, named after Jan Oort. Observations of objects in the Oort Cloud are extremely difficult, if not impossible, so its existence has not yet been verified. It is populated by long-period comets and smaller objects. These are also composed of rock and ice. The Oort Cloud is thought to extend up to an incredible 50,000 AU. While the other regions so far mentioned are roughly in planes, the Oort Cloud is spherical.
Some consider the far edge Oort Cloud to be the edge of the Solar System, because the majority of the mass of the Solar System is within it, but the boundary between the Solar System and interstellar space is actually thought to be within its inner reaches: the heliopause. This is generally accepted as the Solar System's boundary because it is where the solar wind meets the interstellar medium. This is often placed at 121 AU - which is where Voyager 1 passed through in 2013. The heliopause is the far boundary of the heliosphere, beyond which the interstellar medium takes control. Inside "layers" are bounded by the termination shock and the heliosheath.
In summary, while the Solar System is made of many regions, the heliopause is considered to be its outer boundary.
Once again, I welcome any and all input regarding this question and answer.
Is it the paper David H pointed out, by Geringer-Sameth et al. (2015)? If so, then I should point out that they're not the first. Just using Wikipedia, I came across Weniger (2012) and Albert et al. (2008).
Geringer-Sameth et al.'s abstract reads (in part)
We present a search for gamma-ray emission from the direction of the newly discovered dwarf galaxy Reticulum 2. . . . Reticulum 2 has the most significant gamma-ray signal of any known dwarf galaxy. If Reticulum 2 has a dark matter halo that is similar to those inferred for other nearby dwarfs, the signal is consistent with the s-wave relic abundance cross section for annihilation.
Albert et al. also studied a dwarf galaxy:
The nearby dwarf spheroidal galaxy Draco, with its high mass to light ratio, is one of the most auspicious targets for indirect dark matter (DM) searches. Annihilation of hypothetical DM particles can result in high-energy γ-rays, e.g., from neutralino annihilation in the supersymmetric framework. A search for a possible DM signal originating from Draco was performed with the MAGIC telescope during 2007.
The point is, this has been done before. These folks aren't the first.
Has someone actually detected gamma rays emitted by neutralino (or any other dark matter) annihilation?
More analysis is probably needed. I'll quote the paper itself:
While Ret2's X-ray signal is tantalizing, it would be premature to conclude it has a dark matter origin. Among alternative explanations, perhaps the most
mundane is the possibility that an extragalactic source lies in the same direction. Searching the BZCAT [54] and CRATES [55] catalogs reveals a CRATES quasar (J033553-543026) that is 0:46 from Ret2. Further work must be done to determine whether this particular source contributes to the emission, though we note that at spectrum radio quasars rarely have a spectral index less than 2 [56]. One of the much-discussed astrophysical explanations for the apparent Galactic Center excess is millisecond pulsars [24, 26, 57{61]. In the case of Ret2, it is the high-energy behavior which disfavors a pulsar model, as millisecond pulsars exhibit an exponential cut-offat around 2.5 to 4 GeV [26, 30, 61{64]. Alternatively, high-energy cosmic ray production could potentially arise in the vicinity of young massive stars. Upcoming photo-metric and spectroscopic analysis of Ret2 will check this possibility.
Don't jump to conclusions. They didn't. It stinks, but the answer to your question is, "Nobody's sure."
I need to upgrade my tripod legs.
Yes, this seems to be the case
I don't need to upgrade the head, since it's rated to twice the capacity of the legs, and to twice the weight of the biggest binoculars I'll use.
Seems right to me. However, if you have some money to spare, I think you should consider investing in a Parallelogram Mount (P-mount). These usually look like long arms with counterweights and a place to attach your bino. They make it easier to adjust the height, observe objects close to zenith and are usable from a chair.
I should look for legs that are rated to twice the weight of the biggest binoculars I'll use.
I don't have this problem with binoculars as the ones I own are pretty light but with photographic equipment, I try not to exceed half the declared capacity. The better the brand, the closer you can get, I suppose.
I should look for a set of wooden legs, since these have greater stability than aluminium legs while being affordable, unlike carbon fiber.
I've used wooden legs for a small telescope and I wouldn't like to do it again. Unless you're only planning to use a tripod around the house. Wooden tripods are usually heavy, clunky and not very portable.
Carbon fiber tripods, on the other hand, tend to be very light so you'll have to be a little more careful with a big and heavy bino than in case of an aluminium or wooden one. If you get one, make sure it has a hook under the column, on which you can hang something to shift the center of mass closer to the ground.
I once had a carbon tripod almost tip over after a strong gust of wind when I had a large-ish telephoto lens mounted on it. Managed to catch it just in the nick of time.
I don't think applying Earth data to Mars makes much sense, well, except perhaps at the very beginning. The reason I say that is that life on Earth took a long time to get what we might consider "interesting", for lack of a better word.
Source - and, OK, it's a children's book, but I like the picture.
4 billion years ago - simple cells.
3.5 billion years ago - photosynthesis.
2 billion years ago - cells with Nuclei
1 billion years ago - bacteria.
So the Earth took 3 billion years to make - bacteria. Granted it's only one planet as a sample, but if that's standard, then, arguably, most of the life in the solar system might be 1 celled and, you know, kind of boring to you and me, though I'm sure scientists would love to study 1 celled organisms from other planets.
If planets need a few billion years before things like plants, fish, insects, etc, evolve, then many planets won't stay in the Goldilocks zone that long. . . . or, option B, maybe things happened slower on earth than other planets, but for now, we just don't know. Finding life on Mars or records of past life, if there was any, could help answer some of those questions.
Mars may have lost it's oceans fairly quickly, in less than a billion years. That's not a long time for life to evolve, at least based on the Earth Model.
