Our Planets – Pics of Sizes, Orbits, Location in the Milky Way, etc.

I. Relative size of planets

The Sun and the gas giant planets like Jupiter are by far the largest objects in the Solar System. The other planets are small specks on this scale, as the following figures illustrates. (Images taken from http://www.kiroastro.com/writings/perspective)

Relative size of Terrestrial planets (and Pluto)

 

Relative size of all planets

 

Relative size of Sun and planets

 Our Sun is a fairly typical star. But it is quite a minnow compared to other stars. Take a look at the next two images.

Relative size of Sun and other (big) stars

 

II. Mass and densities

The total mass of all planets are also concentrated in the Gas Giant planets Jupiter, Saturn, Uranus, and Neptune, as the following graph indicates. In fact, Jupiter, by itself, has more mass than all the other planets combined! (Pictures below are from: http://csep10.phys.utk.edu/astr161/lect/index.html).

 

III. Planetary orbits

The average separation of the planets from the Sun (in astronomical units)

Here is the entire Solar System to scale for the orbits. Position of planets is for Fall, 1996:

Notice the enormous amount of empty space in the outer Solar System. To show the entire Solar System to scale, the inner Solar System becomes so compressed that the planet orbits almost appear to run together. The very large eccentricity of Pluto’s orbit is also obvious.  Pictures from: http://csep10.phys.utk.edu/astr161/lect/index.html

The planetary orbital planes are inclined at small angles to the ecliptic:

Note: Pluto’s orbit is highly tilted (17 degrees) relative to the plane of the ecliptic. .  Picture from: http://csep10.phys.utk.edu/astr161/lect/index.html

Side view of the inner Solar System, Fall, 1996

In this figure the white portion of the orbit is above the ecliptic plane and the yellow portion is below. Notice that the orbits of the inner planets are nearly, but not quite, in the same plane. The orbit of Mercury, in addition to being the most eccentric, has the largest tilt (7 degrees) with respect to the ecliptic plane. .  Picture from: http://csep10.phys.utk.edu/astr161/lect/index.html

III. Obliquity

Most of the planets rotate about their rotation axis in the same sense, which is prograde. Venus rotates in the opposite, retrograde sense:

 

 

Summary of Observations in the Solar System

  • Planetary orbits all nearly in the ‘ecliptic’ plane (except for Pluto)
  • Planets all revolve in the same direction around the sun
  • Most planets have ‘prograde’ rotation (except for Venus – weakly retrograde & Uranus – on its side)
  • Two types of planets dependent on distance from sun
      1. Close – Terrestrial, small & high density
      2. Far – Great, big and low density
  • Each planet roughly twice as far as its neighbor (Bode’s law)
  • Sun has 99.9% of mass
  • Planets have 99% of angular momentum

A lot more information (and better pictures) can be found in many places on the web, for instance on the Solar System site on Wikipedia.

 

Where we are in the Milky Way

There is more stability in the galactic environment the further out one goes from the center of a galaxy.  Closer to the center there is more density of “stuff” and more activity of space matter flying around and colliding which probably makes life more difficult to evolve.

 

Originally Posted at:  http://www.ualberta.ca/~dumberry/geoph110/earth_planets.htm

……with some alterations

 

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