The Solar System is located in the grouping of stars (galaxy) known as
the Milky Way galaxy. The Milky Way is just one of many billions of
galaxies in the Universe. The Milky Way galaxy is a spiral
galaxy which contains roughly 100 billion stars and has a mass of roughly
10 - 100 billion M. The
visible material of the Milky Way is
contained in a thin rotating disk. The diameter of the disk is on
the order 100,000 - 300,000 light years (1 light year = 6 trillion
miles = 9.3 trillion kilometers)
and has a thickness of several thousands of light years. The
disk of the Milky Way is very thin.
The appearance of the Milky Way is quite striking (probably). In the center of the disk is a bulge out of which extends several spiral arms. The Solar System is located in one of the arms roughly two-thirds of the way out from the center of the disk. The Solar System orbits the center of our Galaxy with a speed of roughly 220 kilometers per second or 800,000 kilometers per hour!
Can you estimate the mass of our Galaxy?
Comment -- The Milky Way galaxy has another componet (in addition to the visible disk). There is a large spherical component to the Milky Way which is made up of nonluminous material ( Dark Matter). The Milky Way is dominated by this Dark Matter component. Perhaps 90 % of the Milky Way is nonluminous. This is also true for the Universe where as much as 99 % of the Universe may be nonluminous!!
The average mass of a star in the Milky Way galaxy is 0.3
M. The Sun is
slightly larger than average, but it is not
really that far out of line. It seems to be just 1 out of the hundred
billion stars which make up the Galaxy. It is not atypical. Given
such facts, it is not unreasonable to suspect that the Solar System is
not unique. We will return to this issue at various times in the future.
The Solar System displays a seemingly incomprehensible amount of diversity. However, on a closer look, we see many regularities and patterns in the Solar System. It is these regularities and patterns which hold the key to our understanding of the mechanics of the formation of the Solar System.
The above general properties of the motions of the planets are quite significant. There are also some vexing properties which people also need to explain, e.g.,
Planetary Properties. I
For a little bit of scale:
Mass of the Earth = 5.9742x10**24 kilograms
Mass of the Sun = 1.99x10**30 kilograms = 328,900 M
Diameter of the Earth = 12,756 kilometers
Diameter of the Sun = 1,392,000 kilometers = 109 D
So, adding up the masses of the planets (and including the asteroids
which are < 0.001 M), we see that the Sun is > 99 % of the
mass of the Solar System.
Random Comments
The regularities of the planets are clearly tied to how far they are away from the Sun. The Terrestrial planets are closer to the Sun than are the Jovian planets. In general, the Terrestrial planets are smaller and more dense than the Jovian planets. Let's concentrate on the density for a second (as this is an important point).
There is a clear distinction between the Terrestrials, Jovians, and Icy Planets in terms of their
Comments--