The thing is Mercury's orbit is tipped with respect to Earth's and crosses the plane of our orbit at only two points. For a transit to occur, Mercury must lie near one of those points when it passes us. To meet these conditions, Mercury must slip between Earth and the Sun within 3 days of May 8 or within 5 days of November 10.
The unequal size of these "transit zones" reflects the eccentricity of Mercury's orbit, which gives us twice as many transits in November as in May. Mercury lies farther from the Sun and moves much slower in May, which reduces our chance of catching it in the right place. But Mercury's disk appears 20-percent larger during May transits because it's closer to us then.
Surjodeb Basu (/dev)
No comments:
Post a Comment