CoachA solar eclipse happens when the Moon passes exactly between Sun and Earth, and its shadow falls on us. Where the Moon’s umbra touches the Earth — a racing spot rarely two hundred kilometres wide — the Sun’s disc is entirely hidden: total eclipse, night at noon, stars out. In the vast surrounding penumbra, the Sun is only partly bitten: partial eclipse.
Examples
Example 50.6 (Why so rare?)
New moon comes every month — why not a solar eclipse every month? Because the Moon’s orbit is tilted, by about five degrees, against the Earth’s path around the Sun. Most months, the new moon passes above or below the Sun–Earth line, and its shadow spears harmlessly into space. Only when a new moon happens just as the Moon crosses the alignment plane do the three worlds line up — a few times a year somewhere on Earth, and for any particular town, totality is a once-in-lifetimes visitor.