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Astronomy 104

Astronomy 104. Lunar Phases And Eclipses January 24, 2007. Review. Constellations 88 different star clusters Map out entire celestial sphere Used to locate stars Celestial Sphere North and South Celestial Poles Celestial Equator Rotation of Stars around Poles

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Astronomy 104

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  1. Astronomy 104 Lunar Phases And Eclipses January 24, 2007

  2. Review • Constellations • 88 different star clusters • Map out entire celestial sphere • Used to locate stars • Celestial Sphere • North and South Celestial Poles • Celestial Equator • Rotation of Stars around Poles • Apparent motion of Stars at Poles, Equator and mid-latitudes

  3. Review • Ecliptic – apparent path of the sun around the celestial sphere • Tilted at 23.5 degrees from celestial equator • Cause of the Seasons • Summer/Winter Solstice-sun is directly above the Tropic of Cancer/Capricorn. Sun does not set/rise above arctic circle • Vernal/Autumnal Solstice – sun crosses the celestial equator – sun directly above equator.

  4. Motion of Sun Around Ecliptic

  5. Celestial Sphere Measurements • Zenith: Point directly above the observer. • Meridian: Line from North Pole to South Pole that passes through the Zenith • Morning: Ante Meridian • Afternoon: Post Meridian • Horizon: Circle around observer where sky and ground appear to meet.

  6. Vernal Equinox • Point on the Celestial Sphere directly behind the sun during the First day of Spring (March 21).

  7. Angle of Right Ascension: Measured in Hours, Min, Sec. If Vernal Equinox at midnight is at Zenith, then the Angle of Right ascension is the time at which the star of interest is at Zenith. Angle of declination is the angle toward the north pole the object is from Zenith. Celestial Coordinates

  8. Example: • We want to locate the star Vega. It’s coordinates are RA: 18h 36m 56.3s Dec: +38° 47' 01“ • Locate Vernal Equinox: Move 18 h 36 m 56.3s east. Move 38° 47' 01“ toward the north.

  9. Sidereal vs Solar Day • Solar Day: Time for sun to move from Meridian back to Meridian = 24 hours. • Sidereal Day: Time for any star on the celestial sphere to move from Meridian back to Meridian = 23 hours 56 minutes • Difference due to motion of earth around the sun.

  10. Lunar Observations When you watched the moon at night this past week, what observations did you make?

  11. Common Observations • The moon passes through phases, changing slightly every night. • The time at which the moon rises changes by about one hour every night. • The surface of the moon is made of light and dark regions. These regions do not change with time.

  12. What Causes the Lunar Phases?

  13. Animation 0303-01

  14. Lunar Phases • The side of the moon that faces the sun is bright. • The side of the moon that faces away from the sun is dark. • Where the moon is in its orbit determines what portion of the light and dark sides we see.

  15. Lunar Phases • New Moon – we see only dark side. • Moon is between Earth and sun • Moon rises at sunrise, sets at sunset. • Waxing Crescent • First Quarter- we see half light /half dark • Moon is at right angles with sun • Moon rises at Noon, sets at Midnight. • Waxing Gibbous

  16. Lunar Phases • Full Moon – we only see bright side • Moon is directly opposite the sun • Moon rises at sunset and sets at sunrise • Waning Gibbous • Third (Last) Quarter – we see half bright/half dark • Moon is at right angles wit hthe sun • Moon rises at midnight and sets at noon • Waning Crescent

  17. Lunar Month • Sidereal Month – Time for the moon to return to its same position in the sky relative to a particular constellation= 27.32 days • Synodic Month – Time for the moon to return to its same position relative to the sun, (e.g. from Full Moon to Full Moon) = 29.53 days

  18. Play Animation 03030-03

  19. Rotation of the Moon • The rotation of the earth on its axis determines the length of the day • The orbit of the earth around the sun determines the length of the year • The orbit of the moon around the earth determines the length of the lunar month. • What is the length of a day on the moon?

  20. Rotation of the Moon • When we look at the moon, we always see the same side. - “The Man in the Moon” • Suppose you landed on the moon in the “Sea of Tranquility” (a dark area of the moon on the side facing the earth) during a full moon. • Where would you observe the sun? • Seven days later where would you observe the sun? • Fourteen days? Twenty-one days?, Twenty-eight days?

  21. Play Animation 03030-02

  22. Tilt of Moon’s orbit

  23. Lunar Eclipse • Moon passes through Earth’s shadow • Only occurs during Full Moon • Only occurs when moon is on Line of Nodes

  24. Solar Eclipse • Earth passes through Moon’s Shadow • Only occurs during New Moon • Only occurs when Moon is on Line of Nodes • Since Moon is much smaller than Earth, only a portion of the Earth Experiences the Eclipse

  25. Play Animation 03030-04

  26. http://sunearth.gsfc.nasa.gov/eclipse/eclipse.html

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