Astronomy Ephemeris Calculator: Explore the Solar System Through Time
Planets are constantly changing position, distance, apparent size and brightness. An ephemeris tells us how those properties change with time.
Four ways to follow a Solar System object
21 September 2026
Compare the brightness, distance, apparent size and sky position of Solar System objects on any date.
| Object | Magnitude | Distance | Apparent size | RA | Dec |
|---|---|---|---|---|---|
| Sun | -26.73 | 1.004370 AU | 1,911.37″ | 11h 51m 27.0s | — |
| Moon | -10.80 | 0.002689 AU | 1,782.75″ | 19h 32m 55.3s | −24° 59′ 55.0″ |
| Mercury | -0.30 | 1.287470 AU | 5.23″ | 12h 58m 37.9s | −06° 48′ 03.3″ |
| Venus | -4.80 | 0.409432 AU | 40.79″ | 14h 04m 08.0s | −18° 57′ 04.0″ |
| Mars | 1.11 | 1.729560 AU | 5.41″ | 07h 50m 05.1s | +21° 53′ 26.5″ |
| Jupiter | -1.84 | 5.900060 AU | 32.70″ | 09h 19m 57.9s | +16° 10′ 25.0″ |
| Saturn | 0.39 | 8.181970 AU | 19.64″ | 00h 48m 14.2s | +02° 14′ 33.1″ |
| Uranus | 5.67 | 18.904200 AU | 3.70″ | 04h 13m 30.8s | +21° 01′ 34.3″ |
| Neptune | 7.68 | 28.734200 AU | 2.36″ | 00h 12m 22.7s | — |
| Ceres | 8.96 | 2.713440 AU | 0.48″ | 06h 56m 10.0s | +23° 04′ 42.2″ |
| Vesta | 6.71 | 1.385560 AU | 0.52″ | 01h 48m 50.0s | −01° 07′ 40.5″ |
| Pluto | 14.53 | 34.844100 AU | 0.09″ | 20h 24m 46.4s | −23° 42′ 10.1″ |
Values are read from the JPL-derived ephemeris data used throughout Show Me The Sky.
Choose an object and explore
How does it change?
Venus — Magnitude
What do these parameters tell us?
Brightness and apparent size
A planet's appearance changes as both its distance and geometry relative to Earth and the Sun change.
The magnitude scale describes apparent brightness, while angular size describes how large an object appears in the sky.
Distance and elongation
One astronomical unit (AU) is approximately the mean Earth–Sun distance.
Elongation measures the apparent angular separation between an object and the Sun. It is especially useful when considering the visibility of Mercury and Venus.
The Solar System is a moving system
A planet does not have one fixed distance, apparent diameter or brightness. Those quantities continually change as Earth and the other planets move around the Sun.
Ephemerides turn that orbital motion into predictions we can use to plan observations and understand what we see through a telescope.
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