Most telescopes work well for daytime viewing as well as for astronomy. If you have a refractor or a catadioptric telescope (the Schmidt-Cassegrain is the most popular example), and you would like to use it for terrestrial observations, the most useful additional accessory you can buy is an erect-image diagonal.If you look through your telescope with the standard mirror or star diagonal installed, you will notice that objects may be either upside down, flipped so that you see a mirror image, or a combination of the two. This is fine for observations of celestial objects, but it can be a little confusing when you are trying to track a boat as it moves through the water, or an eagle as he flies towards his perch.Luckily, this is an easy problem to correct. Simply remove the standard diagonal from the telescope\'s focuser or visual back, and install the Celestron 45