To do it, you'll need a dark sky, a bright star in it, and your telescope! With your telescope, focus on a star that's very bright, such as Sirius. ... Basically, this refers to circles around the star that might look a little wiggly. If the circles you see are not concentric, then your telescope needs to be collimated.

What happens if you don't collimate your telescope?

If your telescope is not properly collimated, it will be impossible to properly focus, no matter the sky conditions.

Which telescope does not need collimation?

Refractor telescopes are permanently collimated at the factory and therefore should never require collimation. In general, reflector telescopes are prone to go out of collimation, especially when carried in your car.