Lecture 2

# Lecture 2 - the North Celestial Pole sweeps a large circle...

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9/24/09 BRIGHTON FIELD 9-11PM BEHIND GYM (2115 COMM AVE) RECAP Fact: The stars and sun appear to go from east to west in the sky because of Earth’s daily spin around its axis (in counter-clockwise direction) Fact: Observed over the course of many nights, the stars appear to change location in the sky from east to west because of Earth’s yearly orbit around the sun (again, counter-clockwise) Fact: The seasons are an effect of the tilt of Earth’s axis, which causes the sun to appear higher in the sky at certain times of the year (summer) and lower at others (winter). Fact: Precession causes the direction of the North Celestial Pole (the earth’s rotational axis) to change over a long period of time, sweeping out a circle on the Celestial Sphere every 26,000 years. Precession – the slow changing of direction of the Earth’s axis with respect to the Celestial Sphere

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Unformatted text preview: the North Celestial Pole sweeps a large circle in sky every 26,000 years Measuring the Sky: On Earth In Sky (Celestial Sphere) Coordinates (x,y) Latitude declination (Dec) Longitude right ascension (RA) Units Lat: degrees N/S degrees, arc minutes, arc seconds Long: degrees E/W hours, minutes, seconds Zero Points Lat: Equator Celestial Equator Long: Prime Meridian “First Point of Aries” – point in sky where sun appears on 3/21 Declination: 1 degree = 1/360 of sky 1 arc minute (1’) = 1/60 of a degree 1 arc second (1”) = 1/60 of an arc min 60’ = 1 degree 1 degree = 3600” Dec = 12 degrees 30’ 15” N 60” = 1’ Right Ascension: 1 hour = 1/24 of sky RA 1 minute = 1/60 hour 12h 30m 15s 12h 31m 15s = 1m 1 second = 1/60 minute 23h 12m 0s 1h 12m 0s = 2h 0m 0s...
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## This note was uploaded on 02/17/2010 for the course PHY 115 taught by Professor Weinbeck during the Spring '09 term at BC.

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Lecture 2 - the North Celestial Pole sweeps a large circle...

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