Mercury
What is Mercury?
Planets· Diameter 4,879 km. The innermost planet, with a 600 °C swing between day and night. BepiColombo arrives in orbit in November 2026 after a seven-year cruise.
📍 Visible from where you are right now — computed in your browser
bearing · altitude · rise time · best time tonight
Where Mercury is in your sky right now: https://nowsky.org/solar/sky?sel=mercury — location and time set automatically, no login.
Orbit and size
| Diameter | 4,879 km |
|---|---|
| Distance | 0.39 AU |
| Year | 88 d |
| Temp | -173~427 °C |
Figures are representative approximations. Source: compiled from NASA and IAU public data.
Related events
- BepiColombo launch — to Mercury
- BepiColombo enters Mercury orbit(planned)
- Transit of Mercury (2032)(planned)
Frequently asked
- How big is Mercury?
- 4,879 km.
- How far is Mercury from Earth?
- 0.39 AU.
- In one line, what is Mercury?
- Planets — The innermost planet, with a 600 °C swing between day and night.
- Where is Mercury in the sky right now?
- Open the sky view for your location and time and it shows the position in the sky right now.
When the Sun stops and backs up in Mercury's sky
Near perihelion Mercury's orbital motion briefly outpaces its rotation. For a few days an observer on the surface would see the Sun stop in the sky, slide back toward the east, then resume its westward course. Nothing like it happens on Earth; it follows from Mercury's orbital eccentricity of 0.21, among the largest of the planets.
The longitudes where this retrograde loop is visible are fixed, so certain places on Mercury get a morning with two sunrises. The Sun there appears two and a half times wider than from Earth, and with no atmosphere the daytime sky stays black. The sky view shows Mercury as seen from Earth, but following Mercury in the orbit view and slowing the replay through perihelion reveals the days when the orbit overtakes the spin.
The planet in depth
Mercury is the closest planet to the Sun but not the hottest (that's Venus). With no atmosphere to hold heat, it swings from 430 °C by day to −180 °C at night — the most extreme range in the solar system. Its clock is stranger still: rotation and orbit lock 3:2, so one Mercurian day, sunrise to sunrise, lasts two Mercurian years.
The surface is Moon-like cratered plains, but the interior is not: Mercury is the second-densest planet, with a core spanning 85% of its diameter — a planet seemingly stripped of its mantle, probably by a giant impact. BepiColombo is arriving to dig into that mystery.
And in the permanent shadows of its polar craters, there is genuine water ice — 58 million km from the Sun. Such is the power of shade.
Mercury's day is strange arithmetic: a 59-day spin locked 3:2 with an 88-day orbit means sunrise to sunrise takes 176 days — Mercury's 'day' is twice its 'year.' Near perihelion the orbit briefly outruns the spin, and the Sun stalls in the sky and slides backward. And in permanently shadowed polar craters, the innermost planet keeps a confirmed stash of ice.
Related
Figures are representative approximations. Simulated positions use J2000 mean elements.