Milky Way planner
An honest estimator for when the galactic core is worth chasing: astronomical darkness, how long the core sits above a minimum altitude, the moon’s brightness, and a plain-language season verdict for any date and place.
Date, location & angle
North positive (e.g. Boulder CO 40.0°N).
East positive, west negative (e.g. Boulder -105.3°W).
Higher is safer: the core is best when it clears low haze, trees and horizon glow.
Location permission is only requested after you click the button. Times are shown in your device’s time zone.
Core estimator
How the estimator works
The planner tracks the galactic-centre region (right ascension 17h45m, declination −29°) - the brightest, densest part of the milky way. For the night around your selected date it counts the minutes when the sky is astronomically dark (sun more than 12° below the horizon), and of those, the minutes when the core region is above your chosen minimum altitude. The ratio of those two numbers is shown as a percentage, and the moon’s illumination is reported separately so you can judge how much of that geometric opportunity survives moonlight.
Read the result as an estimator, not a forecast. Exact core rise/set times, moonrise and moonset, and the moon’s position in the sky are not modelled, and those details genuinely change the best hours on a specific night. Before travelling, confirm the night with a star chart or planetarium app such as Stellarium, SkySafari or PhotoPills.
Approximate core season (mid-northern latitude, ~40°N)
The table below is a rough guide for the northern hemisphere. Actual dates shift with your latitude - further south extends the season; further north shortens and lowers it - and the moon decides whether any given night is usable.
| Months | Core in the night sky |
|---|---|
| November – February | Weak - the core is below the night horizon for most mid-northern latitudes. Skip. |
| March – April | Core rises during the night - visible low in the east after midnight. |
| May | Core well up in the after-midnight sky. |
| June – July | Best core nights - the centre is high around midnight (though summer nights are short at high latitude). |
| August | Core high in the evening, setting around or just before midnight. |
| September – October | Core visible early evening, low and brief - the season is fading. |
Example
For Boulder, Colorado (40.0°N, 105.3°W) on 20 June the estimator reports about 6 h 31 min of astronomical darkness with the core above 10° for roughly 90% of that dark time - a classic summer verdict of the core sitting high around midnight. Compare 20 December, where the sky is dark for over 12 hours but the core never rises, giving a “not a core night” result. Moon phase moves the practical verdict on any of these nights.
Practical reading of the moon row
- Below roughly 40% illumination the moon is usually a mild factor - plan for the moon to be down or behind you.
- Between about 40–70% the sky still darkens but the core loses contrast.
- Above roughly 70% illumination the core is largely washed out even when geometrically high.
Related tools
Check the moon phase calculator for the surrounding dark windows, dial in a safe shutter length with the astro exposure calculator, and see the golden hour calculator for the warm-light end of the same night.
Frequently asked questions
What exactly does this tool estimate?
For the night around your chosen date and location it estimates three things from the standard solar and lunar formulas: how many minutes the sky is astronomically dark (sun more than 12° below the horizon), what percentage of that dark time the galactic core region stays above a chosen minimum altitude, and how bright the moon is. It then turns that into a plain-language verdict.
Where is the milky way core in the sky?
This planner tracks the galactic-centre region, which sits near right ascension 17h45m and declination -29°. Because the Earth turns and moves around the sun, that region rises and sets over the year - in the northern mid-latitudes it is best placed in the summer months and is out of the night sky from roughly November to February.
How accurate is the "visible in the evening / after midnight" verdict?
It is a geometric estimate to within about half an hour, based on where the core is relative to your local midnight. Exact rise and set times, moonrise and moonset, atmospheric clarity and light pollution are not modelled, so always verify a specific night with a star chart or planetarium app before travelling.
Why does the moon matter so much?
The milky way core is faint. Below roughly 40% illumination the moon is a mild factor; above about 70% its scattered light washes the core out even when the core is geometrically high in the sky. This planner shows the moon separately so you can judge whether a geometrically good night is practically usable.