About FindFrame
Find the spot to stand and the minute to be there for the shot where the Moon, Sun or a planet lines up behind a landmark.
A full Moon rising exactly behind a cathedral spire looks like luck. It is not. It is a geometry problem with a small number of correct answers, and each answer is a specific position on the ground and a specific minute. FindFrame solves that problem from the picture backwards: describe the shot you want, and it returns the places and times that produce it.
Using the planner
- Pick a subject — a landmark, or any point you drop on the map.
- Choose the body and the window: Moon, Sun or a planet, over the next days, weeks or months.
- Say how big it should be in frame. This is what fixes your distance, and it is the step people skip. The Moon is about half a degree across; making it loom behind a spire means standing a long way back with a long lens.
- Read the solutions. Each gives shooting coordinates, the time to the minute, bearing and altitude, the focal length that frames it, and the phase on the night.
- Check the horizon profile for that position before committing. A moonrise listed for 19:42 may not clear a ridge until 19:58.
What the numbers are built on
- JPL DE421 ephemeris for Sun, Moon and planet positions, at sub-arcminute accuracy over any period you would realistically plan for.
- Topocentric correction. Raw ephemeris positions are geocentric. Because the Moon is close, an observer on the surface sees it displaced by up to a degree — two full Moon diameters. Ignore that and the alignment misses the building entirely.
- Atmospheric refraction, which lifts bodies roughly half a degree at the horizon. For a rise behind a distant landmark this is the difference between clearing the roofline and not.
- Horizon raycasting against terrain elevation and building heights, so the altitude at which a body becomes visible reflects what is actually in the way from where you stand.
Honest limitations
Vegetation is not modelled. A line of mature trees costs several degrees and appears in no building dataset. Elevation models have finite resolution, so complex urban skylines are approximated. Refraction depends on the real temperature and pressure profile on the night, which is the largest genuine uncertainty in any horizon shot. Scout the position in daylight when the shot matters.
Aircraft transit predictions use live ADS-B data from the OpenSky Network. Coverage has gaps at low altitude and the projection assumes aircraft hold course, so treat them as a strong hint about where to point, not a schedule.
In the field
- Arrive at least fifteen minutes early and navigate by the coordinates, not the description. Metres matter.
- Expose for the Moon, not the scene. A lit Moon is roughly a daylight exposure; metering for the landmark turns it into a featureless white disc.
- Shoot a burst — the disc moves visibly between frames.
- Check the horizon cloud forecast, not just the general one. Low cloud kills horizon shots under an otherwise clear sky.
Read more
Our full guide works through the geometry of an alignment, why parallax and refraction matter so much near the horizon, and how to plan a season ahead rather than a week.