by Anthony Barreiro » Thu May 16, 2013 5:07 pm
APOD Robot wrote: Swinging around the Sun's eastern limb on Monday, ...
I always get confused when I read "east" and "west" referring to the surfaces of solar system bodies. Objects on the surface of the Sun rotate from east to west in Earth's sky, but if we were wearing asbestos underwear and floating next to a sunspot on the surface of the Sun's photosphere, we would be moving from west to east.
The same with the Moon. Mare Crisium is on the western edge of the Moon's visible face in Earth's sky, but if we were astronauts at the Apollo 11 landing site in Mare Tranquilitatis, Mare Crisium would be toward the east on the surface of the Moon. The Sun rises on Mare Crisium before it rises on Mare Tranquilitatis, just as it rises on New York before rising on San Francisco.
Jupiter's Great Red Spot rotates from east to west in Earth's sky, but from west to east on the surface of Jupiter's cloud tops.
The terms "preceding" (west in Earth's sky, east on the surface of a solar system body) and "following" (east in Earth's sky, west on the surface of a solar system body) seem to have fallen out of favor, but they are clearer than using east and west. In this case, we would say that this sunspot is rotating around the Sun's following limb.
[quote="APOD Robot"] Swinging around the Sun's eastern limb on Monday, ... [/quote]
I always get confused when I read "east" and "west" referring to the surfaces of solar system bodies. Objects on the surface of the Sun rotate from east to west in Earth's sky, but if we were wearing asbestos underwear and floating next to a sunspot on the surface of the Sun's photosphere, we would be moving from west to east.
The same with the Moon. Mare Crisium is on the western edge of the Moon's visible face in Earth's sky, but if we were astronauts at the Apollo 11 landing site in Mare Tranquilitatis, Mare Crisium would be toward the east on the surface of the Moon. The Sun rises on Mare Crisium before it rises on Mare Tranquilitatis, just as it rises on New York before rising on San Francisco.
Jupiter's Great Red Spot rotates from east to west in Earth's sky, but from west to east on the surface of Jupiter's cloud tops.
The terms "preceding" (west in Earth's sky, east on the surface of a solar system body) and "following" (east in Earth's sky, west on the surface of a solar system body) seem to have fallen out of favor, but they are clearer than using east and west. In this case, we would say that this sunspot is rotating around the Sun's following limb.