Sky Tonight
What is visible tonight from your location — planets, the Moon, bright stars and passes — computed from real positions rather than a generic list.
🛰️ International Space Station · live
“Full Moon” here is a label covering 3.69 days. The full moon lasts an instant.
The moon's cycle is 29.530588853 days and this page cuts it into 8 equal bands of 3.6913 days apiece. Every gap between the published boundaries is identical, and the first sits at half a band — so each name is centred on the moment it describes rather than starting at it. Four of the eight names are shapes and four are instants. A waxing crescent really is a waxing crescent for days. New, First Quarter, Full and Last Quarter are moments — the moon is exactly half lit for no time at all — and each gets a 3.69-day band anyway, so the label can sit up to 1.85 days from the event it names.
| Age (days) | Illumination at that boundary |
|---|---|
| 1.85 | 4% |
| 5.54 | 31% |
| 9.23 | 69% |
| 12.92 | 96% |
| 16.61 | 96% |
| 20.3 | 69% |
| 23.99 | 31% |
| 27.68 | 4% |
The percentage beside the name is not banded. It comes from the actual angle, so it moves continuously and reaches 100% only at the instant of full. At both edges of the Full Moon band it reads 96%, and at both edges of the New Moon band 4% — mirror images, as they should be. Read the name as “nearer to full than to anything else” and the number as the real answer.
The wraparound is the part that usually breaks, and it holds
New Moon is the only name in two pieces: ages from 27.68 to 29.530588853 belong to it just as much as ages from 0 to 1.85. Those two pieces are 1.85 and 1.85 days, adding to 3.70 — the same width as every other band. A phase table that forgets the wraparound reports the three days before a new moon as a waning crescent and then jumps. Sweeping the whole cycle at one-hundredth-day resolution reaches all 8 names and nothing else, and dates before the January 2000 reference still give an age inside the cycle rather than a negative one.
One limitation the arithmetic cannot show. 29.530588853 days is the mean cycle; the real interval between new moons varies by several hours because both orbits are ellipses. A phase computed from a mean and a fixed epoch drifts against the sky by up to about 0.5 of a day — 14% of a band, so it changes the answer only near a boundary. Which is to say the percentage is more precise than it is accurate, and that is the right trade for arithmetic needing no ephemeris and no network call.
And the station's distance now counts the 420 kilometres of altitude
The panel above reported the distance along the ground between you and the point the station was over, which is not the distance to the station. The ISS orbits about 420 km up, so when it passes directly overhead the ground distance is zero and the real distance is 420 km — the understatement is largest exactly when the number matters most. It is above your horizon only out to roughly 2,250 km of ground track, and across that whole visible range the ground figure was short by between 420 and 99 km. It now computes the straight-line range from the reported altitude, so the number under “distance from you” is the distance from you.
How to use
- Set your location and the date.
- Read what is up and when.
- Let your eyes dark-adapt for twenty minutes.
- Use a red light so you do not lose that adaptation.
Frequently asked questions
How do I tell a planet from a star?
Planets generally shine steadily while stars twinkle, because a star is effectively a point source and atmospheric turbulence disturbs it more. Planets also stay near the ecliptic, the line the Sun follows, so anything bright and steady near that line is worth a look.
Why does dark adaptation matter so much?
Because full adaptation takes twenty to thirty minutes and a single glance at a white phone screen resets much of it. This is why astronomers use red light — it preserves adaptation far better, and it is the single cheapest improvement to any observing session.
What can I see without a telescope?
A great deal. Five planets are visible to the naked eye, along with the Moon's major features through binoculars, several bright star clusters, the Andromeda galaxy from a dark site, and meteor showers. Binoculars you already own are a better first instrument than a cheap telescope.
How much does light pollution matter?
Enormously. From a city centre you may see a few dozen stars; from a genuinely dark site, thousands, along with the Milky Way. Driving out of town does more for observing than any equipment purchase, and it is why dark sky reserves exist.
What is the best time to observe?
After astronomical twilight ends and when the Moon is absent or low — a bright Moon washes out faint objects almost as effectively as light pollution. For planets, higher in the sky is better, since you are looking through less atmosphere.
Are the times exact?
They are computed for your coordinates, so they are accurate for a flat horizon. Hills, buildings and trees will delay a rise and hasten a set, sometimes by a great deal, and atmospheric conditions affect what is actually visible near the horizon.
🌐 This tool looks up results using the free Open-Meteo and Where-the-ISS-at APIs. The word you enter is sent to that service to fetch results; nothing is stored by this site.