How to Use the Milky Way Season Planner
Pick a month and a night, aim a simulated camera at the galactic core, and save a shot card for the field.
Open the Milky Way Season Planner
What this tool answers
- Which months put the galactic core in a dark sky from my Guyana site?
- Which nights in that month score best, and when does the core peak?
- Where do I point my camera and lens so the core lands in the frame?
For the why behind the season, read Milky Way Season Near the Equator.
What you see on the screen
On a computer the settings sit on the left and the Camera viewfinder on the right. On a phone the viewfinder comes first; tap the Light pollution and Date headings to open those sections.
- Camera & lens: Camera body (six presets, Sony A7 III by default), Focal length (mm) and Aperture (f/).
- Location: ten Guyana towns, one per region. There is no GPS button.
- Light pollution: Bortle source (automatic, or Manual override with a 1 to 9 slider), plus Show light pollution and Show moon switches.
- Date: Preview date.
- Season (Guyana): twelve month buttons, each with a score from 0 to 100.
- Camera viewfinder: the simulated sky for your lens, with a caption that reads GC in frame, GC outside frame or Core below horizon.
- Six readouts: Cam Az, Cam Alt, GC Alt, GC Az, Frame (Yes or No) and Moon (percent lit).
- Shot card and Field guide panels, then the Preview time wheel with the Bore azimuth and Bore altitude dials.
- Camera & core details: field of view, Sun and Moon, sky darkness, and the core's Peak tonight and Hours above 15°.
- Best nights in (month name): a calendar with a score on each day, below everything else.
Step by step
- Set Camera body, Focal length (mm) and Aperture (f/).
- Choose your site in Location (Georgetown is the default).
- In Season (Guyana), tap a month. The Preview date jumps to the 15th.
- In the Best nights calendar, tap a day to open its night panel.
- Read the Moon rows, then tap Use this night. The planner sets that date, moves Preview time to the core's highest point and turns Show moon on.
- Drag the viewfinder, or turn the dials, until Frame reads Yes.
- Slide the Preview time wheel to test other times. It snaps to 5 minutes.
- Tap Save shot card, untick any lines you do not need, then tap Download PNG.
- Tap Open field guide to carry the site, date, time and camera into the Milky Way Field Guide.
- A day or two before, check cloud in Stargazing Weather or Tonight Observing Score.
The real Milky Way Season Planner, step by step: the light-pollution warning, the 2027 month scores from Georgetown, June's best night, and Use this night.
How to read the results
Month scores rate one night, the 15th, by how high the core climbs and how many hours it stays at 15° or more during astronomical darkness (Sun more than 18° down). They ignore the Moon, so they show the season, not a particular night. Grades: Excellent 75 or more, Good 50 to 74, Fair 25 to 49, Poor below 25. Full height credit needs a core near 75° altitude, and the core peaks at 54° to 58° here, so Good (about 60) is the best month grade from Guyana. At Georgetown in 2027, March to September grade Good, February and October Fair, and November to January Poor.
The planner's twelve month buttons for Georgetown or Lethem, each score split into its height and hours parts.
Day scores use the same grades: half Moon, 40% core height and hours, 10% dark window length. If the core never reaches 15° in the hours scored, the day is capped at 35 and drawn faded with "CP" (Core poor).
The night panel shows:
- Moon: Phase, Illumination, Washout (worst) and Moon-GC separation.
- Galactic core: Max altitude, Best local time and Hours above minimum (hours at 15° or higher in astronomical darkness).
- Dark window: Duration, the longest stretch with the Sun 18° or more below the horizon and the Moon down.
- Why this rank: one or two plain reasons.
Washout (worst) is how much the Moon brightens the shot during the core hours, and it is the larger of two numbers. The first is the Moon in your frame: its full lit share when it is inside the frame, fading to nothing 45° from where the camera points, so it depends on your aim and lens. The second is the Moon anywhere in the sky: its lit share times the share of the core hours it is above the horizon. A full Moon that is up for all the core hours therefore washes out the night whichever way you aim. When the Moon is up all night, Duration shows a dash.
The best-nights calendar and its night panel, run on the planner's own code, with the camera aimed south, east or west.
A June night's panel reads Illumination 98% and Duration -. You plan to aim away from the Moon. What grade should you expect?
- Good, because the Moon is behind the camera
- Poor or Fair, because the Moon is up for the core hours and lights the whole sky (the right answer)
- Excellent, because June is the best month
- It depends on the Bortle setting
Washout is at least the Moon's lit share times the share of the core hours it is up, wherever the camera points. A 98% Moon that is up all night gives a washout near 98%, which takes away almost all of the Moon half of the score. Duration shows a dash because the Moon is up through the whole dark night.
Bortle settings change the picture and the shot card, not the scores. At Bortle 7 or brighter a dialog, "Milky Way not visible here", offers Keep local sky or Simulate dark sky.
Planner times are local solar time from longitude, not clock time. At Georgetown, planner 22:00 is 21:53 Guyana time (America/Guyana, UTC-4); at Lethem the gap is under a minute.
Planner time as Guyana clock time for the ten planner towns.
The planner says the core peaks at 22:00 from Georgetown. What does your phone read at that moment?
- 21:53 (the right answer)
- 22:00
- 22:07
- 23:00
Planner times are local mean time: the clock for your own longitude, without the equation of time. Georgetown sits about 1.8° east of 60° W, the meridian Guyana's clock keeps, so the planner runs about 7 minutes ahead: planner 22:00 is 21:53 GYT.
Using it from Guyana
- The core crosses due south at 54° from Georgetown and 58° from Lethem. Keep Bore azimuth near 180° and raise Bore altitude near the peak (the default aim is 180° and 25°).
- Core season runs February to October: before dawn from February to May, most of the night in June, evenings from July to October.
- From November to January the core is not up in dark hours. Open the Field Guide for the winter Milky Way and the Magellanic Clouds.
- Bartica, Mahdia, Lethem and Mabaruma carry a "dark sky" tag. See Dark Skies in Guyana.
A simulated viewfinder: turn the dials until Frame reads Yes.
What it does not do
- It has no weather data. It weighs the Moon, but not the clouds.
- It has no GPS and no box for your own coordinates.
- It knows nothing about hills, trees or buildings on your horizon.
- It gives no shutter or ISO advice. The Field Guide PDF does.
Common mistakes
- Trusting a Good score near full Moon without reading Illumination and Duration.
- Reading planner times as clock times.
- Ruling out a month from its button score without opening the calendar.
- Treating the simulated sky as the naked-eye view from a bright town.