How do I use a star chart or app to find objects?
Getting oriented
A star chart (printed or digital) shows the sky as a map. To use it, first determine which direction you're facing and the date/time. Most apps use your phone's GPS and gyroscope to show the sky in real time—just hold your phone up and it labels stars and planets. Printed charts require you to rotate the map to match your view; hold it overhead with the direction you're facing at the bottom.
Start by finding a few bright, easy constellations like the Big Dipper, Orion, or Cassiopeia. These serve as signposts. Once you recognize them, you can use them to locate other stars and objects. This method is called star-hopping: you move from a known bright star to a nearby target in small steps.
Star-hopping and using setting circles
To star-hop, look at your chart and identify a pattern of stars leading to your target. For example, to find the Andromeda Galaxy (M31), start at the Great Square of Pegasus and follow two stars to the left. Use your telescope's finder scope (a low-power sight) to center the starting star, then move in the direction indicated by the chart, checking the view through a low-power eyepiece.
If your telescope has setting circles (manual or computerized), you can use celestial coordinates (right ascension and declination) from an app to point the scope. Computerized GoTo mounts do this automatically after alignment. For manual scopes, setting circles are less common on beginner models, but you can still use them if you learn to read them.
- Use an app with augmented reality to identify objects by pointing your phone
- Start with bright constellations as landmarks
- Star-hop in small steps from a known star to your target
- Use a finder scope to center the starting star
- For GoTo mounts, align with two or three bright stars first
Common mistakes
- Trying to use a star chart without adjusting for date and time—the sky changes throughout the year.
- Forgetting to account for your latitude; charts are often made for specific latitudes.
- Using a red light to read charts is good, but a white light will ruin your night vision.