Now, low gravity, probably not a big deal. Animals and trees on a low-G planet grow grow taller and thinner/weaker - thinner bones, smaller muscles for example. High-G, just the opposite. Shorter and stronger with thicker bones. Prior to lungs, Insect size is determined by Oxygen content in the atmosphere much more than gravity. (Fish-Fin size point removed as it probably wasn't correct).
Probably none of this happened on Mars cause I doubt life evolved that far but in theory on a low G planet you might get very large animals, perhaps the size of 10 story buildings, because size is a good evolutionary defense mechanism. (Fun to think about, right?)
Thin Air, that's a bigger problem cause thin air leads to evaporating oceans and once the oceans evaporate, life would have a hard time continuing the evolutionary process Life needs water, at least here on Earth. Life can adapt to living with small amounts of water but life needs water. In ice, primitive Life hibernates, but it doesn't continue to evolve.
Now it's possible that Mars' thinning atmosphere coincided with it cooling off and it could have had oceans frozen at the top but liquid below that for some time, while heat from inside the planet maintained liquid water and life was able to survive in that. This happened to the Earth, when the Earth was covered by ice during the snowball earth period and when Snowball Earth ended, the Cambrian explosion started. The problem on Mars was, if Mars had a snowball with liquid water below the ice period, it never ended. It never went back to liquid oceans and that's a problem for evolution.
It's possible that snowball earth (limiting the sunlight and atmospheric gases available to life inside the ocean) forced bacteria to evolve, hunting for food rather than simply absorbing it via sunlight and air, but that's just speculation on my part but the timing was pretty consistent. The Cambrian explosion followed snowball earth.
Humanoids on other planets (assuming we ever find any) would probably have characteristics adapted to that planet. We stand upright because our ancestors found it helpful to run. That might not be the case on other planets, perhaps that have thicker brush and no open planes. That's just one example, there's probably others. Our height likely developed out of the optimal height for hunting. If we just were gatherers and trappers, not spear throwers we might be quite a bit smaller with shorter arms cause there's be no evolutionary advantage to being bigger or longer arms if we climbed trees to get away from predators. You can clime trees higher if you're small for example and be safe that way. Humanoids might have tails on other planets if they had a use for them, like, impressing the opposite sex with them or for balance for tree swinging/jumping. There's a variety of possibilities that go way beyond gravity (which might just have an effect on body size and shape) or air pressure, which might affect things like wings for gliding, running (as thick air might reduce running speed) and lung size.
On red dwarf planets for example, plants and people might be significantly different colors. Plants might be blue or black, to absorb more red light, Animals, for example, might have colors into the Infra-red spectrum that we don't see. One blue sun planets, plants could be red and animals might have colors into the UV spectrum. (Some birds on earth have UV spectrum colors that we don't see but they do). Thicker air pressure might affect sound as well, they might talk much quieter perhaps higher pitch and have smaller vocal cords and smaller ears, where as, thinner air, bigger animals might make thunderous yells when they communicate.
There's a variety of possible factors. . . . hope I haven't gone too deep into speculation here, but speculation is fun sometimes.
Personally, I don't believe Mars ever came close to any of the ideas I mentioned above. I don't see how it could. it wasn't habitable for long enough.
Does this mean that pre-Earth was roughly 9 Moon masses (~10%) lighter
than today's Earth? Or could much mass have been ejected from the
Earth-Moon system?
I think that's likely about right. In a nutshell, there's two basic questions here. How much mass was lost as a result of the giant impact and how much mass was gained after the giant impact during the late heavy bombardment and following collisions.
We know that smaller bombardments on Mars has resulted in debris landing on Earth, so it seems highly likely that some debris was lost when Theia and Earth collided, but estimating how much is tricky and you'd really need to be well versed in the models to have a pretty good guess.
One theory is that Theia formed in an Earth Trojan point so it shared the same orbit around the sun that the Earth did. Source This would cause a slower impact than a more oblique approach where the velocity of impact wouldn't be much greater than the Escape Velocity of Earth. If the impact velocity is only a bit above the necessary escape velocity and if a fair bit of energy is transferred into orbital momentum and heat, it's unlikely that a high percentage of debris would reach escape.
Now if it was a faster impact from a more oblique orbital approach or a head on collision that would create greater compession and rebound, those two scenarios would likely lead to more material escaping. I can't give you precise numbers, this is more of general thinking about what might happen.
Again, according to Wikipedia about 20% of the mass of Theia entered the earth's orbit after the impact. Orbital Velocity has to be at least Escape Velocity over the square root of 2 and less than escape velocity. Source
So if we use 11 KM/s as an escape velocity estimate, anything that flew off the impact at less than 7.5 KM/s would have returned to Earth pretty quickly. A bit above 7.5 and maybe about 9 or so KM/s would be low Earth orbit and about 10 KM/s high earth, with 11 KM/s, likely escape and enter in a near earth orbit around the sun. You'd need a bit faster than that to have a truly outside of earth orbit.
What percentage of Theia flew off at those velocities is hard to say, but I think it's likely that much of the planet slowed down upon impact and not too much escaped the Earth's Hill sphere, but I'd be guessing if I tried to put percentages to that.
Did the impact substantially and immediately change Earth's orbit,
such as its average distance from the Sun?
Because it was a (I assume) a Trojan object, the 2 young planets would have shared the same orbit and so there probably wouldn't have been a big change. Orbital momentum should be largely be conserved though some orbital velocity might be converted to rotational momentum, I don't think there would be a huge change. Similarly, if any debris from the impact flew off in one particular direction, the remaining material would react with similar momentum in the opposite direction, but having much greater mass, the effect would be small.
Certainly some orbital change probably happened, but compared to the entire Earth, it was probably small.
