# Tag Info

28

It appears to be static because it's huge beyond your imagination. The distance to the nebula is 7,000 light years. Its apparent size is 7 arc minutes. Therefore its linear size is about 14 light years. Think about that. The whole nebula is so big, it takes light 14 years to cross it. Any motion therein must necessarily be much, much slower. No wonder you'...

19

To add to Florin Andrei's answer, with an image height of 7,000 pixels for 14 light years, that's 17.5 light hours per pixel. That's 20 billion kilometres per pixel. To make a change in a single pixel over that time, something of that size must have either changed composition dramatically (to give a different colour or opacity) or it must have moved by a ...

14

Cosmic GDP has already crashed, as Peak Star was ~11 billion years ago. According to Sobral et al's prediction, the future star production by mass will give only 5% of the stars in the universe today, "even if we wait forever." More theoretical predictions, such as this one, suggest that nebulae will run out of hydrogen on the order of $10^{13}$ years, ...

12

I think my deleted answer to your previous question covers this well, so I'll add it here. These two spots are known as the east and west bays of the Crab Nebula. They appear to be the result of a torus partially encircling a section of the nebula. The pulsar's magnetic field interacts with the gas and dust in the torus, which blocks synchrotron radiation ...

10

If you go to this site, http://heritage.stsci.edu/2015/01/supplemental.html , there is a set of comparison photos. The movement that is detectable is very slight but it is there.

9

Barnard 68 has a surface area of around 10 square arcminutes on the sky and is at an estimated distance of around 160 pc. The volume of space encompassed by a sightline to Barnard 68 is therefore about 1 pc$^{3}$. The the density of stars in the solar neighbourhood (hydrogen burning stars with mass above about 0.1$M_{\odot}$) is about 0.1 pc$^{-3}$. So it ...

9

The size of cosmic dust grains is in general given not by some size, but by a size distribution. The only direct measurements of such a distribution are made on dust collected on plates of satellites, which is of course a very local measurement. When we think that distributions look similar — though not exactly alike — in other locations of the Universe, so ...

8

Stars are responsible. HII regions$^\dagger$ can refer to several things, but usually I guess one thinks of the volumes around star-forming regions. The more massive a star is, the faster it burns its fuel, and at a higher temperature, meaning that the peak of their spectra are more toward the high frequencies. The most massive stars of a stellar population ...

8

In the best sky conditions, the naked eye (with effort) can see objects with an apparent magnitude of 8.0. This reveals about 43,197 objects in the sky. There are 9 galaxies visible to the naked eye that you might see when observing the sky, and there are about 13 nebulae that you might see. Sources: The Bortle Dark-Sky Scale - John E. Bortle How many ...

