Your guide to Celest
More help, less jargon
Choose how much detail you want, understand unfamiliar terms, and learn how every recommendation is produced.
See which condition helps or hurts your view, in plain language.
Open the sky glossaryLearn the unfamiliar words exactly when you need them.
Plan your first observationFind an easy event, check what to bring, and add it to your calendar.
Made for curious people
Simple by default.
Detailed when you ask.
We translate astronomical calculations into plain language first, while keeping the real numbers one tap away.
Saturn is visible tonight
Look southeast after 11:40 PM. Saturn will appear as a steady, pale-gold point above the horizon.
No telescope needed to find it.Start with the essentials
The night sky, in plain language.
Twilighti
The period after sunset or before sunrise when the Sun is below the horizon but the sky is not fully dark.
Why it mattersFaint stars become easier to see as twilight progresses from civil to nautical and then astronomical.
Astronomical nighti
The darkest part of the night, when the Sun is at least 18° below the horizon.
Why it mattersThis is usually the best time for galaxies, nebulae, faint meteors, and the Milky Way.
Golden houri
The warm, soft-light period close to sunrise or sunset. It is beautiful for photography, but the sky is too bright for stargazing.
Why it mattersIt helps photographers plan, while stargazers know they still need to wait for darkness.
Light pollutioni
Artificial light from streets, buildings, and cities that makes the night sky brighter.
Why it mattersMore light pollution means fewer stars and much less detail in galaxies, nebulae, and the Milky Way.
Bortle classi
A scale from 1 to 9 describing how dark the sky is. Class 1 is extremely dark; class 9 is a bright inner-city sky.
Why it mattersIt gives you a realistic limit for what can be seen even when the weather is perfect.
Magnitudei
A brightness scale used for stars and planets. Lower and negative numbers mean a brighter object.
Why it mattersA planet at magnitude −2 is much easier to see than an object at magnitude +6.
Moonlight impacti
The amount of natural sky glow created by the Moon during your observing time.
Why it mattersA bright Moon can hide faint stars even when there are no clouds and you are far from a city.
Planetary oppositioni
The moment when a planet appears opposite the Sun in our sky.
Why it mattersThe planet is often near its brightest, rises around sunset, and remains visible for most of the night.