AOP Home | Calendar | History | Sitemap

Beginner's Guide

3.   Where are the stars?

Now that you know what comets and asteroids are and what to expect to see when looking for them in the sky, let's go outside and look up. (Kids, make sure you have a parent or adult supervisor with you. And make sure to wait till about an hour after sunset!)

You're outside, it's dark, you look up... and see... nothing?! Where are the stars? First, make sure it's not cloudy. You're not going to see anything but clouds if it's overcast! And make sure you're not standing under a bunch of trees.

Okay, it's dark, (weatherman says it's) clear, but still no stars! Don't despair... just give your eyes several minutes to adjust to the dark (try not to look at the streetlights, cars, etc!). In a few minutes you'll notice it's not so dark after all. Street lights, cars, and lights on buildings and billboards provide enough illumination to see the ground. And unfortunately, they light up more of the sky than we'd like (it's called light pollution). Now look up. You should be able to see a few stars. If you watched the sun set, then you know which way is roughly west (the sun sets in the west) and by the process of elimination, you know which way is roughly north, east and south. If you didn't see the sun set, then you'll need a compass to help you figure out which way is roughly north. Let's double check. If you are looking roughly north, you should be able to see the Big Dipper somewhere up there. In the summer evenings, it will be high in the NW, but during the winter it will be low in the NE. We want to find the Big Dipper because it helps us to find the North Star (Polaris).

Big Dipper around the seasons
Fig 1: The position of the Big Dipper in the evening during the Winter, Spring, Summer, and Fall for mid-northern latitudes.

Once you find the Big Dipper, look for the two brightest stars in the bucket and they'll point to the North Star. Once you find the North Star (aka Polaris or α UMi), you'll notice that it's not that bright. Polaris is not the brightest star in the sky (the sun is during the day and a star called Sirius is during the night). The reason the North Star is important, is that the imaginary axis that the Earth spins around points out into space and there just happens to be a star very close to where the axis is pointing. If it stayed dark for 24 hours, you could watch the Big Dipper go completely around the North Star.

alt : test.mov

Fig 2: Starting in the early evening on a winter night, the Big Dipper makes a complete circle around
Polaris in 24 hours. The stars are 'still' up there even during the day!

Where would the North Star be in the sky if you were standing at the North Pole? the Equator? the South Pole?

animation of Polaris' altitude as latitude increases
Fig 3: As you move North from the Earth's equator (0° N), the apparent altitude of
Polaris (the end star in the handle of the Little Dipper) also increases.

If you were standing at the North Pole, then the North Star would be directly over head and the stars would never rise or set.

If you were at the equator, then the North Star would be on the northern horizon. From the equator you can see all the stars that are visible from Earth rise and set.

If you were at the South Pole, the North Star would not be visible because it would be under your feet. So is there a South Star? Unfortunately, no. It is just a coincidence that the North Star is in the sky near where the axis points. In fact, Polaris, is not always the North or Pole star. Because of something called precession, Earth weeble wobbles extremely slowly as it spins so that the Earth's axis actually points to different parts of the sky over time.

Okay, we found the North Star, let's move on!

<-- PREVIOUS     NEXT -->

Updated: 30-Jul-2013