Are the pictures with millions of stars & nebulae in them real?

The photos in which millions of stars can be seen alongside several nebulae- are these real or edited? If the former, are they taken from space? Can you see them from the naked eye?

While there are certainly a number of edited space pictures floating around the internet, there are also a lot of real pictures like what you describe. The most famous of these tend to be of the Orion Nebula - it’s a very beautiful nebula (along with being scientifically fascinating), so lots of people - both professional astronomers and amateur astronomers - have taken pictures of it. (The Trifid Nebula is another common target.)

Why are there so many stars in these pictures? Almost all of the gas (and most of the stars) in our galaxy is contained up in a very thin disk - proportionally, the Milky Way is thinner than a razor blade. This means that all these nebulae - which are clouds of glowing gas - are also found within this very thin disk. If we look towards them, we are looking through the disk towards the greatest concentration of stars in the sky. The thousands and thousands of stars captured in these images are just the handful of the stars in our galaxy that happen to be in the same direction as the nebula. The fainter the nebula you’re trying to observe, the more stars you’ll capture.

These nebulae can be imaged either from the ground or from space - it depends on what we need the pictures for. The pretty Hubble images you see are usually not the main goal of pointing Hubble at that patch of sky - scientists are usually concerned with how much light there is of a certain colour in a certain region, and whether or not there is more of a certain colour than a second color - these differences in colour can help us understand the structure of the nebula, and how warm or cool it is, along with a number of other properties. This information can be used to make a colour image of the nebula, but it often isn’t done right away, or at all.

If, however, you’re simply wanting to make a really good-looking picture of a photogenic patch of the sky, you would do that from the ground. There are so many things that only space telescopes can do, that we can’t spend much (or any) time just to get good pictures. But on the ground, your time is less constrained, and a lot of amateur astronomers have their own telescopes and cameras attached to them, so they can just go out and take pictures whenever the sky is dark and clear. In this case, these detailed pictures are taken over a long period of time, to make sure that there’s enough time for the light from all those stars to reach the camera.

Most nebulae are too faint to be seen with the naked eye - but the Orion nebula is a notable exception. If the constellation Orion is up, look for the middle “star” in Orion’s sword - it’s actually the Orion nebula. In a very dark sky, it might even look a bit pink.

Have your own question? Something here unclear? Feel free to ask! And remember, there’s also facebook, twitter, and the sidebar for your questions!

What happens when light hits an atom in space?

This dramatic image offers a peek inside a cavern of roiling dust and gas where thousands of stars are forming. The image, taken by the Advanced Camera for Surveys (ACS) aboard NASA/ESA Hubble Space Telescope, represents the sharpest view ever taken of this region, called the Orion Nebula. Image Credit: NASA, ESA, M. Robberto ( Space Telescope Science Institute/ESA) and the Hubble Space Telescope Orion Treasury Project Team

This dramatic image offers a peek inside a cavern of roiling dust and gas where thousands of stars are forming. The image, taken by the Advanced Camera for Surveys (ACS) aboard NASA/ESA Hubble Space Telescope, represents the sharpest view ever taken of this region, called the Orion Nebula. Image Credit: NASA, ESA, M. Robberto ( Space Telescope Science Institute/ESA) and the Hubble Space Telescope Orion Treasury Project Team

Light is an interesting beast.  We treat it as a particle (the photon) that travels with no mass and at the fastest possible speed through the universe.  But light also behaves as a wave; it has a frequency, or a color, associated with the amount of energy it carries.  The more energy a photon carries, the bluer its color.  (This trend continues far beyond the visible range of light; radio waves are the reddest color of light, and gamma rays are the furthest to the blue.)  When light interacts with an atom, a number of things can happen, depending on the complexity of the atom and the energy of the photon.

Let’s simplify things by dealing with hydrogen.  It’s the simplest possible atom, with one proton and one electron, and it’s what the majority of the universe is filled with.  The electron is bound to a region of space around the proton by a series of electromagnetic barriers, but if you had enough energy to donate to the electron, it could bounce its way over the barriers and wander around space freely.  

This is where light comes in - photons are very effective carriers of energy.  Depending on the source of the photon (normally a nearby star), they can be more or less energetic.  The redder the nearby star, the lower the average energy of the photon you get.  We’ll take one of these photons, and smash it into our atom.

If the energy of the photon is less than the amount you’d need for the electron to hop out of its electromagnetic moat, the electron will remain stuck to its proton.  However, our electromagnetic barrier has a series of little ledges in it where an electron can hop up and stay for a little while.  If the energy of the photon happens to match up with the amount of energy the electron needs to jump up to one of these ledges, the photon will get completely absorbed.  The electron won’t stay there forever, and when the electron drops back down to the bottom of the moat, it will emit light of the color that corresponds to the amount of energy it took to get to the ledge.

If, however, the photon happens to be energetic enough for the electron to break free from its proton, you have successfully ionized an atom!  The electron will wander around aimlessly for some time, until it encounters a lone proton with no electron.  The electron will fall back into the potential well, which undoes the ionization of the atom.  The electron has to lose energy to do this, so it spits out a photon with a color corresponding to the amount of energy lost.  If you have enough hydrogen floating around in the same place, you wind up with a cloud of glowing gas - but only glowing at very specific colours!  This complex sea of escaping and recaptured electrons is what lights up an emission nebula.

Have your own question? Feel free to ask! Or submit your questions via the sidebarFacebook, or twitter.

Sign up for the mailing list for updates & news straight to your inbox!