The comet landing by Philae/Rosetta today is tremendously exciting! But it
did get me wondering what reference frame is being used to measure the
comet's speed. News reports quote a comet speed of over 40,000 mph. What
reference frame is this speed measured in? If a frame centered in the
earth, wouldn't the comet's speed become a function of where the earth is in
its orbit (i.e. heading away or towards the comet) as well as where the
earth is in its daily rotational cycle (i.e. turning toward or away from the
comet? What reference frame is normally used when quoting speeds of solar
system objects and space probes?
Don
Dr. Donald Polvani
Adjunct Faculty Physics (Retired)
Anne Arundel Community College
Arnold MD 21012