Three things determine when to head out — and one of them changes every night.
The best time to stargaze tonight is after astronomical twilight ends (sun 18° below the horizon), when the moon is below the horizon, during the clearest weather window. For most locations, this means the darkest hours between late evening and early morning. The exact window shifts every night as the moon's schedule changes and weather moves through. Clear Skys calculates the precise best viewing window for your location automatically — check your forecast to see tonight's.
The most common beginner mistake is heading out too early. Sunset feels like the starting gun, but usable stargazing doesn't begin for another hour or two — sometimes longer. The gap between sunset and a properly dark sky is real, and it costs you if you don't account for it.
Three factors determine the best time to observe on any given night: when astronomical darkness begins, when the moon rises or sets, and when the weather is clearest. The sweet spot is where all three overlap — and that window can be surprisingly narrow. On a good night it might last six hours. On a bad one, you might get ninety minutes.
Clear Skys calculates this automatically. Every forecast identifies your best viewing window — the longest continuous run of high-scoring hours — so you know exactly when to set up and when to pack away. But understanding what drives that window helps you make better decisions, especially when conditions are marginal.
After the sun sets, the sky passes through three phases of twilight before reaching full darkness. Each phase is defined by how far the sun sits below the horizon, and each determines what you can see.
Civil twilight ends when the sun reaches 6° below the horizon — the sky is still noticeably bright, and only Venus or Jupiter might be visible. Nautical twilight ends at 12° below — bright stars and major constellations appear, and you can start observing planets through a telescope. Astronomical twilight ends at 18° below — this is when the sky is as dark as it gets, and faint objects like galaxies, nebulae, and the Milky Way become visible.
The time from sunset to astronomical darkness varies by latitude and season. In midwinter from the UK, it's about 90 minutes. In midsummer, astronomical darkness may not arrive at all — the sun never drops far enough. Near the equator, the transition is fast — often under an hour — because the sun drops almost vertically below the horizon.
The practical takeaway: don't arrive at sunset and wonder why you can't see anything. Check when astronomical darkness begins at your location — Clear Skys shows this in every forecast — and plan to be set up and dark-adapted by then.
Why it doesn't get dark in summer →After cloud cover, the moon is the single biggest variable affecting what you can see. A bright moon above the horizon floods the sky with scattered light, washing out everything except the brightest stars and planets. The difference between a moonlit sky and a moonless sky is the difference between seeing a few dozen objects and seeing hundreds.
The key isn't just the moon's phase — it's when the moon is above your horizon relative to your darkness window. A 70% illuminated moon that sets at 11pm is far less damaging than a 40% moon that's up all night. The hours after moonset (or before moonrise) are your premium dark-sky time.
This is where timing gets tactical. In the days after new moon, the crescent moon sets early in the evening — often before astronomical darkness even begins. That gives you the entire night with dark skies. In the days after full moon, the moon rises later and later each night, so your dark window is the first few hours after darkness starts, before moonrise. Around full moon itself, the moon is up most of the night and deep-sky work is largely a write-off.
Clear Skys calculates the overlap between moon and your darkness window automatically and subtracts a proportional penalty from the score. When you see a best viewing window of "23:00–03:00" on a night with a late-rising moon, that's the app telling you: these are your moonless hours — use them.
How the moon penalty works →Weather doesn't stay constant through the night. A clear evening can cloud over by midnight, or an overcast start can break up after 1am. Hourly variation is the norm, not the exception — and it's why a single "tonight's weather" check at 6pm is unreliable for planning a session that might run until 3am.
Clear Skys scores every hour of the darkness window independently, using four weather factors: cloud cover (55% of the score), wind speed (20%), humidity (15%), and rain probability (10%). The best viewing window is the longest consecutive stretch where all four factors are favourable.
In practice, some common patterns are worth knowing. High-pressure systems produce the clearest, calmest nights — look for rising barometric pressure in the afternoon. Cold fronts can bring excellent transparency (the air is unusually clear after the front passes) but also gusty wind. Radiation fog forms after midnight on calm, clear nights and can reduce visibility near ground level while the sky overhead remains perfect.
The 7-day forecast lets you compare nights and pick the best one of the week rather than gambling on tonight. A score of 75 on Wednesday is worth waiting for if tonight is 45.
The best time to stargaze tonight is where three windows overlap: astronomical darkness, moonless sky, and clear weather. Here's how that looks in practice.
On a perfect night — new moon, clear all night — your window is simply astronomical darkness start to astronomical darkness end. That might be 11pm to 4am in summer or 6pm to 7am in winter. You have maximum flexibility and can observe whenever suits you.
