When you're getting ready to look at the stars with a telescope, it's important to know a few key features. This will help you pick the right one. Here are the three main things to think about: aperture, focal length, and magnification.

1. Aperture: This is the opening in the telescope that lets light in. A bigger aperture means more light comes through, which gives you clearer and brighter pictures of stars and planets. If you're just starting out, a good size is at least 70mm for refractor telescopes or 114mm for reflector telescopes. For example, a telescope with a 100mm aperture can gather more than twice as much light as a 70mm telescope. This can really help you see fainter stars and objects in the sky.

2. Focal Length: This is the distance from the lens or mirror to the point where the light comes together. It affects how much the telescope can make things look bigger. A longer focal length usually means more magnification, which is useful for looking at faraway planets. For instance, if a telescope has a focal length of 1000mm, it will make objects look bigger than one with a 500mm focal length, using the same eyepiece.

3. Magnification: This explains how much bigger an object looks compared to seeing it with just your eyes. You can figure out the magnification using this simple formula:

   $\text{Magnification} = \frac{\text{Focal Length of Telescope}}{\text{Focal Length of Eyepiece}}$

   For example, if you use a telescope with a 1000mm focal length and a 10mm eyepiece, you would get:

   $\text{Magnification} = \frac{1000}{10} = 100 \text{x}$

By knowing these important features, you can pick a telescope that fits your stargazing needs and helps you see the wonders of the sky!