Whenever the Sun is within 18.5° of a node.
The Sun travels along the ecliptic at about 1° per day
It takes about 37 days to cross through the eclipse zone centered on each node.
A New Moon occurs every 29.5 days and therefore at least one solar eclipse must occur during each of the Sun's node crossings.
“Saros” : Greek meaning “Repetition”
1 Saros = 18 years, 11 1/3 days
Line of nodes drifts westward at 19 deg / year
Eclipses repeat because the moon and the nodes return to the same place wrt the sun
The 1/3 day means you must go through 3 Saros to have an eclipse at the same location on the Earth (54 years, 1 month)
The moon’s shadow moves at 1700 km/hour (1,048 mi/hr) .
Maximum totality is ~7 ½ minutes.
Every place on Earth will see a total solar eclipse about every 400 years.
Solar Eclipses occur more frequently than lunar eclipses ( by 5:3).
There must be at least two solar eclipses every year.
There can be two solar eclipses in back to back months with a total lunar eclipse in between.
This triple eclipse can occur twice during an eclipse year (1935, 2160).
Seven eclipses is the maximum - 4 solar, 3 lunar (1982, 2485).
D(sun) = 870,000 mi (1.4M km)
(32.7’ to 31.6’)
D(moon) = 2,160 mi (3,476 km)
(33.5’ to 29.4’)
The moon is receding from the Earth by 3.8 cm / year.
When it has drifted another 12,552 mi (20,200 km), it will always be smaller than the sun (~1/2 billion years)
Earth’s day lengthens by 0.0016s / century
August 16, 1868: Helium is discovered in solar corona.
May 29, 1919: General relativity is verified
Total solar eclipses provide opportunity to study composition of corona.
Accurate timings allow calculation of solar dimensions.
Studies of ancient records reveal 0.001s slowing of Earth’s rotation
Oh leave the Wise our measures to collate One thing at least is certain, LIGHT has WEIGHT One thing is certain, and the rest debate -- Light-rays, when near the Sun, DO NOT GO STRAIGHT. - Arthur S. Eddington (1920)
1919 Solar Eclipse – Proving General Relativity