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Moon Phases & Eclipses. What patterns, motions, and events do we notice in the sky? What theories can we create to explain them? How can these theories be tested?. Observations of the Moon. Sequence of phases every “moonth” We always see the same “face”. Observations of the Moon.
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Moon Phases& Eclipses What patterns, motions, and events do we notice in the sky? What theories can we create to explain them? How can these theories be tested?
Observations of the Moon • Sequence of phases every “moonth” • We always see the same “face”
Observations of the Moon • Occasionally turns dark gray & even red! • Can seem bigger next to the horizon!
Phases repeat ~30 days • A “moonth” of time • Tied to religious calendars around the globe • Ramadan • Chinese New Year • Easter • Rosh Hashanah • Gudi Padwa & Vasant Panchami
Observations of the Moon • A sequence of repeated phases over about a “moonth”
Observations of the Moon • IS the phase the same on the same day around the world? • Do people in London see the same phase as we do in Hayward?
Observations of the Moon • IS the phase the same on the same day around the world? • Most people would say…… NO! • They are wrong! • Compare times • For Earth to rotate: hours • For the Moon to move & change phase: days
Observations of the Moon • Do people in both hemispheres see the same view? • Does an observer at Chabot see the same thing as someone in Santiago, Chile? • Most people would say…… er…YES? • They are wrong!
Phases are “reversed” in Southern Hemisphere! • Same side of moon is still lit by the sun • Observation from “down under” reverses view.
Seeing the moon from different places on Earth! Northern Hemisphere Southern Hemisphere
What theories can we develop? • WHY does the moon seem larger? • Because it IS larger? • Because it is an illusion • We see horizon different than zenith? • We don’t have a “reference” for Moon when it’s higher in the sky? • How can you TEST these hypotheses?
The Moon Illusion! The Moon DOES vary in distance….
The Moon Illusion! ….but not over a few hours!
The Moon Illusion! Perhaps… we don’t see the sky as symmetric – the horizon is farther away than the sky above us?
Solar Eclipses • Occur at NEW moon phase • While partial, a “bite” out of the Sun • Last 1+ hours • IF total… • Sky goes dark for a few minutes • See planets and stars near the sun • See Sun’s corona and chromosphere
Shadow of the moon covers small oval on Earth
Corona Chromosphere
Annual Solar Eclipse • Time-lapse series of photos • What time of day? • How long did this take? • Hint: Northern Hemisphere!
Lunar Eclipses • Occur at FULL moon phase • The Moon looks full, but dim • The Earth’s curved shadow falls across the moon • Last 2+ hours • IF total… • Moon can look red for an hour
At the start of a lunar eclipse, you can see the Earth’s Shape through its shadow…
Lunar Eclipse Time-Lapse Note the curved shadow of the Earth across the moon.
Predicting Eclipses • Eclipse “seasons” • About twice a year • Always at least (2) eclipses • One of each (lunar + solar) • About 2 weeks apart • Pattern repeats about 18 years for location and type
