Measuring Orbit About Galactic Center
How do scientists find out how fast our solar system goes
around the Milky Way Galaxy?
A very good question. It is a complex process. First it is
necessary to observe and calculate the rates of rotation of galaxies
that we think are the size of ours. We learn that they all rotate
around their centers in about 225 million years. If ours does the
same thing, and our solar system is part of it, then it rushes around
the galactic center about every 225 million years.
For a fourth or fifth grader, actually for anyone, that is a
profound question. I am very proud of you for asking it. To learn
the rotation, and measure it, astronomers have mapped large star forming
regions in our galaxy using big radio telescopes like the VLBA (Very
Large Baseline Array) radio telescope. The astronomers can determine
the shift of these masses of star forming regions in three dimensions
over time. By the way, the last time we were here in our orbit
about the galaxy, dinosaurs were
just beginning to appear at the start of the Triassic.
David H. Levy
Imagine you are in a car and the speedometer of the car is not
working. How would you measure how fast you were going? If you knew
the distance between light poles or electrical poles, then you might
try to measure the time it takes for the car to get from one pole to
another. Or, if you happen to be driving through one of those
beltways (like the 275 around Cincinnati or the 465 around
Indianapolis) then you could measure the time it takes to start from
one landmark, go around once and get to the same landmark.
It is the same with measuring how fast the Milky Way Galaxy rotates,
and how fast we are moving. We are always measuring our speed versus
some fixed point. In the case of the solar system, we have to choose
a fixed point that is not part of the Milky Way Galaxy, is far
enough away from us so that it essentially unaffected by the local
motion of the galaxies around us. So, for our fixed point, we might
choose a bunch of distant galaxies and measure how fast we move
relative to them. We would have to make some adjustments in
calculations because the galaxies are moving relative to each other,
and the distances and changes are harder to measure, but that would
simply be like, as in our example above, measuring the speed of a
car, based on a fixed point like the Sun. It is not as easy as
measuring from light poles, but it can still be done.
Greg (Roberto Gregorius)
Here is a cool article on the Internet that discusses the speed of the solar
system in the milky way.
How do scientists measure this?
just like a ship entering a port, the ship's position is at the intersection
of lines of bearing from known points. The same applies to our celestial
environment. By mapping earth's position relative to stars, the earth's
position can be determined from time-to-time and the earth's movement can be
measured over time as its position changes.
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Update: June 2012