What should you photograph tonight?
Pick your location, your telescope and your camera. The planner works out tonight's real darkness window, follows each of 411 popular deep-sky targets across the sky, checks where the Moon is, and ranks what will look best in your frame, with the reason for every pick.
How the ranking works
Every target gets a score out of 100 from four simple parts. Nothing is hidden: open any target to see its four part-scores.
Time (40%): hours the target spends above your minimum altitude while the sky is fully dark. Five hours or more gets full marks; how high it climbs adds a little.
Framing (25%): how much of your frame the object spans when you rotate the camera to suit it. Between 30% and 90% is ideal. Tiny objects score low, and objects bigger than the frame lose points because they need a mosaic.
Brightness (20%): for objects larger than 3′ we use surface brightness (how bright each patch of the object is) adjusted for your focal ratio, because a faster scope (smaller f-number) builds up faint nebulae quicker. Emission nebulae and supernova remnants get one magnitude of credit for the hydrogen-alpha light cameras record. For small objects we use total magnitude adjusted for your aperture.
Moon (15%): a bright Moon that is up during your usable time lowers the score, most of all when it is within 30° of the target, but still noticeably when it is far away, because moonlight brightens the whole sky. Emission nebulae lose only half as much, because narrowband filters cut most moonlight.
The month view adds up, night by night, the usable hours multiplied by the Moon part, then combines that (45%) with framing (30%) and brightness (25%).
Accuracy and data
All positions come from astronomy-engine: twilight times from the Sun's real altitude, catalogue positions precessed from J2000 to the night's date, and standard atmospheric refraction. We check these numbers against Telescopius, the US Naval Observatory and Stellarium.
Targets: 411 objects. Positions, sizes and brightness come from OpenNGC by Mattia Verga (licensed CC BY-SA 4.0), combined with a hand-checked list of favourite imaging targets (Sharpless nebulae, the Horsehead, galaxy groups) that uses imaging sizes from the SEDS Messier database, Sharpless (1959) and SIMBAD. Our trimmed target list is shared under the same CC BY-SA 4.0 licence.
Brightness for faint, patchy nebulae is an estimate from catalogue magnitudes. The score is a planning aid, not a promise: local light pollution, weather and your filters matter too.
Questions
What is astronomical darkness and why does it matter?
It is the part of the night when the Sun is more than 18° below the horizon, so twilight no longer brightens the sky. Faint galaxies and nebulae show best then. Near midsummer at high latitudes it may not happen at all; the planner then falls back to nautical darkness (−12°) and tells you.
Why does my telescope change the list?
Your focal length and sensor decide how big the frame is on the sky. A wide refractor suits big nebulae like the North America Nebula; a long-focus telescope suits small galaxies and planetary nebulae. The planner ranks targets that fill your frame well higher.
How far from the Moon should I stay?
For galaxies and reflection nebulae, more than 90° from a bright Moon is a good rule. Emission nebulae shot through narrowband filters tolerate the Moon much better. Use the Moon filter to hide targets too close to it.
What minimum altitude should I use?
30° is a sensible default: lower than that you look through much more air, which blurs and dims the image. Raise it if trees or buildings block your view, or lower it if your horizon is clear and you want more targets.
Is my equipment saved?
Yes, in your own browser only. The planner remembers your telescope, camera and location on this device, and other OrbitaSky tools can use them too.