An educational slideshow by Lou Mayo of NASA and GSFC outlining the astronomy, mathematics, and culture of Solar Eclipses. The presentation balances historical perspective with current scientific research, and adds a healthy does of popular interest for non-scientific audiences.

1. Solar Eclipses
Through Space
and Time
Cycles in the Sky
Lou Mayo, NASA/GSFC

9. Chinese astrologers
wrote of an eclipse
occurring over 4000
years ago.
Historians and
astronomers believe
that this was an eclipse
that happened on 22
October 2134 B.C.
Two astrologers at the
time, Hsi and Ho, had
apparently failed to
predict this eclipse,
and so were beheaded.

10. "Nothing can be sworn
impossible since Zeus
made night during mid-
day, hiding the light of
the shining Sun."
- Archilochus 648 BC

11. Solar eclipse have been generally explained in one of four ways:
• A celestial being, usually a monster, attempts to destroy the Sun
• The Sun fights with its lover the Moon
• The Sun and the Moon make love and discreetly hide themselves in
darkness
• The Sun grows angry, sad, sick, or neglectful
Littmann and Willcox, “Totality”
Norse mythology: the wolflike giant Sköll
follows the Sun hoping to devour it.
Ancient Egypt: the evil god Set was
thought to have leapt into the eye of the
Sun god, Horus.
Ancient China: A heavenly dog ate the
Sun.
Chippewa Indians shot flaming arrows at
the Sun hoping to rekindle the flames.
Ancient Meaning

12. BASIC ECLIPSE GEOMETRY

16. Perigee Apogee

18. When do we get an eclipse?
• 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.

19. Saros Cycle
• “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)

21. Fun Eclipse Facts
• 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).

22. Will we always have
total solar eclipses?
• 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

23. 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
ECLIPSE SCIENCE

24. 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

27. A Perfect Day

29. Solar Eclipse
August 11, 1999
Soissons, France

30. March 29, 2006

35. 1882 Transit
(USNO)

37. Application to Exo Planet
Studies
HD 209458 (mv = +7.7) in Pegasus

38. Solar Eclipse Activity
GOALS:
To simulate a solar eclipse
To understand the concept of angular size
To make estimates of absolute and
relative size
MATERIALS:
Yard or meter stick (don't
confuse your units!)
Construction paper
Tape
Scissors
CD-ROM
Pencil
Black and yellow markers

39. PROCEDURE:
1. MAKE THE SUN: Lay the CD on the construction paper and trace
around its outer edge. Then trace around the center hole.
2. Draw two lines (a tab) down from the CD and fanning out so the CD
circle and tab look like the picture on this slide. The tab will be used to
mount the CD circle on the yard/meter stick.
3. Cut out the large CD circle and connected tab. This will represent
the sun. The small circle in the center will represent the size of the
moon (of course, this is not to scale).
4. Color the CD circle yellow (for the sun) and the small center circle
black.
5. MAKE THE MOON: Now, on a different piece of construction paper,
trace just the center hole in the CD. Make the same kind of tab for this
circle as you did for the sun circle. Make the tab a bit longer than the
sun's tab. Color the moon black and cut it out.
6. ASSEMBLE: Bend the sun and moon back 90 degrees from their
tabs at the BASE of the tab. Wrap the fanned out portion of the tabs
around the yard/meter stick and tape the ends together. The sun
should be near the end of the stick and the moon should be near the
front. The sun and moon should now be able to slide up and down the
stick.

40. Moon
Sun

41. Now, holding the yard/meter stick against your cheek, sight down the
stick. The smaller moon circle will cover some portion of the sun circle.
Slide the moon back and forth to a place where it just covers the sun.
Looking at the yard/meter stick, note the distance (in inches or cm) of the
moon. Then note the distance of the sun. Finally, measure the diameter
of the moon. You can now create similar triangles that will help you
answer the following questions:
1. On the yard/meter stick, how much further
away is the sun than the moon?
2. Given the diameter of the moon, can you
predict the diameter of the sun?
3. In space, our real moon has a diameter of
3,476 km and is on average 384,400 km
from Earth. The sun is about 149,600,000
km from the Earth. How many times further
is the sun then the moon? What would you
estimate to be the diameter of the sun?
4. What is the angular size of the sun? moon?
(hint: construct right triangles and use trig)