Now, if the impact was different than theorized, that might change the answers quite a bit. (My 2 cents anyway)
There can be stars (and small star systems). Stars need not be found only in galaxies.
There can be gas clouds.
Most nebulae are in intergalactic space. Indeed, for a while, both galaxies and nebulae were termed as "nebulae" until the differing nature of galaxies was discovered.
Almost any (small) structure that can be present in a galaxy can be present in intergalactic space, for that matter. Black holes (neutron stars, white dwarfs, brown dwarfs, ... ), star clusters, star systems, etc can all be present.
Finally, there's a very rare (rare in the density sense) plasma, mainly of hydrogen, that makes up almost all of the intergalactic medium. Zero pressure is an unattainable ideal case.
The combination of the conservation of angular momentum and gravity give you the inclination and direction. Gravity will condense material in the axis direction of the angular momentum, and collisions and gravitational interactions will damp oscillations in that direction, forming a disk of material. The angular momentum resists gravity in the plane perpendicular to the axis, maintaining the extent of the disk. Over time, the direction of rotation of the angular momentum is the direction of the vast majority of the material, due to collisions and interactions with that smaller population going the wrong way on a one-way street.
The circularity of the orbits is the result of a more dynamical process. Hopefully someone else here can explain it better than the following. My simplistic understanding is that a bunch of orbits crossing each other is not stable. Planets and planetesimals have their orbits changed continuously until such time as they settle into orbits that have fewer interactions with other bodies. Sort of a natural selection. In the long haul, this results in a relatively stable configuration with circular zones that tend to not interfere with the other circular zones. In fact, this is now part of the definition of the word "planet", in that to be called such, a planet needs to clear the neighborhood of its orbit. Though its not clear how it could occur, a bunch of elliptical zones that happen to be co-aligned would also not be stable since orbits precess due to various influences.
Where the material was less dense than where the planets are currently must certainly have many objects in eccentric, retrograde, and/or highly inclined orbits. Pluto is the first hint at that, with a relatively high inclination and eccentricity compared to the planets. Sedna is far more eccentric.
As for other systems, I'm sure there must be some oddballs out there. However the Kepler mission has observed mostly circular orbits for planets around other stars.
I was looking at Arcturus with a pair of binoculars, and noticed that when they vibrate due to my heartbeat, Arcturus seemed to move differently than the other dimmer stars.
I started playing with that visual effect and noticed that it happens both vertically and horizontally, and that I could even make it "overlap" with a nearby star. It is like it either lags or is ahead of the others in terms of how it moves in the field of view as the binoculars do their slight shake. Why is that?
The first thing to consider is that the area of a beam will, over long distances, diffuse. The best situation we can hope for is a diffraction-limited system, where this diffusion is minimized thus maximizing our received signal. That is, in theory we have a perfectly collimated transmission beam that neither diverges nor converges.
In practice, we are still limited by diffraction. A diffraction limited system is described by the formula
$$ sintheta = frac{1.22lambda}{D}, $$
which prescribes an angular resolution $theta$ in terms of wavelength $lambda$ and a circular aperture of diameter $D$. This is called the Rayleigh criterion. The definition of angular resolution, in this case, is when two point sources are just discernable from each other where the principal maximum of the airy disk pattern of one source coincides with the first minimum of another. It's this definition that results in the apparently arbitrary constant of $1.22$.
We usually think of diffraction being applicable in terms of receiving a signal - for example, a space telescope will usually have a diffraction-limited optical system. However, the exact same laws hold true whether we are receiving or sending a signal. The optical path is the same. Everything is just in reverse!
Side note: if we instead projected an image into space, in order to acceptably resolve the image a receiver would need to have an angular resolution equal to, or greater than, than the projection. This includes a spatial resolution criterion in addition to the signal-to-noise performance discussed below.
To make a real-life example, let's consider a radio signal. Since a distant receiver will be getting a frequency-modulated signal not unlike FM radio, we are not concerned with angular resolution. We don't care if the "image" is blurred, or even if some areas of the originally transmitted beam entirely miss our receiver. All we are concerned with is the modulation of frequency over time - it's a one-dimesional signal.
In this case, a receiver is a noise-limited system. This NASA report outlines some of the limitations that a realistic implementation of interstellar communication must deal with. Even in the case of a quantum noise-limited system, we can still make the best of the limitations dealt to us.
If the signal-to-noise ratio is above an acceptable threshold then the signal will be received well. There are so many factors to consider that really only an order-of-magnitude estimate is feasible. I don't know enough about this to come up with a good estimate myself of the noise levels of a particular system.
Project Cyclops (1971) was the initial investigation into the feasibility of a search for extraterrestrial intelligence. For example, on page 41, we can see that the minimum noise temperature of a receiver receiving the 2.4 GHz Arecibo message is about 4K - the major contributor to noise here is the CMB. Frequencies of this order of magnitude will usually provide the best possible noise performance - too high and quantum noise and atmospheric effects become significant. Too low, and galactic noise takes over.
This noise temperature provides a noise floor for the signal. The receiver usually introduces a significant noise temperature to the degree of some tens or hundreds of Kelvin, so any practical limitations on interstellar communication tend to become a function of our equipment.
Although the Arecibo message was broadcast at a good frequency, for very long-distance communication amplitude modulation is superior to frequency modulation as it's easy to increase the pulse duration and interval to compensate for a weaker signal strength.
This table from page 50 of the well-worth-reading Cyclops report shows that a single $100~ mathrm{m}$ transmitter/receiver combination, with a transmission power of $10^5~mathrm{W}$, could function at a distance of 500 light years.
Building bigger transmitters and receivers will increase the maximum distance of communications. So will increasing the transmission power, pulse duration, and pulse interval. Current technology could let us communicate over tens or hundreds of light years. To communicate further, just build something bigger. The laws of physics place few limits on the distance we can communicate.
