planet
Mercury
Locked in a 3:2 spin-orbit resonance, turning exactly three times on its axis for every two trips around the Sun. Its iron core fills about 85% of the planet radius, which is why so little is left over for rock.
Position
Computed on . For a continuously updating figure, open the live simulation.
When to look
Mercury never strays far from the Sun, so it is only visible near dawn or dusk. It is best placed at greatest elongation, when its angular separation from the Sun peaks.
| Date (UTC) | Event | Separation | Distance from Earth |
|---|---|---|---|
| greatest evening elongation | 25.2° | 1.00 AU | |
| greatest morning elongation | 19.6° | 1.00 AU | |
| greatest evening elongation | 18.3° | 0.96 AU | |
| greatest morning elongation | 27.6° | 0.92 AU |
About Mercury
Mercury never strays far from the Sun in our sky, which is why it is the naked-eye planet most people have never knowingly seen. Its 3:2 spin-orbit resonance produces a solar day of 176 Earth days — two full years — so a given point on the surface bakes for months and then freezes for months. Despite being the closest planet to the Sun it is not the hottest; Venus takes that with its atmosphere.
Physical data
- Diameter
- 4,879 km
- Mass
- 0.055 earths
- Surface gravity
- 3.70 m/s2
- Rotation
- 58.65 d
- Solar day
- 176 d
- Year
- 88.0 d
- Axial tilt
- 0.03 deg
- Mean temperature
- 167 C
- Moons
- none
Positions from VSOP87, accurate to within one arcminute. Physical constants are published values and are not computed here.