Cycles of the Sky

Chapter 3:

A Total Lunar Eclipse (II)

A total lunar eclipse can last up to 1 hour and 40

min.

During a total eclipse, the moon

has a faint, red glow, reflecting

sun light scattered in the Earth’s atmosphere.

Typically,

1 or 2

lunar eclipses

per year.

Solar Eclipses (I)

The angular diameter of the moon (~ 0.5o) is almost exactly the same as that of the sun.

This is a pure chance coincidence. The moon’s linear diameter is much smaller than that of the sun.

Total Solar Eclipse

The moon’s shadow sweeps across the Earth, over points

from where we can see a solar eclipse.

Total Solar Eclipse

During a total solar eclipse, the solar chromosphere, corona, and prominences

can be seen.

The Diamond Ring Effect

Earth’s and Moon’s orbits are slightly elliptical:

Sun

Earth

Moon

(Eccentricities greatly exaggerated!)

Perihelion = position closest to the sun

Aphelion = position furthest

away from the sun

Perigee = position closest to Earth

Apogee = position furthest away from

Earth

Annular Solar EclipsesThe angular sizes of the Moon and

the Sun vary, depending on their distance

from Earth.

When the Earth is near perihelion, and the Moon is

near apogee, we see an annular solar eclipse.

Perigee Apogee Perihelion Aphelion

Almost total, annular eclipse of May 30, 1984

Approximately 1 total solar eclipse per year

Very Important Warning:Never observe the sun directly with your bare eyes,

not even during a partial solar eclipse!

Use specially designed solar

viewing shades, solar filters, or a

projection technique.

Conditions for Eclipses (I)

The Moon’s orbit is inclined against the ecliptic by ~ 50.

A solar eclipse can only occur if the Moon passes a node near New Moon.

A lunar eclipse can only occur if the Moon passes a node near Full Moon.

The Origin of Modern Astronomy

Chapter 4: