Live observing guide
Mercury never appears far from the Sun, so the useful observing window is short and close to the horizon.
BEYOND TONIGHT'S VIEW
Know this planet
- A year
- 88 days
- One orbit around the Sun · Earth days
- One rotation
- 58.65 days
- Relative to the stars, not sunrise to sunrise
- Diameter
- 4,879 km
- Measured across the equator
- Mass
- 3.3 × 1023 kg
- Total mass of the planet
- Mean temperature
- 167 °C
- Surface average; local temperatures vary
- Known moons
- 0
- Confirmed natural satellites
- Distance from Sun
- 57.9 million km
- Average distance along its orbit
- Gravity
- 3.7 m/s²
- Effective gravity at the equator
- Mean density
- 5,429 kg/m³
- Mass divided by volume
- Ring system
- No
- No known planetary rings
Rounded values. Moon counts checked on ; new discoveries can change the totals.
Catching the innermost planet and following its changing phase
- A bright star-like point low in twilight
- A tiny phase through a telescope
- Rapid position changes from one evening to the next
Observing tips
What you can really see
To the naked eye, Mercury is a small point in twilight, not a detailed globe.
A telescope may show its phase; low altitude often makes the image unsteady.
Before you leave
- Find a clear view of the indicated horizon before the short observing window.
- Use binoculars or a telescope only while the Sun is below the horizon. Never sweep near the Sun.
How to observe
- Check Mercury's direction and time here before going outside.
- Locate it with your eyes first, then centre it at low magnification.
- For a morning view, stop using optics before sunrise; do not keep tracking into daylight.