8

Yes, indeed! Many nebulae are visible from Earth in a small and cheap telescope, and even to the naked eye (if you are standing in a sufficiently dark place). In fact, yesterday I was watching the Orion Nebula with my 4.5" telescope (which is worth $200 or so) from my apartment in the middle of Copenhagen. The term "nebula" is a bit of a… well, nebulous ... 7 With an 8" scope, a filter will very likely give you better results than observing without a filter. Although a filter does block light, the crucial aspect is that a filter increases contrast (by blocking light pollution and extraneous wavelengths of light more than the nebula), thereby allowing you to spot low contrast diffuse nebulae (like IC59 and IC1318) ... 6 The Boomerang Nebula (or Bow Tie Nebula) is a cloud of gas being expelled from a dying low-mass star, at$164~\mathrm{km}~\mathrm{s}^{-1}$. In general, when a gas expands, it cools (see extended explanation below). If the gas were optically thin to the CMB — that is, if it were sufficiently dilute that CMB photons could easily penetrate — it ... 6 "Nebula" is quite an imprecise word; over the years, it's been applied to everything from interstellar dust clouds to supernova remnants to the birthplaces of stars to even galaxies. Wikipedia separates true nebulae into four categories: H II regions, planetary nebulae, supernova remnants, and dark nebulae. In this case, it might be better to make the ... 6 The very first stars to form indeed consisted essentially only of hydrogen and helium. When stars die, they leave behind them more massive atoms, as you say. These heavier elements are too incorporated in newer stars when they form. This results in stars which start out with a lower portion of hydrogen and helium, thus making them somewhat less effective; ... 6 The colorful patterns of gas are caused by excitation of gas atoms, e.g. oxygen, from radiation of a nearby star. You would see the same colors as from a distance, as the light is emitted in almost random directions. But you wouldn't see the same region of nebula shining at the same time as seen from Earth, when excitation is caused by a flash of radiation ... 6 First query: YES there are many bok clusters without foreground stars. For density, That's an unclear field of study, confused with dark matter enigma, and the estimates of frequency of "Boks" perhaps only have about 1-2 degrees of magnitude precision. We can't say that there is less than 1 bok for every 10 stars, we can't say there is more than 1 for ... 6 This appears to be one of Sergii Tsololo's more convincing efforts in the synthetic "space" image genre. It is listed on various stock photo sites as "Blue and purple space galaxy," or with added 4-way spikes, "Blue space starfield with flares." A real astrophoto would identify the subject and not be tagged "abstract" or "fantasy." To check it another way, ... 6 There is an article here that describes the visible effects quite well. In essence, within a week or so, it would be comparable in brightness to the moon and therefore visible during the day. Betelgeuse would then start a phase of final, rapid dimming and again reach its current brightness level after possibly three years. After six years, it would be ... 5 The answer is that in a pre-supernova star, most of its mass is still in the form of hydrogen and helium. It is only the central core where the primordial H and He has fused to heavier elements. This picture of onion layers is typically what you see in elementary text books. It is completely misleading in a quantitative sense. It schematically represents ... 4 Dark Skies are your friend. When Messier was searching for comets, it was before electric lighting and the nights were dark in a way that is rarely seen today. Take a look at the Dark sky map, and try to get somewhere in the blue or black region. Then allow your eyes to become dark adjusted, and to look with the edge or your vision, or learn to do ... 4 No, those are two different nebulae. There are stars in our galaxy much older than 5.6 billion years. The problem is that "nebula" is a very generic term, so it can be a whole galaxy or even the remains of a single star. It's not even clear what is meant by the nebula from which our Sun formed, it could be the giant molecular cloud if our Sun formed in a ... 4 This is an excellent question. Think about the way in which emission happens.$\text{H}\alpha$emission happens when an electron makes a transition from the third energy level to the second, emitting a photon in the process with the energy equivalent to the difference of the energies of the two states, roughly$1.9\text{ eV}$. There's a lot of hydrogen in ... 4 Not noticeably darker. Assuming such a globule has a mass of 50 solar masses and a diameter of 1 light year, that would make it's average density about$2.2\times 10^{-16}\,kg\,m^{-3}$which is fairly close to not being there at all in human terms. An imaginary tube of this stuff 1 AU tall and of area 1 meter squared would contain about$3\times 10^{-5}\,...

4

Very large (for amateur) scopes in very dark places, with healthy eyes on a good night have credibly reported seeing color in nebula. The Orion is about as good as it gets, lots of photons, my eyes are not particularly good, but have been out with others who claim noticing color in the Trapezium in a thirty-ish inch reflector

4

Those targets are good choices for beginners at the right times of year. However, in June M42 is a daytime object, and M31 rises in the wee hours, leaving only M13 and Albireo in the evening. Other good summer targets include: M8, the Lagoon Nebula M11, the Wild Duck Cluster M57, the Ring Nebula Precise polar alignment is only required if you plan to take ...

4

Yes, nebulae can often have very distinct colours. What produces those colours can depend on what elements are in the nebula material and what the temperature and density are. Generally speaking, green colours in a nebula are due to forbidden transitions in ionised Oxygen, though can feature the hydrogen $\beta$ Balmer line. Red colours can be due to ...

3

You might be interested in these two answers from the Physics.SE site: How dense are nebulae? Excerpt: If you were within a nebula, it is hard to say what it would look like. But nebulae are so large that the optical depth of the cloud would actually probably be quite high, and I would guess that it would look like you were surrounded by glowing green ...

3

This is a very complex answer. It has to do a lot with gravity and electromagnetism. Nebulae are made of particles that act according to those forces and give you the illusion of viscosity. Those particles are actually moving. Take a look at this simulation it might give you an idea: Simulation

3

The size of the nebula doesn't matter at all, what matters to the size of a star is the mass and age of that star. Even the mass of the nebula doesn't really matter, because giant molecular clouds fragment dramatically as they make many many stars. It's a very complicated and detailed process that controls how they fragment, so usually one merely assumes a ...

Only top voted, non community-wiki answers of a minimum length are eligible