On a typical night, the window is narrower. Say astronomical darkness starts at 10:30pm, the moon rises at 1:15am, and clouds are forecast to move in after 2am. Your best window is 10:30pm to 1:15am — about three hours. That's still plenty for a good session, but you need to be set up and dark-adapted by 10:30, not arriving at 10:30.
On a marginal night, you might have only a 90-minute gap between cloud clearing and moonrise, or between moonset and dawn. Whether that's worth going out for depends on what you're doing — a quick planetary session or ISS pass needs 15 minutes, while deep-sky astrophotography needs two hours minimum.
This is exactly what the Clear Skys best viewing window tells you. When the forecast says "Best: 22:30–01:15 (3h)" with a score of 72, you know the window, you know the quality, and you can make an informed decision.
Different objects have different requirements, and knowing what you're after changes when you should head out.
**The Milky Way** needs the darkest possible sky — astronomical darkness with no moon above the horizon. From the UK, the galactic core is best placed between August and October, looking south between 11pm and 2am. Any moonlight destroys the contrast. This is the most demanding target in terms of timing.
**Planets** are the most forgiving. Venus, Jupiter, and Saturn are bright enough to see in twilight, so you can start observing 30 minutes after sunset — no need to wait for full darkness. Planetary detail through a telescope (cloud bands, rings, polar caps) actually benefits from the steadier atmosphere that often comes early in the evening before radiative cooling creates turbulence.
**The ISS and bright satellites** are only visible around dusk and dawn, when the satellite is in sunlight but your sky is dark. In summer from the UK, this window extends through most of the short night. In winter, you'll only catch passes in the first couple of hours after sunset or before sunrise.
**Aurora** requires darkness but not necessarily full astronomical darkness — the glow is bright enough to see against deep twilight at high latitudes. The key timing factor is geomagnetic activity, which peaks unpredictably. When an alert fires, get outside as quickly as possible — aurora displays can fade within minutes.
**Meteor showers** peak after midnight because the Earth's rotation turns your location into the "leading edge" that sweeps through the debris stream. Rates typically double between midnight and 4am compared to before midnight. A moonless post-midnight window is the ideal.
**Deep-sky objects** (galaxies, nebulae, star clusters) need full darkness and no moon — the fainter the object, the more critical this is. Observe your faintest targets first when the sky is at its darkest, and work toward brighter objects as conditions change.
Arrive 30 minutes before your best window starts. You need time to set up equipment, let your eyes dark-adapt (20–30 minutes with no artificial light), and get comfortable. If the window starts at 11pm, be there at 10:30.
Don't check your phone. Every glance at a bright screen resets your dark adaptation and you'll miss the faintest objects for the next 20 minutes. Use a red-light app or tape red film over your torch if you need to see your star chart.
Face away from light pollution. If there's a town glow on one horizon, observe toward the opposite side. The zenith (straight up) is always the darkest part of the sky.
Start with the targets that need the darkest sky. If you want to see the Milky Way, a faint galaxy, or a dim nebula, observe them first while the sky is at its darkest — before any moon rise, before any cloud encroaches. Save bright targets like planets, double stars, and star clusters for later when conditions may not be as pristine.
If conditions are marginal (score 45–60), it's still often worth going out. You might not get textbook conditions, but planets, the moon, and bright deep-sky objects like the Orion Nebula and Andromeda Galaxy are visible even in imperfect skies. Check the forecast — if there's a usable window of two hours or more, there's something worth seeing.
Clear Skys calculates the best viewing window for any location worldwide — when to go out, how long you've got, and what the conditions will be like. Search your location or check one of these forecasts:
Check tonight's stargazing conditions for any location worldwide.
Search your location →The best time is after astronomical darkness begins, when the moon is below the horizon, and when cloud cover is lowest. This changes every night. Clear Skys calculates your exact best viewing window — the longest stretch of good conditions — for any location.
Planets and bright stars are visible about 30–45 minutes after sunset. For deep-sky objects (galaxies, nebulae, the Milky Way), you need to wait for astronomical darkness — when the sun is 18° below the horizon. This takes 75–120 minutes after sunset depending on latitude and season.
Significantly. A bright moon washes out faint objects and can reduce visible meteors and deep-sky targets by 60–80%. The best deep-sky nights are within a few days of new moon. Planets and bright stars are unaffected by moonlight.
Often yes. A score of 45–60 still offers usable windows for planets, bright deep-sky objects, and the moon. Check the best viewing window — even a two-hour gap of decent conditions is enough for a rewarding session. Only scores below 30 are genuinely poor.
By midnight, astronomical darkness is well established, early-evening cloud and moisture often clears as the air cools and stabilises, and any waxing moon has usually set. For meteor showers specifically, rates increase after midnight because Earth's rotation turns your location into the debris stream. The hours from midnight to 3am are statistically the darkest, calmest, and most productive.