What a nightmare - there is no accepted definition.
A common method is to use the fraction of the night (between the times of astronomical twilight) that the moon spends above the horizon. The problem is that this does not correlate perfectly with fractional lunar illumination or sky brightness. It does provide a good method of deciding when a night is "dark", but you get a bit of a mixed bag of "grey" nights.
It is found that the sky brightness is pretty much determined by fractional lunar illumination (FLI - the fraction of the moon's visible hemisphere illuminated by the Sun) once it exceeds about 0.15; so this is the definition that is currently used at the Isaac Newton Group of Telescopes.
Dark $0leq$ FLI $<0.25$; Grey $0.25leq$ FLI $<0.65$; Bright $0.65 leq$ FLI $leq 1$, where the FLI is calculated at 0h UT (close to midnight at the ING).
See http://www.ing.iac.es/PR/newsletter/news6/tel1.html for further discussion (in which I only just noticed I got a mention in the acknowledgements ;) ).
67P/Churyumov–Gerasimenko has a highly irregular dumbbell shape. But the sample of comet shapes observed is very small, so I wonder if irregular shape is the norm for comets and for small moons. Many known moons are no larger than this ~4 km diameter comet. The smallest moons imaged are modestly irregular, basically just elongated, at least they don't have a waist like 67/P. The most elongated moon is perhaps ~135/60 km Prometheus.
Is there reason to believe that moons which are too small for hydrostatic equilibrium get more rounded than comets of similar mass and composition? Moons differ from comets in several ways. AFAIK: Moons in general have a very different gravitational environment, a much more stable distance to the Sun, experience more frequent impacts, another formation history if not captured. Composition and density depends on the formation distance from the Sun, although even ~300 km Hyperion has a similar density as 67/P.
Should we expect the small moons in general, and the moons of Pluto especially, to be rounded or dumbbell shaped? If 67P is a merged binary, isn't it more likely for two objects to merge if they are moons instead of comets, since neighboring moons have low relative speed? ~100-200 km Janus and Epimetheus look as if they could merge fairly calmly. Does the lack of (observed) dumbbell shaped moons tell us something about 67P, that its shape is a rare outlier for example?
How do professional astronomers measure and describe (ambient) observation conditions?
I know smog, light contamination from the city lights, fog, clouds, rain/snow, humidity etc all contribute negatively to quality of the image, obscuring the celestial objects more or less, but I'm fairly sure there is a more precise measurements of viewing capability for any given location or time than "good weather and far from cities" or "Kinda can see M42 in Orion if you squint."
Optical refraction is related to the change in direction of a light ray when the refractive index changes. Excluding Earth's atmospheres and instruments, I think that refraction has little/no impact in astronomy.
The only cases that comes to my mind where we can (probably) have some important refraction is in eclipsing star binaries or near edge on planetary systems.
Let's imagine a planet transiting behind his star. Some of it's light passes through the stellar atmosphere and gets refracted. As the atmosphere is curved and likely changes the refractive index with height, it acts like a lens dispersing (intuition says so) the planet light.
Edit A similar description holds in general for any object passing behind an other one that have atmosphere.
And there is Gravitational Lensing (if you allow me), which has much larger impact on observations. This is caused by gravity bending light rays when passing near galaxies/cluster of galaxies(/stars/...). One of the differences of gravitational lensing with respect to standard lenses is that there is no change in refractive index, so it's achromatic (all wavelengths get bent by the same angle).
The effective index of refraction can be described as ( source: Narayan and Bartelmann(pdf) ):
$$ n = 1 + frac{2}{c^{2}} |Phi|$$
where $Phi$ is the gravitational potential and is generally a function of position of the object.
Gravitational lensing is canonically divided in three groups:
Strong lensing, usually observed in galaxy clusters or around massive galaxies. The gravitational potential is so strong that the the image of a background galaxy is heavily distorted into arcs and rings, like in this striking image of Abell 2218 from HST:
Weak lensing. The light of a galaxy encounters matter (and a lot of dark matter) travelling to us and gets refracted. This doesn't have a dramatic effect as in strong lensing, but distorts the shape of the galaxy. And this distortion can be used to study, e.g., the dark matter distribution around some object or the content of the universe.
Micro lensing. Imagine to observe a star and somehow know that a blob of dark matter is going to pass in front of the star. The blob is not big enough to distort the star shape, but for sure it will increase by a small amount the luminosity of the star.
I haven't managed to formulate a coherent single answer, but here are several suggestions for where to find some hints of current topical research where you might be able to contribute.
Astronomy is increasingly using large open source projects, many written in Python, which itself free. For example, the Astropy project is trying to create an extensive Python library for astronomical data manipulation, so you could try to contribute some of the desired features in a project like that. (There are other, more substantial, projects, especially in various kinds of modelling, but they require an understanding of the physics and are often big chunks of code, written in Fortran.)
If possible, I'd suggest looking at review articles (e.g. in Annual Reviews in Astronomy & Astrophysics). Though many of the articles are probably behind paywalls, most of the recent ones should also be available on the arXiv. Similarly, you can also try searching arXiv for lecture notes from summer/winter schools.
In a similar vein to contacting people, you might find that potential projects are listed online, in which case you'll see what kinds of things people would like to do. For example, so quick Googling netted me information at Manchester, St Andrews, QMUL, and UCL. (Clearly Google thinks I'm in the UK...) While it probably doesn't make sense to actually try to carry out these projects, they might give you a better idea of the sorts of things that need doing.
I'd particularly watch out for anything that involves data-mining, since that mostly involves spending time crunching some of the huge datasets available. I'm mostly aware of projects in the time domain (e.g. OGLE and WASP) but there are also larger projects like SDSS that I think have more data than people to sift (intelligently!) through it all.
