Mercury
Mercury completes an orbit around the Sun in roughly three months. Because it stays close to the Sun in the sky and never reaches more than about 25° of separation, it is usually seen only in bright twilight. That makes Mercury difficult to observe, even though it can shine about as brightly as Sirius.
Like the Moon, Mercury shows phases as it moves around the Sun. In a telescope these changing phases can be seen during the short windows when the planet is far enough from the Sun's glare to observe.
A complete observing sequence runs from superior conjunction, when Mercury lies near the Sun's direction but beyond it, through greatest elongation, and onward to inferior conjunction, when Mercury passes between Earth and the Sun.
- Physical Data
- Mercury
- Mass ratio Sun/planet
- 6'023'600
- Mass of planet
- 0.330220 1024 kg
- Equator radius
- 2439.7 km
- Rotation period
- 58.6462 days
- Flattening
- 0
- Density
- 5.43 kg/dm3
- Visual magnitude at 1 AU
- -0.42 mag
- Albedo
- 0.106
- Northpole RA
- 11h42.5m
- Northpole DE
- 61.44°
- Orbit Data
- Mercury
- Revolution period
- 87 days 23 hours
- Sun radiation power
- 6170-14'300 W/m2
- Distance from Sun (min)
- 46 Mio km
- Distance from Sun (max)
- 70 Mio km
- Distance from Earth (min)
- 80 Mio km
- Distance from Earth (max)
- 220 Mio km
- Orbital Elements*
- Mercury
- Inclination
- 7.00534°
- Longitude of node
- 48.3382°
- Longitude of perihel
- 77.4453°
- Semi-major axis
- 0.3870999 AU
- Daily motion
- 4.092319°/day
- Eccentricity
- 0.2056241
*) Epoche 8 January 1994, 0h UT, Equ. J2000