January 8, 2021
How do skywatchers measure distances in the night sky? Here’s how to understand it when they speak of objects as being several degrees (or several arc minutes or arc seconds) apart.
Use this “handy” guide to measure degrees on the dome of the sky. Image via Fort Worth Astronomical Society.
The handiest measuring stick for the sky’s dome is the one on the end of your arm. You can use the width of your pinky, fist and more to gauge the distance between sky objects. That comes in handy when you’re observing conjunctions between planets, or close planets and stars, or planets and stars and the moon, plus many other space objects. You’ll often find these objects described as being a certain number of degrees, arc minutes or arc seconds apart.