Originally Posted by vonBaur
WhoCares and Zamzow, you both forgot to take into account the rotation of our solar system near the outer limits of one arm of our galaxy, not to mention the likely motion of the galaxy itself trough space (although the last one might be difficult to calculate).
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Believe it or not, it wasn't forgotten but intentionally omitted. In fact, the topic triggered a bit of a deja-vu moment, as I looked up/discussed the topic of earth/solar system/galaxy speed earlier this year with some colleagues at work.
Based on that, I seriously considered to add the speed of the solar system (relative to galaxy center/SagA*, I guess).
The thing then gets indeed troublesome with the speed of the galaxy, as it is slightly more difficult to define a reference point relative to which to observe/calculate the speed. Back then I looked it up, and I seem to remember that they came up with a few "results", like the speed of the "local group" of galaxies (incl. the Mikyway) , but also others...