Over the years I’ve accumulated a lot of astronomy and astrophotography wisdom which is easy to take for granted. Advances in imaging techniques continue to draw more people to the hobby – and often these folks have a good understanding of photography from their DSLR cameras. However, not everyone has this background – nor a PhD in astrophysics. My goal here is to share the wisdom I’ve learned in a way that’s not too complicated for the reader without either of those backgrounds.
The new entrant to amateur astronomy has presumably used their unaided eye to view the sky. If bound to a city or suburbia, it might seem there are so few stars out there that one could count them all in a night. If in a rural area with no city light pollution nearby, the sky bursts with so many stars that even finding the constellations can be a real challenge! Driving to a “dark sky” location only to realize one has no idea how to find anything can be a real challenge. However, technologies today can great assist even the most novice amateur and turn a single night of scouring the sky to find one object into a night filled with too many things to see.
But, what can you see? Your naked eye will let you spot the moon, planets, stars, and if one is lucky enough to be in an extremely dark place, wonderous objects such as The Andromeda Galaxy and even some globular clusters can suddenly pop into sight. What about everything else?
Stuff in space varies in size, brightness, and distance. For example, if someone shines a flashlight in your face from a few inches away, it appears very big and very bright. But take that same flashlight across the room, and suddenly it’s not very big, although perhaps still bright. Take it a few miles away and suddenly it is so small and so dim that you might not even be able to see it anymore.
Astronomers use the term apparent size to refer to how large an object appears to be when you look at it from Earth. The term apparent magnitude refers to how bright something is when viewed from Earth. Often people will drop the word “apparent”, and simple talk about size and magnitude.
The sky is divided up into 360 degrees, like a circle. Each degree can be further divided into 60 equal sized sections called minutes, and each minute can be further divided into equal sections called seconds. A good way to get a grasp for these concepts without breaking out the geometry book is to use the full moon. The size of the full moon when viewed from earth is about 1/2 degree, or 30 arc minutes. To build a simple ruler, hold your hand away from your face and look up at the moon. How many fingers do you need to cover the moon? Now you can roughly measure angular distances between things in the sky in terms of moon widths.
Brightness of objects is measured with a number called magnitiude. The smaller the number, the brighter the object. The bigger the number, the dimmer. For example, the sun is magnitude -27. The full moon is magnitude -13. Jupiter gets to about magnitude -3. The dimmest stars visible in a city are around magnitude 3. Under very dark skies, the eye can pluck out stars to magnitude 6. Binoculars can get you to around magnitude 10 and a reasonable telescope will get to magnitude 14.
So, depending on how clear the sky is, how dark the sky is, and what type of instrument is being used (if any), the types of things you can see will vary widely. Even with binoculars, the beginner ought to stick to large, bright things — magnitude 5 or brighter, and things with a angular size over 10 arc minutes (1/3 the size of the moon).
A word on binoculars: Binoculars are a great way to get started with the skies beyond naked-eye observations. They’re readily available, affordable, extremely easy to use, comfortable to the eyes, and greatly expand the number of things you can observe. Even without a mount, they are still great to lay back on the ground and just scan the skies. Plus, you can take them to your favorite football or baseball game without looking crazy!