Astronomy 1 – Fall 2014 Lecture 2; October 7, 2014 UCSB Astro 1 - Martin Set your alarm clock for 3am to see tonight’s eclipse!

Previously on Astro-1 Goal 1 – The big picture –The Universe is huge; we will make a “Grand Tour” Goal 2 – The scientific method –Demarcation: what is science? –Falsification: how do you test scientific theories? –Corroboration: what is a “good” scientific theory? Goal 3 – Learning scientific language –Science terms have very precise definitions, with sometimes somewhat different meaning than in the current language (e.g., Powers of ten; Units;Small Angle Formula) UCSB Astro 1 - Martin2

Today on Astro-1 Constellations & Celestial Sphere Seasons The moon’s orbit Lunar eclipses Solar eclipses Ancient studies of moon and sun’s orbit UCSB Astro 1 - Martin3

The Night Sky UCSB Astro 1 - Martin4

The sky is divided into 88 constellations, but the stars are at different distances UCSB Astro 1 - Martin5

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The diurnal (daily) motion of the stars. UCSB Astro 1 - Martin8

The diurnal (daily) motion of the stars. UCSB Astro 1 - Martin9

The night sky changes during the year How fast does the position of the Earth move around the sun every month? UCSB Astro 1 - Martin10

The imaginary celestial sphere. The celestial equator and poles are projections of the Earth’s axis of rotation out into space. UCSB Astro 1 - Martin11

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Seasons UCSB Astro 1 - Martin13

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Ecliptic plane: the plane in which the Earth moves around the Sun. UCSB Astro 1 - Martin16

Ecliptic plane and the ecliptic: just a matter of perspective UCSB Astro 1 - Martin17

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Midight Sun from Arctic Circle UCSB Astro 1 - Martin 22 What direction is the photographer facing? A.North B.South C.East D.West E.None of the above. This photograph was photoshopped.

The Moon’s Orbit UCSB Astro 1 - Martin23

This picture of the Earth and the Moon was taken in 1992 by the Galileo spacecraft on its way toward Jupiter. UCSB Astro 1 - Martin24

What you see from earth UCSB Astro 1 - Martin25

When do you see the moon in the morning sky? UCSB Astro 1 - Martin26

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Sidereal month: the time the Moon takes to complete one full revolution around the Earth with respect to the background stars: days Synodic (lunar) month: Time from one new moon to the next: 29½ days. UCSB Astro 1 - Martin28

Why don’t we have eclipses every month? UCSB Astro 1 - Martin29

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Lunar eclipse: Moon is in the shadow of the Earth UCSB Astro 1 - Martin31

Lunar eclipse: three types UCSB Astro 1 - Martin32

The Moon moving through the Earth’s umbra over 3 hours. UCSB Astro 1 - Martin33

On average, two or three lunar eclipses occur in a year. Of all lunar eclipses, roughly one-third are total, one-third are partial, and one-third are penumbral.

Tonight’s Eclipse UCSB Astro 1 - Martin35

How did ancient astronomers discover that the Earth is round? UCSB Astro 1 - Martin36

Solar eclipse UCSB Astro 1 - Martin37

A total solar eclipse. The moon passes in front of the sun. UCSB Astro 1 - Martin38

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During a total solar eclipse, the tip of the Moon’s shadow traces an eclipse path across the Earth’s surface. People within the eclipse path see a total solar eclipse as the tip moves over them. Anyone within the penumbra sees only a partial eclipse. Photo from Russian space station Mir (of same eclipse in previous 2 slides)! UCSB Astro 1 - Martin41

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Annular solar eclipse. UCSB Astro 1 - Martin43

There are at least two, but never more than five solar eclipses each year.

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Eratosthenes’s determined the diameter of the Earth around 200 B.C.! Distance from Alexandria to Syene was said to be about 5000 stades, so Earth’s circumference was computed to be 50 × 5000 = 250,000 stades UCSB Astro 1 - Martin46

Aristarchus determined distances to sun and moon, and determined sizes of moon and sun relative to Earth around 280 B.C.! He got the answer wrong because of poor measurements, but had the right technique. UCSB Astro 1 - Martin47

Summary The night sky Seasons –Why is it colder in winteπr? Lunar Phases: –How do they arise? Length of the Month: –How long does it take for the moon to go around the Earth? The Moon’s Orbit: –Why don’t we have lunar eclipses every month? Solar eclipses –What kind of solar eclipses are there? When do they happen? UCSB Astro 1 - Martin49

Homework – Due 10/13/14 On your own: answer all the review questions in chapter 2-3. To TAs: answer questions 2.40, 2.46, 3.31, 3.43 UCSB Astro 1 - Martin50