Transcript Eclipses Eclipse: BrainPOP • http://www.brainpop.com/science/space/ecli pse/ Eclipse worksheet for BrainPOP • http://www.middleschoolscience.com/BrainP OPeclipse.pdf Eclipse worksheet • http://www.middleschoolscience.com/eclipse. pdf.

Eclipses
Eclipse: BrainPOP
• http://www.brainpop.com/science/space/ecli
pse/
Eclipse worksheet for BrainPOP
• http://www.middleschoolscience.com/BrainP
OPeclipse.pdf
Eclipse worksheet
• http://www.middleschoolscience.com/eclipse.
pdf
• The changing phase of the Moon…
• The un-changing face of the Moon…
• Eclipses
– Lunar Eclipses
– Solar Eclipses
Solar and Lunar Eclipses
Eclipse:
The total or partial obscuring
of one celestial body by
another…
The obscuration can be either
• One celestial body blocking
the view to the other:
– Solar eclipse---Moon
blocking Earth’s view to the
Sun…
• One celestial body is in the
shadow of another:
– Lunar eclipse---Moon is in
the shadow of the Earth…
Lunar eclipse image from http://www.mreclipse.com
Solar Eclipses
The solar corona is
revealed during a total
solar eclipse
• The corona is about one
millionth times fainter
than the disk of the Sun.
• Similar to observing stars
next to the Sun, the light
from the disk must be
blocked (by the moon, or
by special occulter in the
telescope) before we can
see the solar corona.
What Causes Eclipse?
• The Earth and Moon cast shadows.
• When either passes through the other’s shadow, we have an eclipse.
• Because the Sun is an extended bright object, there are two different
regions of the shadow:
– Penumbra is partially illuminated
– Umbra is completely dark
Click on the image to start animation
Lunar eclipses
• Lunar eclipses happens
when the Moon passes
through the shadow of the
Earth
– Everybody on the night side
of Earth can see the lunar
eclipse.
• Lunar eclipses can be
partial, penumbral, or
total.
• Lunar eclipses can occur
only at full moon.
Click on the image to start animation
Solar eclipses
• Solar eclipses occur when
the shadow of the Moon
falls on the surface of
Earth
– Only people in the shadow
can see the eclipse.
• Solar eclipses can be
partial, annular, or total.
• Solar eclipses can occur
only at new moon.
Click on the image to start animation
Eclipse Path
When total or ring solar eclipse happens…
• The diameter of the umbra of lunar shadow is no more than
270 km…you can see the total eclipse only if you are in a very
narrow and long eclipse path.
– In the 1990 total eclipse that passed through the big island of Hawaii,
people on Maui and Oahu cannot see the total eclipse!
• The diameter of the penumbra of the lunar shadow is about
7000 km (Earth’s diameter is about 13,000 km). So, the region
that partial eclipse can be seen is quite large…and people on
Maui and Oahu could see partial eclipse!
 Eclipse Prediction
Total Solar Eclipse
What’s the difference between a total and ring eclipse?
The distance between the Earth and the Sun.
You don’t see the Sun at all if
you are in the umbra
Sun
Click on the Sun to
start animation
Moon
You see the partial Sun if
you are in the penumbra
You see the whole Sun
outside of the shadow
Surface of the Earth
Ring Eclipse
• Ring eclipse happens when the Moon does not
completely block the Sun, like partial eclipses…
• The umbra is NOT
completely dark!
• You see a ring if you are
in here
Sun
Click on the Sun to start
animation
Surface of the Earth
Moon
You see the partial Sun if
you are in the penumbra
You see the whole Sun if you are
outside of the shadow
Distance Between the Moon and Earth
• Like the Earth’s orbit
around the Sun, the orbit of
the Moon around the Earth
is not a perfect circle.
– Eccentricity of Earth’s orbit is
~ 0.016
• The distance between the
Moon and Earth change.
This is why we have total
and ring eclipses
– Eccentricity of Lunar orbit is
~ 0.05
Solar Eclipses: A Coincidence?
• What if the Moon is closer (say twice as close)
to the Earth?
• What if the Moon is farther (say twice as far)
away from the Earth?
• What if the Moon is two-time bigger?
• What if the Moon is two-time smaller?
How Often Does Eclipse Occur?
• Do we have one solar and one lunar eclipse every
month, since we have a full and a new Moon every
month?
Click on the image to start animation
How Often Does Eclipse Occur?
• Do we have one solar and one lunar eclipse every six month,
when the nodes line-up with the Earth-Moon line?
– NO! Because of the precession of the lunar orbit!
Nodes: the two
points when the
Moon crosses the
ecliptic plane
• Only when the
nodes are
located right
between the
Earth-Sun line
can solar
eclipses occur.
The Precession of Lunar Orbit
• The orbital motion of the
Moon around Earth slowly
precesses with an 18.6 year
cycle as the Earth orbit the
Sun…
Click on the image to start animation
How Often Does Eclipse Occur?
•
The combination of these motions of the Moon
1. 29 ½ day orbital motion around Earth,
2. 5º tilt of the orbit w.r.t. the ecliptic, and
3. Precession of the lunar orbit w.r.t. the ecliptic,
•
•
Eclipse occurs with a period of about 18 years and
11-1/3 days  Soras cycle
But these eclipses don’t happen at exactly the same
location over the Soras cycle…
Solar Eclipse Forecast
Solar eclipses from 2004 to 2030
Knowing the orbit
of the Earth and
the Moon, we can
now calculate the
time and path of
solar eclipses with
great accuracy.
Back to Eclipse Path
Eclipses: Summary
•
•
The parties involved: Sun, Moon, and Earth
Motion of the Moon around Earth:
1. 29 ½ day revolution of the Moon around the Sun
2. Tilt (~5º) of the lunar orbit (around the Earth) w.r.t. the Ecliptic plane (Earth’s
orbital plane around the Sun)
3. The precession of the lunar orbit w.r.t. Earth-Sun direction
•
•
Solar eclipse happens when the Moon is between the Earth and the Sun.
The size and distance of the Moon need to be just right for us to see total
eclipse.
–
–
•
The changing distance between the Earth and the Moon explains the
occurrences of the total and ring solar eclipses.
The changing distance between the Earth and the Sun, and the Earth and the
Moon explains the difference in the duration of the solar eclipses.
Lunar eclipse happens when Earth is between the Moon and the Sun.