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Homework Set #2 8/30/17 Due 9/11/17 Chapter 3 Review Questions 1, 2, 9

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1 Homework Set #2 8/30/17 Due 9/11/17 Chapter 3 Review Questions 1, 2, 9
PHYS Astronomy Homework Set #2 8/30/17 Due 9/11/17 Chapter 3 Review Questions 1, 2, 9 Problems 1, 7, 9, 11 Using the small angle formula, calculate the angular size of Venus as viewed from Earth at inferior conjunction.

2 PHYS Astronomy

3 PHYS Astronomy Lunar Phases Moon’s appearance and rise and set times change with the cycle of the lunar phases The sun illuminates one side (half) of the moon - appearance varies with side of moon facing the Earth - the angle between the sun-Earth line and the Earth-moon line.

4 Phases of the Moon Animation
PHYS Astronomy Phases of the Moon Animation

5 Lunar Phase Terminology
PHYS Astronomy Lunar Phase Terminology Phases of the Moon’s 29.5 day cycle new crescent first quarter gibbous full last quarter waxing waning

6 PHYS Astronomy Lunar Phases

7 New Moon  First Quarter  Full Moon
PHYS Astronomy New Moon  First Quarter  Full Moon

8 Full Moon  Third Quarter  New Moon
PHYS Astronomy Full Moon  Third Quarter  New Moon

9 Moon Rise and Set Animation
PHYS Astronomy Moon Rise and Set Animation

10 What’s wrong with this moon (at night)?
PHYS Astronomy What’s wrong with this moon (at night)?

11 PHYS Astronomy Earthshine The dark portion of the lunar face is not totally dark - you can see the outline of the full face of the Moon even when the Moon is not full - in particular the crescent phase. Because the crescent phase is nearly a new moon as seen from Earth, the Earth is nearly full as viewed from the moon. The light of Earth illuminates the night moonscape - just as the full moon illuminates the Earth landscape. Because Earth is much larger than the Moon, the full earth is much bigger and brighter in the lunar sky than the full moon is in Earth's sky. This faint light illuminating the “dark” portion of the Moon's face is often called the ashen light or earthshine.

12 Eclipses The Earth & Moon cast shadows.
PHYS Astronomy Eclipses The Earth & Moon cast shadows. When either passes through the other’s shadow, we have an eclipse Solar eclipse - when Earth passes through Moon’s shadow - occurs at new Moon Lunar eclipse - When Moon passes through Earth’s shadow - occurs at full Moon

13 PHYS Astronomy Shadows The shadow cast by an object in sunlight. Two distinct regions - sunlight is fully blocked in the umbra and partially blocked in the penumbra. Umbral shadow totally dark, penumbral shadow only slightly darker than no shadow.

14 Types of Lunar Eclipses
PHYS Astronomy Types of Lunar Eclipses Total Moon in Earth’s umbra - maximum duration in total eclipse region minutes Partial Moon partly in Earth’s umbra Penumbra Moon in Earth’s penumbra - virtually undetectable

15 Lunar Eclipses: Present - 2020
PHYS Astronomy Lunar Eclipses: Present There are typically 2 partial or total lunar eclipses per year.

16 PHYS Astronomy As viewed from Earth, Earth's shadow can be imagined as two concentric circles. - type of lunar eclipse is defined by the path taken by the Moon as it passes through Earth's shadow.

17 - one on ascending node and one on descending node
PHYS Astronomy Generally two lunar eclipses per year, separated by 6 synodic months (177 days) - one on ascending node and one on descending node Descending node Ascending node

18 PHYS Astronomy

19 Lunar Eclipses Animation
PHYS Astronomy Lunar Eclipses Animation

20 Evolution of Total Lunar Eclipse Animation
PHYS Astronomy Evolution of Total Lunar Eclipse Animation

21 PHYS Astronomy Total Lunar Eclipse 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.

22 The Small-Angle Formula
PHYS Astronomy The Small-Angle Formula - a mathematical approximation - relates the linear size (D) of an object to its angular size (α) and its distance from the observer (d) - is a valid approximation if α is small. d α D

23 PHYS Astronomy Solar Eclipses We are fortunate - the sun appears approximately 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.

24 Types of Solar Eclipses
PHYS Astronomy Types of Solar Eclipses Total If the eclipse occurs when the Moon is close to the Earth - umbra covers small area of Earth’s surface (no more than 270 km in diameter) - anyone in this area sees a total eclipse. Partial Anybody in penumbral shadow (about km in diameter) will see a partial eclipse. Annular If the eclipse occurs when the Moon is far from the Earth - the umbra does not reach the Earth, only the penumbra. Anyone in this area directly behind the umbra sees an annular eclipse

25 Evolution of a Partial Solar Eclipse Animation
PHYS Astronomy Evolution of a Partial Solar Eclipse Animation

26 Evolution of a Total Solar Eclipse Movie
PHYS Astronomy Evolution of a Total Solar Eclipse Movie

27 Earth and Moon’s Orbits Are Slightly Elliptical
PHYS Astronomy Earth and Moon’s Orbits Are Slightly Elliptical Apogee = position furthest away from Earth Earth Perihelion = position closest to the sun Moon Perigee = position closest to Earth Sun Aphelion = position furthest away from the sun (Eccentricities greatly exaggerated!)

28 Annular Solar Eclipses
PHYS Astronomy Annular Solar Eclipses When Earth is near perihelion, and the moon is near apogee, we see an annular solar eclipse. The angular sizes of the moon and the sun vary, depending on their distance from Earth. Perigee Apogee Aphelion Perihelion

29 Almost total, annular eclipse of May 30, 1984
PHYS Astronomy Almost total, annular eclipse of May 30, 1984

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