Transcript The REAL OCCULT:

The REAL OCCULT:
Lunar & Solar Eclipses and Asteroid
& Stellar Disappearances Sometimes
Involving Luna
By Dr. Harold Williams
of Montgomery College Planetarium
http://montgomerycollege.edu/Departments/planet/
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Types of Occultations
Lunar Eclipse,
Solar Eclipse,
Asteroidial Occultation,
Lunar Occultation,
– Grazing Lunar Occultation
– Planet Lunar Occultation
• Transit of Planet across the Sun
– Transit of Mercury (next one November 8, 2006)
– Transit of Venus (June 8, 2004, next one June 6, 2012)
• Planet disappearing behind moon
Lunar Eclipse
• Lunar Eclipse, shadow of the earth gets in front of the
full moon at night time.
• When the moon, earth, and sun align in that order at
a node.
• The reason we do not have 13 eclipses a year is
because the orbit of the earth around the sun, the
ecliptic, and the orbit of the moon around the earth
are inclined by around 5 degrees, they are not
aligned (it would be improbable if they were perfectly
aligned instead of being close).
A Total Lunar Eclipse (1)
A Total Lunar Eclipse (2)
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 Earth’s
atmosphere.
Lunar Eclipses
Earth’s
shadow
consists of a
zone of partial
shadow, the
Penumbra,
and a zone of
full shadow,
the Umbra.
If the moon passes through Earth’s full shadow
(Umbra), we see a lunar eclipse.
If the entire surface of the moon enters
the Umbra, the lunar eclipse is total.
Solar Eclipse
• Solar Eclipse, new moon gets in front of the sun in the day time.
• When the earth, moon, and sun align in that order at a node.
• The reason we do not have an eclipse every month is again,
because of the 5 degree inclination of the orbit of the earth
around the sun and the orbit of the moon around the earth.
• Fred Espenak's Eclipse Pages at
http:/sunearth.gsfc.nasa.gov/eclipse/eclipse.html, best general
scientific source of eclipse maps, dates, and general data for
both lunar and solar eclipses. Everyone uses Fred Espenak, he
is without peer for specific eclipse information.
• Wendy Carlos Eclipse Pages at
http://www.wendycarlos.com/eclipse.html , some of the finest
pictures taken by a true artist of solar eclipses and music.
Diamond Ring Effect
Solar Atmosphere Revealed
Solar Eclipses
The sun appears approx. as large in the sky (same angular
diameter ~ 0.50) as the moon.

When the moon passes in front of the sun, the moon can
cover the sun completely, causing a total solar eclipse.
Solar Eclise Viewing
• While lunar eclipses are inherently safe, Solar
Eclipses, the partial phases, are of course dangerous
to human eyes. Of course, they are no more
dangerous than looking at the sun on any day time
that the sun is visible. Toddlers and grasshoppers
avoid blinding themselves every day when the sun is
visible by not looking directly at it.
• If it hurts don't do it.
• Safe Solar Filters
Solar Filters
Places to get safe solar filters
• http://www.tropicalsails.com/shades.htm
• http://www.eclipse1999.com/
• http://www.weatherman.com/ECLIPSE2000.htm
• 301-482-0000 or 301-482-2210 Hands on Optics in Damascus,
MD 20872, http://www.handsonoptics.com . During the total
solar eclipse though it is quite safe to look directly at the sun. I
have spent a total of 4 minutes looking directly at the sun during
two total solar eclipses; and it has not damaged my eyes.
Earth and Moon’s Orbits Are Slightly
Elliptical
Apogee =
position furthest
away from Earth
Perihelion = position
closest to the sun
Earth
Perigee = position
closest to Earth
Moon
Sun
(Eccentricities greatly exaggerated!)
Aphelion
= position
furthest
away
from the
sun
Annular Solar Eclipses
When Earth is near perihelion, and
the moon is near apogee, we see
an annular solar eclipse.
Perigee
Apogee
Perihelion
Aphelion
The angular
sizes of the
moon and the
sun vary,
depending on
their distance
from Earth.
Annular Solar Eclipses (2)
Almost total, annular eclipse of May 30, 1984
Conditions for Eclipses (1)
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.
Conditions for Eclipses (2)
Eclipses occur in a cyclic pattern.
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Saros cycle: 18 years, 11 days, 8 hours
Asteroidial Occultation
• An asteroid orbiting the sun sometimes get in
front of a star as seen from the earth.
• This type of Asteroidial occultation is used to
measure the size of the asteroid
• and to tell whether it has an any moons
orbiting the asteroid.
• Here the alignment is earth, asteroid, and star
in that order.
• http://scienceworld.wolfram.com/astronomy/Asteroid.html
29 October 2005 790 Pretoria
Asteroidial Occulation Updates
• http://www.asteroidoccultation.com/
Lunar Occultation
• Moon traveling in it orbit around the earth occults stars.
• When it occurs near the top or bottom of the moon this is called
a Grazing Lunar Occultation. As the star gazes behind the
lunar edge profile the star appears to go out and then back on
when it appears from a deep lunar valley.
• Grazing lunar occultations are used to determine the lunar edge
profile very accurately so that when solar eclipses happen and
the last part of the photosphere appears in deep lunar valleys,
forming Baily's Beads. The timing of these Baily's beads can
be used to tell whether the sun is getting larger or smaller over
time, by comparing Baily's beads timing from solar eclipse to
solar eclipse. This is basic long term research that answers
extremely important critical questions about the size of the sun
and future changes in our climate on earth. Global warming or
cooling and all of that sort of stuff.
• Moon can get in from of a planet like Saturn (seen it).
Lunar Occultation Links
• http://www.lunaroccultations.com/iota/iotandx.htm
February 20, 2002 Moon occults
Saturn
• http://antwrp.gsfc.nasa.gov/apod/ap020222.
html Astronomy Picture of the Day
February 22, 2002.
Transist of Venus Across the Disk of
the Sun June 8, 2004
• http://www.montgomerycollege.edu/Departments/
planet/planet/VenusTransit.html
• http://montgomerycollege.edu/Departments/planet
/planet/Mercurytransit2006.html Transit of
Mercury across the disk of the sun November 8,
2006.
• http://sunearth.gsfc.nasa.gov/eclipse/transit/venus/
Map2012-2.GIF Visibility of June 6, 2012 transit
of Venus across the Sun.