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
15 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 | 1.006040 AU | 1,908.21″ | 11h 29m 56.0s | +03° 14′ 44.7″ |
| Moon | -7.96 | 0.002637 AU | 1,818.18″ | 14h 18m 45.7s | −19° 02′ 50.3″ |
| Mercury | -0.50 | 1.335140 AU | 5.04″ | 12h 25m 13.4s | −02° 27′ 42.9″ |
| Venus | -4.76 | 0.450764 AU | 37.05″ | 13h 53m 39.5s | −17° 13′ 01.9″ |
| Mars | 1.16 | 1.767030 AU | 5.29″ | 07h 34m 31.4s | +22° 25′ 13.4″ |
| Jupiter | -1.83 | 5.956170 AU | 32.39″ | 09h 15m 17.8s | +16° 30′ 49.7″ |
| Saturn | 0.42 | 8.210880 AU | 19.57″ | 00h 49m 49.9s | +02° 25′ 22.6″ |
| Uranus | 5.68 | 18.999800 AU | 3.68″ | 04h 13m 40.2s | +21° 01′ 57.7″ |
| Neptune | 7.68 | 28.747000 AU | 2.36″ | 00h 12m 58.7s | — |
| Ceres | 9.01 | 2.792530 AU | 0.47″ | 06h 48m 11.5s | +22° 59′ 57.8″ |
| Vesta | 6.82 | 1.413990 AU | 0.51″ | 01h 52m 14.0s | — |
| Pluto | 14.52 | 34.759100 AU | 0.09″ | 20h 25m 05.2s | −23° 41′ 13.6″ |
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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