AstroTonight
Plan astrophotography nights
AstroTonight ranks the galaxies, nebulae, star clusters and planets above you by how well they’ll image tonight, from your location, your sky’s darkness, your skyline and your telescope.
Need help? Email nzvman75@icloud.com. It helps to include your iPhone model, your iOS version and, if you can, a screenshot.
Common questions
Why does AstroTonight need my location?
To work out which targets are above you and when, and to help the compass find true north in the camera view. Your location stays on your iPhone. If you’d rather not share it, choose Enter Coordinates and type in your site’s latitude and longitude.
What is a Bortle class, and which one should I choose?
The Bortle scale rates how dark your sky is, from 1 (a truly dark site) to 9 (an inner-city sky). AstroTonight uses it to decide which targets are easy or hard from where you are. If you’re not sure, edit your site on the Sites tab and tap Not sure? Look up your site on lightpollutionmap.info. If you own a sky quality meter, turn on I have a sky quality meter reading and enter it instead.
How do I map my skyline?
- Stand where you set up your telescope, ideally at dusk or in daylight so you can see the trees and roofs.
- Open the Skyline tab and tap Map the Skyline with the Camera.
- Point the crosshair at the top edge of the trees or roofline, hold the red button and turn slowly, keeping the crosshair on the skyline.
- Where the sky is clear down to the horizon, trace along the white horizon line.
- Use Erase or Undo to fix mistakes, then tap Save.
Gaps of up to 30° are filled in automatically, and anything you haven’t mapped is treated as open sky.
The camera view points the wrong way
iPhone compasses can be thrown off by metal tripods, cars and magnetic phone cases. First, move your iPhone in a figure-of-eight to calibrate it. If it’s still off, tap Align in the camera view, pick a bright star, planet or the Moon that you can see, put it in the middle of the crosshair and tap Align. You can reset the correction in Settings.
Why is a target marked “Very hard”?
Difficulty compares how bright the target is with your sky. A bright Moon nearby, twilight or a light-polluted site all make faint targets harder. Open the target to see why. For emission nebulae, turning on I use a narrowband or dual-band filter in Settings makes a big difference, since those filters cut through light pollution and moonlight.
Why does the list show tonight when it’s daytime?
Nothing can be imaged while the Sun is up, so during the day the Tonight button shows how things will look once it gets dark. It switches to live after sunset. To look at any other time, tap Plan a time.
Can I use my own telescope?
Yes. Go to Settings → My Telescopes → Add Telescope and enter its focal length and aperture, plus your camera’s image size in pixels and pixel size. It then appears under the name you give it, and every target shows how it fits your frame. The Seestar S30, S30 Pro, S50 and S50 Pro are built in.
How do I turn on night mode?
Go to Settings and turn on Night mode (red screen). The whole app turns red to protect your night vision at the telescope.
Where are my sites, skylines and images stored?
Everything stays on your iPhone and is included in your iPhone’s normal backups. AstroTonight has no account and doesn’t send your data anywhere. Deleting the app removes everything it stored. See the privacy policy for details.
Does it work without an internet connection?
Yes. Everything is calculated on your iPhone, so it works in a dark field with no signal.