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Homework #2
•
45.635 degrees is how many degrees, arcminutes, and arcseconds?
45 deg
 0.635(60)  38.1arcmin  38 arcmin
 0.1(60)  6arcsec
•
How many degrees, arcminutes, and arcseconds does the moon move across the sky in one
hour? (the lunar day is 24 hours and 48 minutes long)
24 hours 48 minutes  24.8 hours
The moon moves 360 degrees during that time so :
•
360 deg
 14.516129 deg/ hour  14o3058.06"
24.8hours
The moons diameter is about 30 arcminutes, so find out how long it takes for the moon to
travel its diameter.
0.5 deg
 0.034 hour
14.516129 deg/ hour
(0.034hour )  (60minutes/ho ur )  2.1 minutes  26
v  d/t  t  d/v 
Phases of Moon
• Half of the Moon is
illuminated by the
Sun and half is dark.
• We see a changing
combination of the
bright and dark
faces as the Moon
orbits Earth.
How to Simulate Lunar Phases
Lunar Motion
Phases of the Moon’s 29.5 day cycle
•
•
•
•
•
•
•
•
new
crescent
first quarter
gibbous
full
gibbous
last quarter
crescent
• Muku
• Külua
waxing
• ÿOlekükahi
• Huna
• Hoku
waning
• ÿOlekükahi
• Käloakükah
i
Hilo
Hoaka
Kükahi
Kükolu
Küpau
ÿOlekükahi
ÿOlekükolu
ÿOleküpau
Külua
ÿOlekülua
hoÿonui
Huna
Möhalu
Hoku
MäheaIani
Laÿaukülua
Laÿauküpau
Hua
Akua
Kulu
Laÿaukükahi
poepoe
ÿOlekükahi
Käloakülua
Mauli
ÿOlekülua
Käloapau
Muku
ÿOleküpau
Käloakükahi
Käne
Lono
ÿemi
We see only one side of the Moon
Synchronous rotation:
The Moon rotates exactly
once with each orbit.
This is why only one side
is visible from Earth.
Thought Question
It’s 9 A.M. You look up in the sky and see a
moon with half its face bright and half dark.
What phase is it?
A.
B.
C.
D.
First quarter
Waxing gibbous
Third quarter
Half moon
Thought Question
It’s 9 A.M. You look up in the sky and see a
moon with half its face bright and half dark.
What phase is it?
A.
B.
C.
D.
First quarter
Waxing gibbous
Third quarter
Half moon
What causes eclipses?
• The Earth and Moon cast shadows.
• When either passes through the other’s shadow, we
have an eclipse.
Lunar Eclipse
Lunar Eclipse
Solar Eclipse
Evolution of a Total Solar Eclipse
When can eclipses occur?
• Lunar eclipses can
occur only at full
moon.
• Lunar eclipses can
be penumbral,
partial, or total.
When can eclipses occur?
• Solar eclipses can occur
only at new moon.
• Solar eclipses can be partial,
total, or annular.
Why don’t we have an eclipse at every new and full
moon?
— The Moon’s orbit is tilted 5° to ecliptic plane.
— So we have about two eclipse seasons each year, with a lunar
eclipse at new moon and solar eclipse at full moon.
Summary: Two conditions must be met
to have an eclipse:
1. It must be a full moon (for a lunar eclipse) or a
new moon (for a solar eclipse).
AND
2. The Moon must be at or near one of the two
points in its orbit where it crosses the ecliptic
plane (its nodes).
Eclipse Predictions
• Eclipses recur in the approx. 18 yr, 11 1/3 day saros cycle
• But even then, eclipse location and type (e.g., partial, total) may
vary
Photo by Olaf Menkens (1999 Mauna Loa)
Planets Known in Ancient Times
• Mercury
Ukalialiÿi
– difficult to see; always close to Sun in sky
• Venus
Höküloa
– very bright when visible — morning or evening “star”
• Mars
Höküula
– noticeably red
• Jupiter
Hoÿomananalo
– very bright
• Saturn
– moderately bright
Makulu
Why did the ancient Greeks reject
the notion that the Earth orbits the
sun?
• It ran contrary to their senses.
• If the Earth rotated, then there should be a
“great wind” as we moved through the air.
• Greeks knew that we should
see stellar parallax if we
orbited the Sun – but they
could not detect it.
What is parallax? You use it every day…
Parallax Angle
Apparent shift of a star’s position due to the
Earth’s orbiting of the Sun
Possible reasons why stellar
parallax was undetectable:
1. Stars are so far away that stellar parallax is
too small for naked eye to notice
2. Earth does not orbit Sun; it is the center of
the universe
Unfortunately, with notable exceptions like Aristarchus, the
Greeks did not think the stars could be that far away, and
therefore rejected the correct explanation (1)…
Thus setting the stage for the long, historical showdown
between Earth-centered and Sun-centered systems.
Scientific Thinking
• It is a natural part of human behavior.
• We draw conclusions based on our experiences.
• Progress is made through “trial and error”.
Ancient Astronomy
• Many cultures throughout the world practiced astronomy.
• They made careful observations of the sky.
• Over a period of time, they would notice the cyclic
motions of:
–
–
–
–
Sun
Moon
planets
celestial sphere (stars)
Stonehenge (completed 1550 BC)
This famous structure in England was used as an observatory.
• If you stand in the middle:
– the directions of sunrise &
sunset on the solstices is
marked.
– the directions of extreme moon
rise & set are marked.
• The Aubrey holes are believed to
be an analog eclipse computer.