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Name: JK
Status: other
Grade: other
Location: NV
Country: N/A
Date: N/A

How do scientists find out how fast our solar system goes around the Milky Way Galaxy?

Dear JK,

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)
Canisius College


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.

Sincere regards,

Mike Stewart

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