Astronomy Lecture Ch 1
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Transcript of Astronomy Lecture Ch 1
Constellations
• A constellation is a section in the sky that contains a group of stars that form a pattern
• The stars even in a constellation are not near each other, they only appear that way from earth
• Stars on average are about 30 trillion miles away from each other
Celestial Sphere
• Is an imaginary sphere with the earth at the center. The poles and equator align with those of the earth.
Angle of Right Ascension
• Abbreviated RA, right ascension is a angular distance measured along the celestial equator.
• The units for RA are hours, minuets, and seconds.
• RA goes from 0 to 24 hours in a easterly direction.
• The starting point (0 h) is at the vernal equinox.
Vernal Equinox
• The vernal equinox is a point where the path of the sun crosses the celestial equator.
• The sun is at the vernal equinox at sunrise on the first day of spring.
Angle of Declination
• Abbreviated DEC, declination is measured north or south or the celestial equator.
• The units for DEC are degrees.
• DEC goes from 0 to 90 degrees.
• The starting point (0◦ ) is located at the celestial equator.
Ecliptic
• The ecliptic is the path the Sun appears to take on the celestial sphere.
• The sun takes one year to complete a cycle around the ecliptic.
Earthly Cycles
• The earth spins around an axis that is goes through its center, north, and south pole.
• The earth moves around the sun in an elliptical orbit.
• There is an angle of 23.5 degrees between the earths axis and the plane that it orbits the sun.
Daily Cycle
• The earth takes 24 hours to complete one rotation around its axis.
• It is this motion that causes the day and night cycles.
• The earth is rotating very fast. A point on the earths equator is moving about 1000 miles per hour.
Yearly Cycle
• The earth takes one year to complete its orbit around the sun.
• The earth is traveling about 67,000 miles per hour.
Earth’s axis precession
• The earth’s axis goes through precession.
• This precession is due to the gravitational pull of the sun and moon.
• One cycle of the precession takes 26,000 years.
The Phases of the Moon
• The moon takes about 29.5 days to go around the earth and go through its phases.
Eclipses
• A lunar eclipse occurs when earth’s shadow blocks the sun’s light to the moon.
• A solar eclipse occurs when the moon blocks the sun’s light to the earth.