Titius-Bode Law - • Mercury 0.4 AU’s• Venus + 0.3 (0.7)• Earth + 0.6 (1.0)• Mars + 1.2 (1.6)• A. B. + 2.4 (2.8)• Jupiter + 4.8 (5.2)• Saturn + 9.6 (10.0)• Uranus +19.2(19.6) (Actually 19.2)• Neptune +38.4(38.8) (Actually 30)• Pluto is at 39.5

The Titius-Bode law works very well for the first six planets and the asteroid belt, but not very well for the planets after that. The Titius-Bode law is probably just a curious coincidence.

Mercury’s orbit is always within 0.5 AU of the Sun. It is always visually close to the Sun; therefore, it is only observed when low on the horizon (or during a solar eclipse).

It is visible for at most 2 hours on any given night.

Mercury was originally thought to be two planets. The Greeks called it Apollo when seen in the morning and Hermes when seen in the evening.

Mercury’s surface is fairly reflective.

Albedo - the fraction of incident sunlight an object reflects into space.

Mercury’s albedo is only about 0.1, similar to Earth’s Moon.

However, Mercury’s nearness to the Sun makes it one of the brightest objects in the night sky.

The best pictures of Mercury are taken by large telescopes during the day.

Mercury’s orbital period is 88 Earth days.

As viewed from the Earth, Mercury can pass over the surface of the Sun.

This is called a transit (a smaller, darker object passes across a larger, brighter one).

Transits of the Sun by Mercury are fairly rare. There are only twelve or so per century, always occurring in Nov. or May.

Radius - 2450 km0.38 Earth radii

Mass - 3.3 x 1026 g0.055 Earth’s

Density - 5.4 g/cm3

slightly less than Earth’s

Mercury is now the smallest planet. (It is larger than Pluto, so it was second smallest before Pluto’s demotion to dwarf planet.)

Mercury’s rotational period is 59 days, which is 2/3 of a Mercury year.

Mercury goes through three rotations for every two revolutions.

There is a reason for this 2/3 ratio. Part of the reason is Mercury’s very eccentric orbit (very elliptic).

This causes the orbital speed to vary greatly throughout the orbit.

The orbital and rotational periods are synchronous at perihelion (closest approach to the Sun).

How would this appear from Mercury?

The Sun would move from east to west, except near perihelion, where rotation is slightly slower than orbital speed.

At this time the Sun would appear to stop and go backward before it resumed its east to west motion.

Mercury’s equator is exactly in the orbital plane, so Mercury has no axial tilt.