Before the true distance of the Earth from the Sun was known,
and what the true distances in the Solar System were,
relative distances were measured by the Astronomical Unit.
It still is the most meaningful way to understand the scale of the Solar System
Astronomical Unit: The mean distance of the Earth from the
This distance is defined to be 1 A.U.
In 1772, the German astronomer Johann Bode found an empirical rule, dubbed Bode's Rule, that does a remarkable job of "predicting" planetary positions in the Solar System.
1. Write down a
sequence of 4s, one for each planet except Neptune, including one for
2. Add the sequence 0, 3, 6, 12, 24, ….
3. Divide these numbers by 10.
The result is the relative distance of each object from the Sun, to a surprising degree of accuracy!
What Is A Planet?
We all have heard that the Sun has nine planets circling around it, but what exactly is a planet?
e.g., Is Pluto a planet?
In the 1990s, many "asteroids" or "cometary nuclei" approaching 1/4
Pluto crosses Neptune's orbit, like an asteroid or a comet.
Pluto is only 1/2 the size of our own Moon. Seven planetary satellites are larger than Pluto.
Pluto has a highly inclined orbit.
Planet: A non-stellar body larger than a certain size (roughly 1,000 to 3,000 km), orbiting around a star as its primary host.
A List Of Important Numbers/Constants:
G = 6.67 × 10-11 N·m2/kg2
Astronomical Unit: 1 AU = 1.49 × 1011 m
Velocity Of Light: c = 3.00 × 106 m/s
Mass Of Sun: M¤ = 2.00 × 1030 kg
Radius Of Sun: R¤ = 6.96 × 108 m
Mass of Earth: MÅ = 5.98 × 1024 kg
Radius Of Earth: RÅ = 6.38 × 106 m
A Survey Of The Planets: Mercury
Notes: Very Small Magnetic
Field, Past Cratering,
Inter-Crater Plains - Past
A Survey Of The Planets: Venus
Notes: Thick Atmosphere,
Little/No Magnetic Field,
Evidence of Past/Present
A Survey Of The Planets: Earth
3475.6 Km (2159.7 miles)
Sidereal revolution period
Sinodic revolution period
Mean distance from Earth
384,400 Km (238,862 miles)
Minimum distance from
356,410 Km (221,469 miles)
Maximum distance from
406,697 Km (252,717 miles)
A Survey Of The Planets: Mars
Water In The Past,
A Survey Of The Planets: Jupiter
Solar System", Fast Rotation.
A Survey Of The Planets: Saturn
A Survey Of The Planets: Uranus
A Survey Of The Planets: Neptune
A Survey Of The Planets: Pluto
Small Size For Location, Highly
The Solar System: Minor Bodies
There is a lot of debris in the solar system, including meteoroids, asteroids and comets.
Asteroids: A small planetary body composed mostly of rock or metals; most orbit in the asteroid belt between Mars and Jupiter. All known asteroids have diameters less than 1,000 km. Lower size limit often taken to be about 10 m. Many unaltered since their formation - give clues to Solar System formation.
A small, extraterrestrial, solid body. Term usually used for
smaller than a
kilometer, and frequently millimeters, in size. Objects destined to become meteors.
Comets: An ice-rich planetesimal that can emit an observable gaseous halo when its ice is warmed by the Sun. Most comets spend their time in the outer Solar System, making it difficult to distinguish them from normal asteroids.
Comparison of Planet Properties