RigTonightHow to read RigTonight's astrophotography forecast and plan your night
The Tonight tab answers two questions: is it worth setting up, and what should you point at? This tutorial takes you from an empty page to a plan.
1. Set your location
Under Where are you shooting from?, type a town, address, park or dark-sky site and pick it from the list. You can also click Use my current location, or Enter coordinates instead if you know your latitude and longitude. Give the site a name, such as "Backyard", and save it.
Your site stays in your browser. The weather service only receives your position rounded to about 1 km.
2. Tell it how dark your sky is
Set Light pollution to your site's Bortle class, from 1 (excellent dark site) to 9 (inner city). It lowers every hour's score at bright sites, so a clear night in a city doesn't look as good as a clear night in the countryside. If you don't know your class, a light pollution map will tell you. The Bortle scale explained shows what each class looks like.
3. Choose a minimum altitude
Min altitude (20°, 30° or 40°) is how high a target must be before it counts. Low targets shine through more air, haze and light pollution. 30° is a sensible default. Raise it if trees or houses block your horizon; lower it from a dark site with a clear horizon.
4. Read the night summary
A banner gives the Best window: the stretch of clear, dark hours worth setting up for. Below it you'll see sunset and sunrise, the dark window, the moon and your light pollution. If the sun doesn't go far enough below the horizon, as in high-latitude summers, Tonight says so.
5. Read the hourly strip
Each column is an hour of the night. From top to bottom:
- Overall score combines cloud, darkness, moon, seeing, transparency and light pollution into one number up to 100, banded poor, fair, good or great. Cloud matters most; the rest trim the score.
- Weather: cloud cover from each of five models (ECMWF, GFS, ICON, GEM and the UK Met Office) on its own row. When they agree, trust the forecast more. When they disagree, expect surprises. See Which weather model should astronomers trust?.
- Darkness: twilight fading into full astronomical darkness.
- Moon: whether it's up, and how bright.
Hover over any hour for a plain-English summary of it, and over a model's name to learn what it is.
6. Pick a target
Best targets tonight ranks objects by clear, dark, moon-free time above your minimum altitude. With a rig built on the Rig tab, it also weighs how well each target fills your field of view and suits your filters. The first one is marked Top pick. Narrow the list to Nebulae, Galaxies or Star clusters if you have something in mind.
Each target's label (Great for your rig, Good for your rig or Not ideal for your rig) explains itself when you hover over it: too small for your field, needs a mosaic, or a filter that suits it.
Click a target for its detail panel: when it's photographable tonight, its highest altitude, the moon's distance from it, an altitude chart through the night, and a sky preview with your camera's frame drawn on it.
Why the moon matters more for some targets
A bright moon washes out galaxies and reflection nebulae, but dual-band and narrowband filters cut most moonlight from emission nebulae. That's why the ranking changes with your filters. Astrophotography and the moon explains when you can still shoot.
Next: browsing the whole catalog and checking how targets frame with your camera.