Some Facts:
- 36 million miles / 58 million km from Sun
- orbits Sun in 88 days
- rotates on axis in 59 days
- 3,000 miles in diameter - less than half that of Earth
(about 3/4 the size of Mars or 1.5 times the size of the Moon)
- Mercury's orbit has more "tilt" than most of the planets.
Because of this, "transits" when Mercury appears to travel across
the face of the sun are rare, occurring only every few decades. The last transit
was in 2003.
- Exploratory missions: Mariner 10 (3 passes: 3/29/74; 9/21/74; 3/16/75)
- no atmosphere
Observing Notes
- Mercury is never more then 28 degrees from the Sun, so we can only see it
in twilight, never in dark sky.
- Best evening views for us occur in spring shortly after sunset. The ecliptic
is at its highest and Mercury is at its "greatest eastern elongation"
- its greatest separation from the sun from our point of view.
(The other best time to observe it is in the fall before sunrise - when it
is at "greatest western elongation.")
- Mercury is very bright in a telescope (it's close to the sun & has a
reflective surface)
- Mercury shows phases like the Moon and Venus. At the "greatest elongation"
viewing times, it is a half-disk. However, it's hard to get a good view of
the shape because we are looking through so much atmosphere, and air movement
makes the image ripply or blurry. A colored filter may help show the half-disk,
or at least an oblong shape.
Filters:
(from the information provided with Celestron filter packages)
- Orange (#21, 46% T): during daylight observing reduces the brightness
of the blue sky to enhance surface features
- Light Red (#23a, 25% T): Improves observation at twilight when the
planet is low near the horizon and in daylight it reduces the brightness of
the blue sky to enhance surface features.
- Red (#25, 14% T): Improves observation at twilight when the planet
is low near the horizon and in daylight it reduces the brightness of the blue
sky to enhance surface features.
- Violet (#47, 3% T): helpful in detecting faint features.
- Light Blue (#80a, 30% T): Improves observation of dusky surface markings
at twilight when the planet is low near the horizon.
Mythology:
The planet was associated with quickness (think of the term "mercurial")
because it appears to move rapidly, changing position noticeably over just a
few days.
Nabu: In Mesopotamia, the planet represented the god Nabu, son of the
king god Marduk. Nabu was the scribe of teh gods and the patron god of scribes.
He was an important character in the spring New Year festival, rescuing Marduk
from captivity and restoring order for the coming year, then recording the judgments
of the gods as they decided the destiny of the world for the coming year. Nabu
was also a rainmaker.
Hermes: The Greek god Hermes was originally a god of fertility and
travellers. He was also a clever trickster god, guided the dead to the underworld,
and served as the gods' messenger and Zeus' cupbearer.
Mercury is the Roman equivalent of the Greek god Hermes.
Sources:
Cornelius, Geoffrey and Paul Devereux, The Secret Language
of the Stars and Planets, Chronicle Books, 1996.
Windows to the Universe website.
photo from NASA website