I'd note here the special cases of Kepler and it's continuation K2. In these cases the actual analysis of the cameras' pixel data is still an open question, especially for K2. Any clever progress on automatically reducing the data better would be a boon in that field, although several active research groups are also working on it full time.
Note to future answerers: We have been working in the Astronomy.SE main chat room with OP to solve this problem and established it's actually a matter of focusing that resulted in problems described (telescope was either too intrafocal or extrafocal), not collimation itself. This is a video on YouTube that OP said was exactly how the problems looked like. Granted, focusing can be technically called collimation too, and indeed that demonstration video calls it as such (albeit misspelled), since it's still about adjusting positions of primary and secondary mirror in dobsonian or newtonian telescopes (dobsonian is a type of newtonian), but the former is a lot simpler to solve by turning focusing knobs and achieve optimal illumination.
Now, let's answer the actual question.
Preparing our laser collimation setup
First thing to know is that any laser collimator will likely have the beam strong enough to cause damage to your eyes if pointed directly in them, or damage strong light sensitive equipment, like for example digital cameras, so be careful with it and take precautions. Carefully read instructions on how to handle and use it, before you do so. This is how a laser collimator might look like:
Next thing to do is make it functional by inserting batteries or plugging its power adapter and testing it actually works by turning it on with the switch, if it has it (probably does). Once you'll establish your laser collimator is turned on and functioning by observing (usually ruby red) light beam spot it makes on any neutral surface, turn it back off and attach any adapters on it you might need to help you attach it to your telescope's focuser. This is how your telescope's OTA (Optical Tube Assembly) might look like:
Now remove the barlov and eyepiece from your telescope's focuser if you're using a direct focuser adapter for your telescope model, tighten the laser collimator's compression ring by rotating its rubber ring and attach the collimator into the focuser. Rotate collimator's compression rings to tighten it in place. If you're not using an adapter, your laser collimator might attach directly to your eyepiece. Consult your collimator's user manual, if unsure.
Rotate your collimator's targeting faceplate towards your telescope's primary mirror (on the telescope's bottom) and turn on the laser.
Angular alignment of the secondary mirror
By looking into the telescope top down from the secondary (top) mirror into the telescope, we will adjust the angular alignment of the secondary mirror by referencing the laser dot projecting on the primary (bottom) mirror. The secondary mirror's support has a center ring, the collimating cap, with three bolts on the top of the secondary mirror holder. Use Allen wrench or Phillip's screwdriver to rotate them individually to bring the laser dot into the center of the doughnut ring of the primary mirror, like so:
Try to bring the dot more directly into the doughnut center than on the photograph above, though. I intentionally didn't select a photograph from when it was in its dead center, because of the light reflection covering the doughnut ring completely, rendering it nearly invisible.
Primary mirror collimation
Unlock the primary mirror plate locking screws, position yourself towards the panel side of the primary mirror tube so you can observe the laser's center spot on the targeting faceplate on the collimator and start adjusting collimation screws by turning them gently until the laser dot is in the center of the targeting faceplate:
Another way to check your collimation progress when adjusting collimation screws is by checking the projection laser dots on the secondary (top) mirror and making sure both laser dots are overlapping into one single spot, but that might make your adjustments of the primary mirror somewhat harder, so using the targeting faceplate of the laser collimator would be my suggestion and perhaps check alignment of the secondary mirrors laser dots projection for the last finishing touches to collimate your mirrors as precise as possible.
Now you're done collimating your dobsonian or newtonian telescope, so it's time to remove the laser collimator by first switching it off, then untightening its compression ring and taking it out of the focuser. Once you've removed the laser collimator, insert in the focuser barlov and the eyepiece, and tighten them back in place.
Additionally, and as requested, here is the Youtube video of the Newtonian Collimation using SCA Laser Collimator that are also the source of the last two example photographs and inspiration to write the collimation procedure, courtesy of HoTechUSA YouTube channel. Make sure to browse through other similar videos on telescope collimation in this same channel.
Collimation of a dobsonian without a laser collimator
Standard collimation technique for the exact dobsonian telescope make OP mentioned has can be read in this Instruction Manual for Sky-Watcher dobsonians (PDF):
Collimation is the process of aligning the mirrors of your telescope
so that they work in concert with each other to deliver properly
focused light to your eyepiece. By observing out-of-focus star
images, you can test whether your telescope's optics are aligned.
Place a star in the centre of the field of view and move the focuser
so that the image is slightly out of focus. If the seeing conditions
are good, you will see a central circle of light (the Airy disc)
surrounded by a number of diffraction rings. If the rings are
symmetrical about the Airy disc, the telescope's optics are correctly
collimated (Fig.g).
If you do not have a collimating tool, we suggest that you make a
"collimating cap" out of a plastic 35mm film canister (black with
gray lid). Drill or punch a small pinhole in the exact center of the
lid and cut off the bottom of the canister. This device will keep
your eye centered of the focuser tube. Insert the collimating cap
into the focuser in place of a regular eyepiece.
