What is in the sky tonight, and the numbers behind it
You do not need a telescope to enjoy the night sky, just a little information about what is up there and when. These free astronomy tools give you that for any place and date. The moon phase calculator shows tonight’s phase, illumination and the next new and full moons; the moonrise and moonset calculator gives the times for your location; planets visible tonight lists which planets are above the horizon, where to look and how bright they are; and the star chart draws the sky over your head with constellations labelled, so you can match it to what you see.
For events, the ISS pass predictor tells you when the International Space Station will cross your sky and how bright it will appear, the meteor shower calendar lists the year’s showers with peak nights and expected rates, and the solar eclipse countdown counts down to the next eclipse and shows where it will be visible. The sun position calculator gives sunrise, sunset, solar noon and the sun’s altitude and direction at any hour, which photographers and solar panel installers use as much as stargazers do.
The calculations run in your browser using standard astronomical algorithms, so your location is never sent anywhere; you can type a city, enter coordinates or let the browser read your position. Results are good to within a minute or so for rise and set times, and the pages explain what each number means, which makes them a fair companion for school projects, outreach nights and planning a photo of the Milky Way.
Converters and calculators for astronomy
- Distances. The light-year converter switches between light-years, parsecs, astronomical units and kilometres, and shows how long light takes to cross the distance.
- Time. The Julian date converter turns a calendar date and time into the Julian Day used in observation logs and back again, and the sidereal time calculator gives local sidereal time for your longitude, the number you need to point a telescope by right ascension.
- Fun with gravity. Weight on other planets shows what you would weigh on the Moon, Mars, Jupiter and the rest, and age on other planets converts your age into years on each world, with your next “birthday” on Mercury or Mars.
Tips for a better night out
- Check the moon first. A bright moon washes out meteors and faint stars, so plan showers and deep-sky viewing for nights near the new moon.
- ISS passes are brightest when the station is lit by the sun while your sky is dark, usually within two hours of sunset or sunrise. The predictor lists only passes that reach a useful height above the horizon.
- Give your eyes 20 minutes to adapt to the dark, and use the star chart in its red night mode so the screen does not undo that.
- Planet positions are the same from anywhere in the world on a given night, but rise and set times are not, so always set your location before reading them.
- Never look at the sun without proper eclipse glasses or a solar filter, even during a partial eclipse. The countdown page links to safe viewing advice.
Space & Astronomy: frequently asked questions
How accurate are the moon and sun times?
Rise, set and phase times come from the same published algorithms used in almanacs and are usually within a minute of official tables. Local horizon, altitude and atmospheric refraction can shift what you actually see by a minute or two.
Do the tools need my location?
The star chart, rise and set times, ISS passes and sun position depend on where you are. You can type a place name or coordinates instead of sharing your position, and whatever you enter stays in your browser.
Why is the ISS visible some nights and not others?
The station is only visible when it is above your horizon, lit by the sun and your sky is dark. Its orbit shifts each day, so there are runs of visible evenings or mornings followed by weeks with none.
Can I use the star chart on my phone outdoors?
Yes. The chart works on a phone browser, has a red night-vision mode and can be oriented to the direction you are facing. It does not require an app or an account.
What is a Julian date and who uses it?
The Julian Day is a continuous count of days since 4713 BC used by astronomers to timestamp observations without worrying about calendars, months or time zones. Variable star observers, satellite trackers and software all use it.