What is the speed of the Solar System?
(by Amara Graps)
Or, how fast is the Sun (Solar System) hurling towards
the constellation Hercules?
From the book: _Guide to the Galaxy_, 1994; Henbest and Couper;
Cambridge University Press.
The Sun is moving towards Lambda Herculis at 20 kilometers per second
or 12 miles per second. Or in units "per hour": 72,000 kilometers per
hour or 45,000 miles per hour. This speed is in a frame of rest
if the other stars were all standing still.
The three-dimensional picture of the Sun's movement through the Galaxy
is a little more complicated.
The Sun is moving upwards, out of the plane of the Milky Way, at a
speed of 7 kilometers per second. Currently the Sun lies 50
light-years above the mid-plane of the galaxy, and its motion is
steadily carrying it further away.
But the gravitational pull of the stars in the Galactic (Milky Way)
plane is slowing down the Sun's escape. The astronomer Frank Bash
estimates that in 14 million years the sun will reach its maximum
height above the Galactic disk. From that 250 light-year position, it
will be pulled back towards the plane of the Galaxy. Passing through,
it will travel to a point 250 light-years below the disk, then
oscillate upwards again to reach its present position 66 million years
from now. We crossed the plane 2 million years ago. We are currently
in the thick of the galactic disk and our view of distant regions is
largely blocked by dust but 10-20 million years from now, our motion
will allow a full view of our starry galaxy.
The Sun-Galactic center distance is 25,000 light-years -- plus or minus
2,000 light-years. The galaxy is thought to be 100,000 light-years in
diameter and we are thought to be about halfway out from the center
(used to be thought that we were two-thirds out).
If you have a good idea of the Sun's distance from the Galactic
center, then the solar system's speed can be approximated. Using
speed measurements of the gas at different distances from the Galactic
center, the Sun appears to be cruising along at 200 kilometers per
second and it takes 240 million years to complete the grand circuit
around the Galaxy. This speed is an absolute speed.
Note:
1 light-year = 9.46*10^{15} meters
1 parsec = 3.08*10^{16} meters
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Special Thanks to A. Graps