When you sell telescopes in a big city people do tend to ask what they can do to use their telescope despite the bright lights of the city washing things out. We have many hints, of course, but sometimes folks just don’t want to make much effort to view at all. In fact, instead of taking their telescope onto a deck, or a roof, or to a dark area some of them ask: Can’t I just point it out my window and see stuff?
Now, I’ll admit that sometimes lazy astronomy can be very tempting. Telescopes can be heavy or bulky and carrying them up small ladders some decks and roofs use can be downright dangerous. It can be very tempting to imagine oneself resting in a warm, comfy chair gazing at a telescope aimed through a window into the great skies.
Hollywood, once again doesn’t help things very much. The ‘telescope-pointed-
out-the-kids-window’ is used so often it might almost be a trope or cliche at this point. The fun part is that most of the time the kid in the movie doesn’t even look at the stars but manages to spot a crashing UFO. Also famous are fancy astronomical telescopes place in bay windows in mansions. It conveys the impression that the telescope is going to used by viewing through the windows.
But enough of Hollywood causing misperceptions for now. The fact is that looking through your telescope through a window, open or closed, is just not a good idea. Let us explain why:
First of all, understand what went into making your telescope. That mirror or that lens on it? It was polished to an incredible level! That mirror is polish to a 1/4 wavelength of light. That’s right, its accurate to one-fourth of a wavelength of light. In case you weren’t aware, wavelengths of light are very small, being measured in nano-meters. So you’ve got yourself a very well made indstrument at work here.
Now that window glass? Not so much. It was made for size and economy. For starters it is going to lose 8-9% of the light just from when it strikes the glass surface, then the rest that goes through? Its going to get badly distorted.
Go over to a nearby window and take a look at it – AT it, not through it. It might look clean, it might seem flat, but look closer and you’ll see that it has distortions, waves, bubbles, and more. These are all things that will mess up your view if you aim your telescope through window glass.
Aiming your telescope through window glass is like getting a fancy sports car, and then yanking out the powerful V-8 and putting a two-stroke motor from a lawnmower.
Now you might think to yourself “well, OK, the window is lousy, but I’ll just open it, and that screen window as well and everything will be fine!”. Sadly this doesn’t work very well either. The reason? Temperature.
You see, with very few exceptions most days the temperature inside your home is going to be dramatically higher or lower than the temperature outside. Even on the best of days it is going to be slightly different. That is going to cause problems, and not just because you’d be wasting energy.
If you ever seen waves of heat coming off terrain on a hot day or seen the distortion of air caused by a hot radiator then you know what heat can do to the air. The difference between the outside air, inside air, and even the air inside your telescope’s tube can seriously mess up the image. Even different humidity levels can cause distortion. In fact, temperature differences are such an issue that astronomers who use their telescopes outside often use fans to cool the tubes down faster. Many Dobsonian telescopes now have wood or plastic knobs attached to the bodies so that the astronomer’s hands don’t heat up the metal (and thus the air in the tube) when aiming the telescope.
So while hauling the telescope outside can seem a bit daunting, it is without a doubt the best way to get the best out of your telescope. Viewing from within city limits may not make for idea viewing conditions, but viewing within apartment limits is most certainly worse. Get the most out of your telescope and take it outside to view!