AboutJames Gort Expertise Questions on observational astronomy, optics, and astrophysics. Specializing in the evolution of stars, variable stars, supernovae, neuton stars/pulsars, black holes, quasars, and cosmology.
Experience I was a professional astronomer (University of Texas, McDonald Observatory), lecturer at the Adler Planetarium, professor of astrophysics, and amateur astronomer for 42 years. I have made numerous telescopes, and I am currently building one of the largest private observatories in Canada.
Publications StarDate, University of Texas, numerous Journal Publications
Question I have been reading through the questions and this seems to pop up quiet a bit. The question I have is not "how" but "how do we know its tilting at 7.25 degrees, when actually the sun could be positioned at 0 degrees and it is infact us that is tilting that 7.25 degrees. How can they say the sun is tilting when there is no ground in space to stand on. How do they know which way is up/down?
Thanks
Answer Hello Matt,
You are correct that there's no absolute frame of reference. However, in our solar system, the plane of the earth's orbit was chosen (arbitrarily) to be the "zero" reference, and other orbits and revolutions are measured relative to it. So 7.25 degrees refers only to its rotation relative to earth's orbital plane.