Collimation is a painless process and works like this:
Pull off the lens cap which covers the front of the telescope and
look down the optical tube. At the bottom you will see the primary
mirror held in place by three clips 120º apart, and at the top the
small oval secondary mirror held in a support and tilted 45º toward
the focuser outside the tube wall (Fig.h). The secondary mirror is
aligned by adjusting the central bolt behind it, (which moves the
mirror up and down the tube), and the three smaller screws
surrounding the bolt, (which adjust the angle of the mirror). The
primary mirror is adjusted by the three adjusting screws at the back
of your scope. The three locking screws beside them serve to hold the
mirror in place after collimation. (Fig.i)
Aligning the Secondary Mirror
Point the telescope at a lit wall and insert the collimating cap into
the focuser in place of a regular eyepiece. Look into the focuser
through your collimating cap. You may have to twist the focus knob a
few turns until the reflected image of the focuser is out of your
view. Note: keep your eye against the back of the focus tube if
collimating without a collimating cap. Ignore the reflected image of
the collimating cap or your eye for now, instead look for the three
clips holding the primary mirror in place. If you can't see them
(Fig.j), it means that you will have to adjust the three bolts on the
top of the secondary mirror holder, with possibly an Allen wrench or
Phillip's screwdriver. You will have to alternately loosen one and
then compensate for the slack by tightening the other two. Stop when
you see all three mirror clips (Fig.k). Make sure that all three
small alignment screws are tightened to secure the secondary mirror
in place.
Aligning the Primary Mirror
There are 3 hex bolts and 3 Phillip's head screws at the back of your
telescope, the hex bolts are the locking screws and the
Phillip's-head screws are the adjusting screws (Fig.l). Use an Allen
wrench to loosen the hex bolts by a few turns. Now run your hand
around the front of your telescope keeping your eye to the focuser,
you will see the reflected image of your hand. The idea here being
to see which way the primary mirror is defected, you do this by
stopping at the point where the reflected image of the secondary
mirror is closest to the primary mirrors' edge (Fig.m). When you get
to that point, stop and keep your hand there while looking at the
back end of your telescope, is there a adjusting screw there? If
there is you will want to loosen it (turn the screw to the left) to
bring the mirror away from that point. If there isn't a adjusting
screw there, then go across to the other side and tighten the
adjusting screw on the other side. This will gradually bring the
mirror into line until it looks like Fig.n. (It helps to have a
friend to help for primary mirror collimation. Have your partner
adjust the adjusting screws according to your directions while you
look in the focuser.) After dark go out and point your telescope at
Polaris, the North Star. With an eyepiece in the focuser, take the
image out of focus. You will see the same image only now, it will be
illuminated by starlight. If necessary, repeat the collimating
process only keep the star centered while tweaking the mirror.
There are such evidence in the case of Mars. Observations from Mars Global Surveyor show evidences of crustal magnetization. In particular, this magnetization has extensive, east-west trending linear features in Terra Cimmeria and Terra Sirenum. These are probably reminiscent of magnetic features associated with a reversing dipole.
There are no such evidence in the case of Venus: Venus has no intrinsic magnetic field today (contrary to the common belief, its inability to maintain a dynamo activity is either due to its chemical and physical conditions unable to form a solid core, either du to an early complete core solidification; it is not due to its slow rotation), and could not have maintained a remanent crustal magnetization, because its crust would have been to hot during its dynamo activity (above the Curie point).
Sources:
It will become a planetary nebula like e.g. the Cat's Eye nebula that was formed by the death of a star with about the same mass as the Sun ~ $1 M_odot $:
Composite image using optical images from the HST and X-ray data from the Chandra X-ray Observatory
The Sun, and any red dwarfs above about 0.25 solar masses, will expand into what's called a red giant, a late stage of stellar evolution. At this stage, the star starts to fuse different elements, and eventually throws off its layers as a planetary nebula, leaving behind a white dwarf made of carbon and oxygen.
A red dwarf that is too small to become a red giant will not turn into a planetary nebula: its fusion processes will eventually cease and it will probably produce a white dwarf made mostly of helium. But the main-sequence lifetime of these very small stars is longer than the age of the universe, so this has never actually happened yet. The helium white dwarfs that do exist were formed in binary star systems (and were formed during their complex dynamics).
Red dwarfs are small main sequence stars - the smallest and dimmest that are still able to fuse hydrogen in their core. Brown dwarfs are even smaller (in terms of mass), but cannot even fuse hydrogen - they are thought to be able to fuse deuterium and lithium. Stars smaller than a brown dwarf turn out to be gas giants like our Jupiter, Saturn, Uranus and Neptune.
One thing that seems to be clear is that HgMn stars have only an extremely weak net longitudinal magnetic field component, if any. Shorlin et al. (2002) did an early survey of HgMn, Am, and Ap stars, and detected no longitudinal magnetic fields in the former, with a median 1$sigma$ uncertainty of 39 Gauss. Makaganiuk et al. (2010) also found $B_z$ values of 0 in the stars they surveyed, with a higher precision - a 1$sigma$ uncertainty of 0.81-10 Gauss, varying between stars. Other studies also yielded precisions of less than a few Gauss for some stars (see mentions by Makaguniak (2011)).
Some reports have found longitudinal values in the 10s to 100s of Gauss, but as Kochukhov notes, subsequent inveistigations have failed to confirm these findings, which have had extremely high uncertainties. One example is Hubrig et al. (2012), the paper you cite, which claimed to have found weak longitudinal and quadratic fields in several stars, including HD 65949. Kochukhov et al. (2013) then found no longitudinal fields on the star, to within a few Gauss, and Bagnulo et al. (2013) attributed to 2012 findings to instrument error, leading to flawed data.
Non-longitudinal magnetic fields have not been observed in much detail (small-scale longitudinal fields have not yet been ruled out, either, by large-scale global ones appear to be nonexistent), and complicated ones could still exist. Kochukhov et al. (2013) do say that they have ruled out large so-called tangled magnetic fields, but small-scaled ones are still possible, according to Hubrig.
One thing worth noting is that the vast majority of these studies, including the one you referenced, which has been disputed, are focused on B-type HgMn stars, in part because fewer A-type HgMn stars have been discovered.
Stellar Mass black holes are (generally) black holes which form from collapsed stars. They get their name because the mass of the black hole is in the order of the mass of stars. I don't believe they would fit your definition of "Low Mass," as they are believed to be fairly standard in size.
