Titius-Bode Law -

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Titius-Bode Law -

• Mercury 0.4 AUs
• 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

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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.
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Mercurys 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).
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It is visible for at most 2 hours on any given
night.
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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.
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Mercurys surface is fairly reflective. Albedo
- the fraction of incident sunlight an object
reflects into space.
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Mercurys albedo is only about 0.1, similar to
Earths Moon.However, Mercurys nearness to the
Sun makes it one of the brightest objects in the
night sky.
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The best pictures of Mercury are taken by large
telescopes during the day.
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Mercurys orbital period is 88 Earth days.As
viewed from the Earth, Mercury can pass over the
surface of the Sun.
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This is called a transit (a smaller, darker
object passes across a larger, brighter one).
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Transits of the Sun by Mercury are fairly rare.
There are only twelve or so per century, always
occurring in Nov. or May.
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Radius - 2450 km 0.38 Earth radiiMass - 3.3
x 1026 g 0.055 EarthsDensity - 5.4
g/cm3 slightly less than Earths
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Mercury is now the smallest planet. (It is
larger than Pluto, so it was second smallest
before Plutos demotion to dwarf planet.)
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Mercurys rotational period is 59 days, which is
2/3 of a Mercury year.
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Mercury goes through three rotations for every
two revolutions.
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There is a reason for this 2/3 ratio. Part of
the reason is Mercurys very eccentric orbit
(very elliptic).
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This causes the orbital speed to vary greatly
throughout the orbit.
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The orbital and rotational periods are
synchronous at perihelion (closest approach to
the Sun).
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How would this appear from Mercury?
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The Sun would move from east to west, except near
perihelion, where rotation is slightly slower
than orbital speed.
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At this time the Sun would appear to stop and go
backward before it resumed its east to west
motion.
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Mercurys equator is exactly in the orbital
plane, so Mercury has no axial tilt.
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