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ASTR 1210, Week 2 of Notes

by: Raleigh Zook

ASTR 1210, Week 2 of Notes ASTR 1210

Marketplace > University of Virginia > Astronomy > ASTR 1210 > ASTR 1210 Week 2 of Notes
Raleigh Zook
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About this Document

These notes go over the Moon relative to the Earth, Seasons, and Motions of the Earth
Introduction to the Sky and Solar System
Remy Indebebetouw
Class Notes
astronomy, stars, seasons, moon, EARTH




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This 5 page Class Notes was uploaded by Raleigh Zook on Tuesday February 2, 2016. The Class Notes belongs to ASTR 1210 at University of Virginia taught by Remy Indebebetouw in Spring 2016. Since its upload, it has received 18 views. For similar materials see Introduction to the Sky and Solar System in Astronomy at University of Virginia.

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Date Created: 02/02/16
ASTR Lecture 3 Notes H3: Get stellarium (or similar program) due Feb. 9—give in class Motions Throughout the Year • During the year, the Sun’s position changes daily. • Universe does not orbit around Earth (or even our solar system) • Summer solstice: Sun directly overhead; Peaking higher at the meridian o Solstices and equinox line parallel to one another • Analemma: Sun’s position at noon (A means to determine the time); Pattern o Sundials and buildingsmap it out o The highest point, Summer Solstice; The lowest point, Winter Solstice o The Earth’s orbit is not completely circular—it is elliptical --Pointed in the same direction, but not same relation to the Sun, that is why the Sun’s position moves throughout each day, but more vividly between each season • Earth is tilted 23.5°—One of the reasons for season change o Orientation in relation to the sun changes since the Earth’s axis is pointed in the same direction Equator of Earth at solstice, light is coming straight down o Same energy/time spread out over area 1/(Cos23.5) § The area (since it is slanted) is 1.09x larger • Large-scale weather circulation—Equator’s atmosphere is heated, while Poles are cooled. This circulates between them. How come distance does not matter for seasons? • The distance between the Earth and Sun only has a variation of 3% (Closest and furthest), which is very small ▯ • Ener▯y received ~ 1/???????????????????????????????? 1.03 =1.06 Other Planets’ Seasons • Venus: 2.6° tilt o Very little variation in seasons o Can pose a problem • Uranus: 82° tilt o Extreme variation in seasons o 21 years of: “normal” days and nights, nighttime in Northern Hemisphere, “”normal” days and nights”, daytime in the Northern Hemisphere o 84 years to revolve around the Sun • “Alien Life May Depend on Planetary Tilt” –Adam Hadhazy, 2012 • Some planets’ tilts wobble, or “precess” • Different tilts and different ellipticities Seasonal Terminology • Solstices: Winter and Summer (The “extremes”) Equinoxes: Fall and Spring (Equal day, equal night) o These are recognized by the Sun’s position relative to the Earth • Zodiac: The stars visible on the equinox—at noon o That constellation is not seen bc it appears during the day Orientation of Earth’s Axis Changes over Time Precession: Occurs about 26,000 years • Due to friction s • North Celestial Pole will not point at Polaris—it will not always be the North Star • Equinox positions shift around the orbit o Spring equinox—If it was once in Aries, then it would now be in Pisces o Seasons would be opposite • Analogy to a spinning top • Constellations will distort Constellations • Stay the same if on same latitude (Longitude does not matter for viewing constellations), however, constellations are seen differently at different latitude positions Lecture 4: Chapter 2 of “The Cosmic Perspective”; Week 2 February 4, 2016 Phases of the Moon • The side of the moon visibly seen is illuminated by the Sun (Many different faces are seen, BUT only one side of the Moon is seen) • 29.5 day cycle: o New Moon—Moon not seen § Rises at sunrise (with the sun) and sets at sunset (like the sun) § Sun shines on opposite side of the Moon (Which makes the side seen during this phase dark) o Crescent o First quarter o Gibbous o Full Moon—The side of the moon visible is fully seen o Gibbous o Last Quarter o Crescent • Waxing: When the Moon is becoming fuller o Rises later each day and it is visible in the afternoon/evening • Waning: When the Moon appears to become “less” visible o Sets later every day and is visible in the late night/morning • Synchronous Rotation o The reason for why only one side of the Moon is seen o Moon fully rotates in one month at the same speed of the Earth • The side of the moon not visible has more craters, because the Earth is providing some protection to the other side (Sort of like a buffer, since it would be harder for an asteroid to hit that side from that angle) • There is a satellite between Earth and the Sun, which allows us to see a little portion of the dark side Lunar Effects • Tides o The side parallel to the moon undergoes high tide (and on the opposite side of the Earth), while low tide occurs at the two other ends o Tidal bulge offset since the Earth rotates much faster than the Moon does § Tidal effects are slowing the Earth’s rotation down § The amount of power that this is generating is draining the Earth of 6 terawatts Ø Laser ranging used to determined lunar distance --Apache Point Observatory Lunar Laser-ranging Operation (New Mexico) • Lunatics o There is some evidence that animals have lunar cycles o Increased light is good for predators, but bad for prey o Marine animals experience tidal effects, such as foraging § Access for food, feeding habits change o Mental health patient behaviour and emergency room admittance—No strong correlation between these and lunar cycles o If spent a lot of time outside, menstrual cycle may be affected, ovulation occurring in the dark phase—Moderate statistical evidence Eclipses • When the Earth and Moon pass through each other’s shadows, then an eclipse may occur • Penumbra and Umbra • Solar Eclipse o Occurs when Moon is in the phase as a New Moon o Partial, total, or penumbral o The moon is tilted at 5°, so there are possible two eclipse seasons every year (Including both lunar and solar eclipses) o There are two nodes (points in the Moon’s orbit), which intersect with the Earth’s ecliptic plane. Either needs to be at or near these nodes in order for an eclipse to occur. o Moon’s shadow is on Earth • Lunar Eclipse o Moon at Full Moon o Earth’s shadow is covering the Moon • Predictions o Occur around every 18 years, 11 1/3 day saros cycle § Location and the type of eclipse differs, however Ancient Mystery • Apparent Retrograde Motion: Planets typically move eastward, in relation to the stars, BUT occasionally move westward, in relation to the stars, for a few weeks o Perception—Earth’s orbit is smaller, which causes the planets to appear like they are moving backward o Seen when the Earth passes by a planet in orbit o Ancient Greeks rejected this (correct) explanation, because they believed the Earth was the center of the universe § They were unable to comprehend stellar parallax § Believed stars could not be that far away to make this parallax phenomenon occur Review Celestial Navigation • How to determine latitude? o How far from equator o Daytime: In relation to meridian crossing, the Sun’s altitude would be close to noon Necessary to know the day of year to know which season—height of Sun in the sky o Nighttime: Altitude of the celestial pole is the latitude o Arctic Circle (66.5°N) and Tropic of Cancer (23.5°N) o Cross-staff or sextant used for navigation • How to determine longitude? o Time difference from current location to a fixed location. Local time can be calculated from stars. An accurate clock is necessary to obtain an accurate calculation of longitude o 1714 Longitude Act • Triangulation: Angle of top of cliff to another place, with the height of the cliff, geometry can be used to determine self-location • GPS and General Relativity o Trilateration: Uses distances as references o Susceptible to cyber attacks, which is why sextants are now being employed to decrease the chance of this happening


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