Primordial black holes are theoretical black holes which were believed to have been created during the early moments of the universe. My understanding is that these would be a subset of quantum black holes, which also seem to be called micro black holes.
See this related question, in which the answer covers types of blackholes.
I'm not quite sure what the lower-end masses of observed black holes are, but in theory we could say that the lowest mass of a stellar black hole is just beyond the upper limit of mass for neutron stars, as above that limit they would be collapse into a stellar black hole. This is known as the TOV limit, and is approximated to be about 1.5-3 solar masses1, so we could say that the smallest stellar black holes could have a mass of about 1.5-3 times that of the Sun.
Note however, that this doesn't mean that the Sun is nearly massive enough to become a black hole. The mass of the resultant stellar black hole is only a small portion of the original mass of the star which created it.
The current model of cosmology starting with the Big Bang states that all spatial and temporal dimensions (Length, width, height, and time) as well as the four fundamental forces originated from a single point. With time starting with the big bang, there was no 'before', just like there was no up or down, no gravity or electromagnetism. There was no existing universe when the big bang occurred. It happened, and then the universe existed (causality).
So to say that it started in another universe would require a different hypothesis than the current cosmological model.
There are many challenges to formulating a hypothesis that could explain what you are asking. Some of these challenges are how to account for the laws of conservation of mass and energy. For example - if there was a 'sparsely' populated pre-existing universe, where did the mass and energy for our universe come from? Was it always there? If so it must have been in the form of some type of black hole. This much should be self evident - we can have black holes that exist in our universe with only the tiniest fraction of the total mass. If ALL of the mass were concentrated in one place, then it too would exist within it's own Schwarzschild radius. As a side note, it's a common exercise in college astronomy classes to calculate what the observable universe's Schwarzschild radius is. Surprisingly enough, our observable universe can be computed as existing within an event horizon, but these calculations require that there be a lot of assumptions of total mass and maximum extent of the observable universe (which usually limits the diameter to being smaller than what the Schwarzschild radius is prior to starting the experiment).
Another difficulty might be trying explain a black hole suddenly going into reverse and ejecting all matter/energy, spatial dimensions, fundamental forces, and time into an existing universe. How does that explanation then exclude all of the black holes that are thought to exist in the present epoch of our universe?
In short: We don't know for a fact that the universe we see today didn't already start in a universe which was in an existing state. However, to the best of my knowledge, there have been no attempts made to explain how a sparsely populated universe could suddenly grow a densely populated mini-universe inside of it. Any attempts that are out there may not have gained wide enough audience yet to include me.
Also, remember that for a hypothesis to become theory, it must be testable. There is no way to test events that occurred before the big bang. Therefore there is no possible way to test for the sparsely populated universe you asked about in your question.
The universe being open, closed, or flat only determines the type of geometry one must use to describe distances (and time). For open and closed geometries, Euclidean Geometry is not what one should use. I would also agree that our universe being open, closed, or flat has nothing to do with the number of dimensions it contains.
At present, there is no direct evidence that there are any additional dimensions over 3+1 dimensions (this just means three spatial dimensions and one time dimension). However, many GUT theories do include additional spatial dimensions in an attempt to unify all of the forces.
Also at present, we have very good evidence that the universe is 'flat'. What this means is that the angles of a triangle have to add up to $180^{circ}$ and distances are measured in the standard Euclidean way. When we talk about the universe being flat, this is a purely global statement. Locally, however, it is completely possible to live in curved space. We actually do live in curved space. The mass of the Earth is curving space and time in a way that General Relativity predicts, and therefore clocks run very slightly differently depending on where you are on the Earth's surface, and distances are very closely approximated by Euclidean distances, though they're not.
How do we actually determine that the universe is globally flat, you may ask? We use what's known as a standard ruler. Much like a standard candle, if we think we understand the physics, any deviation from what we would predict gives us new information about the universe (in the case of supernovae, it's that they can be used to measure distances, and therefore map out the expansion of the universe). We use the angular size of fluctuations in the Cosmic Microwave Background Radiation (we think we understand the physics behind the fluctuations fairly well) to test how much, if at all, the universe deviates from flatness. The latest results from Planck show very good agreement with the standard picture provided to us by the standard LCDM cosmological model.
Below is the power spectrum of the temperature fluctuations of the CMB. The location of the first peak is what cosmologists use to measure flatness.
In quantum field theories, interactions are exerted by the exchange of a force carrier particle. For the electromagnetic force, this is the photon, for the strong force, the gluon and for the weak force, the W and Z bosons. All these force carrying particles have been observed.
Now it is imagined, that if we are able to find a quantized version of gravity, it would also be described by a quantum gauge field theory. Then the force would be exchanged by a messenger particle as well. This messenger particle is the graviton. It has spin 2. We haven't observed this particle yet.
Mu Sagittarii is a star system, not a single star. If that can be included, then Eta Carinae should be included, and it has an absolute magnitude of -12.0. It's a star system about 7,500 light-years from Earth.
It looks like the brightest (absolute magnitude) single star visible to the unaided eye is WR 24 (in Carina Nebula). Its absolute magnitude is −11.1 and apparent magnitude is 6.48, so just barely visible.
source: Wikipedia - List of most luminous known stars
edit: Rho Cassiopeiae's absolute magnitude is -9.5.
I guess theoretically if we could go faster than light, which we clearly cannot, at some point we'd be able to see the big bang itself.
If we travel instantaneously across the universe (as measured by cosmological time), then no, theoretically that's not the case. Our theoretical assumptions involve large-scale homogeneity and isotropy, meaning that the view different observers is basically the same regardless of where they are, at least at the same cosmological epoch. This is called the cosmological principle.
