Banner photo: Credit: Richard Yandrick (Cosmicimage.com)
Yes! You can see color in some astronomical objects! The planets are paramount in this area. Mars looks orange, with some darker areas (although they’re tough to see without a good filter, like the Baader Moon & SkyGlow). To my eyes, Jupiter is a bit yellow-y, with dark brownish belts. The Great Red Spot doesn’t really look red to me. Saturn is a very distinct yellow. Uranus and Neptune are tiny, tiny dots, bigger than stars, though, and are a distinct blue/bluish-green.
You can also see color in certain stars. Some of the brightest stars are red giants – Arcturus, Antares, Betelgeuse – and they all appear different shades of orange. There are also stars called carbon stars that appear different shades of red. Some astronomers enjoy hunting down carbon stars to see these various shades.
There are some famous double stars, like Albireo, where the two stars appear as different colors. I’m not gonna tell you which ones, because part of the fun is determining what colors you’re seeing. Okay, okay, that’s actually a picture of Albireo at the top of this post. There’s another pair in the constellation Canis Major that’s been dubbed the Winter Albireo for the same reason – the contrasting colors of the two stars. There are plenty of these double stars that exhibit color for you to explore.
Rods and Cones
You can see color in space – or at any other time, for that matter – because you’ve got two types of light sensors at the back of your eye (the retina): rods and cones. The cones detect color, but they need a certain amount of light to hit them before they activate, before they turn on.
With planets, they are bright enough, there is enough light coming from them, to be able to activate your cones, so you can see color when you observe them. The stars I’ve described are all dimmer; however, they’re all point sources of light: all the light is concentrated down into a tiny space. That’s enough to activate just a few cones on your retina and let you see color.
On the other hand, the rods detect dim light, low light, like when you’re outside at night, away from the streetlights. Notice how under those conditions, you can’t tell the grass is green. Rods only show differing shades of gray depending on how much light there is. Rods are able to detect lower and lower levels of light as time goes on, as long as they’re not exposed to a bright white light source. This is called dark adaptation. (Be sure to eat all your carrots! They have lots of Vitamin A, key for good night vision.)
Unfortunately, other than what I’ve described above, no other stuff up there is gonna show you any color visually. At all. Even though the moon is very bright, sometimes painfully bright through a telescope (a moon filter is great for these situations), the moon is still very gray. But that’s just because the surface of the moon really is very gray. Globular clusters and galaxies are also very grayish. The stars in open clusters are usually just white pinpoints. Nebula are definitely very gray.
Most astronomical objects don’t have enough surface brightness to activate the cones, so all you end up seeing is gray. If you get a large enough telescope that collects enough light, you may start to see colors in, say, a nebula. With enough light collection = enough aperture, the Orion Nebula (M42) will start to look green, because the cones that are sensitive to green light get activated first, with the least amount of light. But you need a huge honking telescope to see that – like 16 or 20 inches! That’s not a size telescope that I would recommend to a beginner just starting out; but it certainly is an end goal to eventually shoot for. Come on, Mega Millions!
Cameras vs. Eyes
As a result, oftentimes, beginners are completely underwhelmed by what they see when they look through a telescope versus what they’ve been seeing online. Pictures taken by Hubble and other space observatories, even pics taken by very talented amateurs who post them on Facebook or in other astronomical forums, have led to unrealistic expectations of what beginners will see when they finally buy that first scope and get to the eyepiece for the first time.
Sad to say, but for the most part, visually, with your eyeballs, diffuse nebulae and especially galaxies simply do not look like the glorious pictures you’ve seen of them, neither in their color, nor in their extent. As a preliminary matter, light pollution washes out these objects. Light-polluted skies make it more difficult to even pick them out from the gray (as opposed to black) background sky. Even if you do get your scope out to dark skies, you won’t see too much in terms of structure, and even less in terms of color.
The small and medium-sized scopes that most of us use, from three and four-inch refractors and Maks, all the way up to eight to ten-inch dobs and SCTs, simply don’t collect enough light to either 1) show your eyes the detail that a camera can capture; or 2) show your eyes the color that a camera can capture.
Cameras take longer exposures than the eye does. In the “olden days”, a dozen or more years ago, you’d take a picture of a DSO on film, in one long exposure, a half hour, an hour, two hours long. Nowadays, taking pictures of astronomical objects generally involves taking a series of much shorter exposures, each of which is anywhere between 30 seconds long and 5 minutes or so, and then combining each of these exposures with many others in a process called stacking to become many minutes or even many hours of light collection.
The combined stack can end up being practically any length – even if you take a total of ten minutes or even ten hours of exposure on one night, you can go back to the object night after night and keep collecting even more light. More light means more detail, more color. So, for example, let’s take a look at the Whirlpool Galaxy, M51. Here it is in all its glory:
Gorgeous, right? In both color and detail, this galaxy has got the goods. So, that’s obviously a long-exposure photo. In other words, a video of the galaxy taken for a long time, probably a couple of hours of exposure depending on what aperture was used, and then stacked. But this photo below shows about what it looks like visually through an 8 to 10-inch scope under dark skies:
Take a good long look at this photo. It’s oriented the same way as the first one, with the satellite galaxy off to the left. It’s a frame of a video posted on Youtube by someone calling themselves “Space Central”. The bright cores of each of the two galaxies are easy to see, of course. But other than that, there’s absolutely no color, and there’s precious little detail. You’re barely able to make out the spiral arms, and you can’t see the arm that connects the two galaxies. In real life (as opposed to using a camera), it is visually difficult to even make out this level of detail in the spiral of the main galaxy. It generally just appears as a gray haze around the core.
You just don’t see the same level of detail, of color, as in a photo, visually, because your eyes don’t work like a camera. Your eyes only stack light for about a tenth or a quarter of a second, and then stop. So, your eyes don’t continue to collect more light, more color, the longer you observe.
However, your eyes do collect more detail; in a way, at least. When you go from not observing – you know, looking around, looking at the scope, looking at the ground, getting ready to observe – to observing through the eyepiece, your eyes do need some time to adjust to that change. As you put your eye to the eyepiece, it takes a little while, up to half a minute or so, for your eyes to fully adjust to what they’re now seeing.
Plus, the effects of seeing come into play as well – the inherent turbulence that’s always present in the atmosphere. That turbulence robs you of detail – “twinkle, twinkle, little star” is not your friend. But every few minutes, for a few seconds, the atmosphere will settle down, get real quiet and still, and then the detail will suddenly emerge. This is why we don’t just look at objects for 30 seconds or a minute; we observe them for 5 minutes or more.
My advice to beginners: don’t let the fact that there isn’t much color – or detail – up there in most DSOs dissuade you from buying a scope. The stuff you’ll be able to see will still be pretty amazing, even if it’s just in differing shades of black and white.