Mind, because of the way relativity works, an FTL drive might also be capable of taking you back in time, so perhaps you could theoretically see the Big Bang after all. But that's obviously more to do with time travel than going to distant places.
Seems like the moment something happened, light was dispatched and unless particles traveled faster than the speed of light to obstruct that light, if I were to appear in front of that light, for a single tiny moment, I'd see that little white dot that would've appeared the moment the big bang began (and then see everything that happened afterward). Why not? Light point A -> same light at point B [observer]. Where's the complication?
You seem to have an implicit assumption about where the Big Bang occurred. It actually occurred everywhere. Including here. See this question.
Imagine looking out to the most distant galaxy that you can barely see. Because of the finite speed of light, you are looking at it not as it is, but as it was in the distant past. You are just now catching light from that distant place.
If you were instantly transported to that place, and look back to where the Milky Way should be, you won't see it, but rather as this area of space was in the distant past. You'll be just catching light from somewhere the Milky Way area.
In other words, you will see light from the distant past no matter where you go. Because the Big Bang happened everywhere, light from it (well, actually from recombination epoch later, because the universe wasn't transparent before then) is present everywhere. And hence it'll look about the same no matter where you go, again assuming isotropy and homogeneity.
Given that the stars' distances to Earth are measured in light-years (for example, Sirius is 8.6 light-years away from Earth), what we are seeing as Sirius now is actually its state 8.6 years ago, right?
So it is possible that a star (maybe not Sirius, I don't know, it's just an example) somehow explodes and creates a supernova, and if this is the case, we will see this event 8.6 years later (I assume everything is right up to this point).
So my question is, is it possible for me while looking at the sky on a lucky day, suddenly see the explosion of a star that happened x years ago and be the first eye witness of this event? In other words, is there a technology on Earth (emphasis on "on Earth" here, the satellites or space shuttles do not count since they might be slightly closer to the star than the Earth is) that can see this before me?
My logic is that even the greatest telescope "sees" whatever light it receives. So since a telescope cannot increase the speed of light it receives, it shouldn't be more fast than me. And since light is the fastest way of transferring information, I assume that I am as possible as NASA to see such an event. Is there any way this assumption is wrong?
I'm currently working on an independent project that involves discerning starburst galaxies that are themselves within active galaxies.
I would assume radio observations would be best to discern star formation rates, and X-ray to understand the AGN in greater detail. However, assuming we have only optical data could I use the relative strength of the OII flux to the OIII flux to better understand the star formation rate of an active galaxy? Spectroscopic surveys of distant galaxies, particularly for redshifts between $z$ ≈ $0.4$ to $1$, routinely use [O II] $λ3727$, a prominent nebular emission line in H II regions, to estimate SFRs. If (high-ionisation) AGNs experience substantial levels of ongoing star formation, the integrated contribution from H II regions will boost the strength of the [O II] line (compared to, say, [O III] $λ5007$, which can be largely ascribed to the AGN itself).
metallicity is a complicated issue, and giving just one number (usually Z, but also 12+log(O/H), ...) is very rough. But, here are the standard values for the Magellanic clouds:
LMC: Z~1/2
SMC: Z~1/5
with Z=1 being the solar value. Practically, the values will vary across any given galaxy (the Milky Way also has a metallicity gradient).
Reference:
Madden et al. 2014, PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF THE PACIFIC, 125:600–635, 2013 June
http://adsabs.harvard.edu/abs/2013PASP..125..600M
The article is also available on astroPH
Yes, in an expanding universe there is an increase in potential energy (with same caveats).
The (Friedmann) equations of a homogeneous and isotropic universe with no spatial curvature or cosmological constant can, in fact, be derived very easily from nonrelativistic Newtonian gravity. (This derivation is shown, e.g., in Mukhanov's Physical Foundations of Cosmology.) So it is actually valid to think of such a cosmos in Newtonian terms, using randomly but approximately homogeneously distributed point masses. At early times, the point masses are flying apart at high speed but the average distance between them is small. At late times, they will have slowed down, but the average distance between them will have increased. All that kinetic energy is converted into gravitational potential energy. This also remains true if we take into account Newtonian perturbation theory (the growth of overdense and underdense regions from initial perturbations).
As for the caveats: First, as I mentioned above, when spatial curvature is present, the Newtonian solution is no longer valid. Second, there is a century of literature with a variety of attempts to define a meaningful stress-energy tensor for the gravitational field in general relativity, none completely satisfying. Last but not least, a cosmological constant/dark energy term adds its own interesting twist to the story, as its energy density remains constant in an expanding universe, causing the expansion to accelerate: in this case, both the kinetic and the potential energy increase, thanks to the role played by dark energy's negative pressure.
The only way you can use Hubble to view the Earth "in the past" is to swivel it and point it at the Earth now. Assuming that this didn't break the telescope (it would) you would collect images of the Earth's surface that were approximately $500times10^{3}/3times10^{8} = 0.0017$ seconds old, since that is how long it takes light to travel from the Earth's surface directly below HST to its $sim 500$ km orbital height above the Earth's surface.
The problem with what you suggest, is that although we might be able to pinpoint where the Earth was in the past with respect to its position now and the Galactic centre (actually that would be very hard in practice), the light that came from the Earth then has long since travelled beyond where the Earth is now.
For instance, let's say the Earth/Sun travel around the Galaxy at approximately 230 km every second and say we want to look at the spot where the Earth was 1000 years ago. Well, it turns out then that the Earth was at some location in space that is currently about $7times 10^{12}$ km away (7 trillion). But the light that came from the Earth then, has already been travelling outwards at the speed of light for 1000 years, covering a distance of 1000 light-years, which is about $10^{16}$ km. So that light passed by our current location in space more than 999 years ago.
