astronomy 104 lunar phases andeclipses january 24, 2007
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Astronomy 104Astronomy 104
Lunar Phases Lunar Phases
And And
EclipsesEclipses
January 24, 2007January 24, 2007
ReviewReview
ConstellationsConstellations 88 different star clusters88 different star clusters Map out entire celestial sphereMap out entire celestial sphere Used to locate starsUsed to locate stars
Celestial SphereCelestial Sphere North and South Celestial PolesNorth and South Celestial Poles Celestial EquatorCelestial Equator Rotation of Stars around PolesRotation of Stars around Poles Apparent motion of Stars at Poles, Equator and mid-Apparent motion of Stars at Poles, Equator and mid-
latitudeslatitudes
Ecliptic – apparent path of the sun around Ecliptic – apparent path of the sun around the celestial spherethe celestial sphereTilted at 23.5 degrees from celestial equatorTilted at 23.5 degrees from celestial equator
Cause of the SeasonsCause of the SeasonsSummer/Winter Solstice-sun is directly above Summer/Winter Solstice-sun is directly above
the Tropic of Cancer/Capricorn. Sun does not the Tropic of Cancer/Capricorn. Sun does not set/rise above arctic circle set/rise above arctic circle
Vernal/Autumnal Solstice – sun crosses the Vernal/Autumnal Solstice – sun crosses the celestial equator – sun directly above equator.celestial equator – sun directly above equator.
ReviewReview
Celestial Sphere MeasurementsCelestial Sphere Measurements
Zenith: Point directly Zenith: Point directly above the observer.above the observer.
Meridian: Line from Meridian: Line from North Pole to South North Pole to South Pole that passes Pole that passes through the Zeniththrough the Zenith Morning: Ante MeridianMorning: Ante Meridian Afternoon: Post MeridianAfternoon: Post Meridian
Horizon: Circle around Horizon: Circle around observer where sky and observer where sky and ground appear to meet.ground appear to meet.
Vernal EquinoxVernal Equinox
Point on the Point on the Celestial Celestial Sphere Sphere directly directly behind the behind the sun during sun during the First day the First day of Spring of Spring (March 21).(March 21).
Celestial CoordinatesCelestial Coordinates Angle of Right Ascension: Angle of Right Ascension:
Measured in Hours, Min, Measured in Hours, Min, Sec.Sec.
If Vernal Equinox at If Vernal Equinox at midnight is at Zenith, then midnight is at Zenith, then the Angle of Right the Angle of Right ascension is the time at ascension is the time at which the star of interest which the star of interest is at Zenith. is at Zenith.
Angle of declination is the Angle of declination is the angle toward the north angle toward the north pole the object is from pole the object is from Zenith.Zenith.
Example:Example:
We want to locate the star Vega. It’s We want to locate the star Vega. It’s coordinates are coordinates are
RA: 18h 36m 56.3s RA: 18h 36m 56.3s
Dec: +38° 47' 01“Dec: +38° 47' 01“Locate Vernal Equinox: Move 18 h 36 m Locate Vernal Equinox: Move 18 h 36 m
56.3s east. Move 38° 47' 01“ toward the 56.3s east. Move 38° 47' 01“ toward the north. north.
Sidereal vs Solar DaySidereal vs Solar Day
Solar Day: Time for sun to move from Solar Day: Time for sun to move from Meridian back to Meridian = 24 hours.Meridian back to Meridian = 24 hours.
Sidereal Day: Time for any star on the Sidereal Day: Time for any star on the celestial sphere to move from Meridian celestial sphere to move from Meridian back to Meridian = 23 hours 56 minutesback to Meridian = 23 hours 56 minutes
Difference due to motion of earth around Difference due to motion of earth around the sun.the sun.
Lunar ObservationsLunar Observations
When you watched the moon at night this past When you watched the moon at night this past week, what observations did you make?week, what observations did you make?
Common ObservationsCommon Observations
The moon passes through phases, The moon passes through phases, changing slightly every night.changing slightly every night.
The time at which the moon rises changes The time at which the moon rises changes by about one hour every night.by about one hour every night.
The surface of the moon is made of light The surface of the moon is made of light and dark regions. These regions do not and dark regions. These regions do not change with time.change with time.
Lunar PhasesLunar Phases
The side of the moon that faces the sun is The side of the moon that faces the sun is bright.bright.
The side of the moon that faces away from The side of the moon that faces away from the sun is dark.the sun is dark.
Where the moon is in its orbit determines Where the moon is in its orbit determines what portion of the light and dark sides we what portion of the light and dark sides we see.see.
Lunar PhasesLunar Phases
New MoonNew Moon – we see only dark side. – we see only dark side.Moon is between Earth and sunMoon is between Earth and sunMoon rises at sunrise, sets at sunset.Moon rises at sunrise, sets at sunset.
Waxing CrescentWaxing Crescent First Quarter-First Quarter- we see half light /half dark we see half light /half dark
Moon is at right angles with sunMoon is at right angles with sunMoon rises at Noon, sets at Midnight.Moon rises at Noon, sets at Midnight.
Waxing GibbousWaxing Gibbous
Full MoonFull Moon – we only see bright side – we only see bright sideMoon is directly opposite the sunMoon is directly opposite the sunMoon rises at sunset and sets at sunriseMoon rises at sunset and sets at sunrise
Waning GibbousWaning GibbousThird (Last) QuarterThird (Last) Quarter – we see half – we see half
bright/half darkbright/half darkMoon is at right angles wit hthe sunMoon is at right angles wit hthe sunMoon rises at midnight and sets at noonMoon rises at midnight and sets at noon
Waning CrescentWaning Crescent
Lunar PhasesLunar Phases
Lunar MonthLunar Month
Sidereal Month – Time for the moon to Sidereal Month – Time for the moon to return to its same position in the sky return to its same position in the sky relative to a particular constellationrelative to a particular constellation= 27.32 days= 27.32 days
Synodic Month – Time for the moon to Synodic Month – Time for the moon to return to its same position relative to the return to its same position relative to the sun, (e.g. from Full Moon to Full Moon) sun, (e.g. from Full Moon to Full Moon) = 29.53 days= 29.53 days
Rotation of the MoonRotation of the Moon
The rotation of the earth on its axis The rotation of the earth on its axis determines the length of the daydetermines the length of the day
The orbit of the earth around the sun The orbit of the earth around the sun determines the length of the yeardetermines the length of the year
The orbit of the moon around the earth The orbit of the moon around the earth determines the length of the lunar month.determines the length of the lunar month.
What is the length of a day on the moon?What is the length of a day on the moon?
Rotation of the MoonRotation of the Moon
When we look at the moon, we always see the When we look at the moon, we always see the same side. - “The Man in the Moon”same side. - “The Man in the Moon”
Suppose you landed on the moon in the “Sea of Suppose you landed on the moon in the “Sea of Tranquility” (a dark area of the moon on the side Tranquility” (a dark area of the moon on the side facing the earth) during a full moon.facing the earth) during a full moon. Where would you observe the sun?Where would you observe the sun? Seven days later where would you observe the sun?Seven days later where would you observe the sun? Fourteen days? Twenty-one days?, Twenty-eight Fourteen days? Twenty-one days?, Twenty-eight
days?days?
Lunar EclipseLunar Eclipse
Moon passes through Earth’s shadowMoon passes through Earth’s shadowOnly occurs during Full Moon Only occurs during Full Moon Only occurs when moon is on Line of NodesOnly occurs when moon is on Line of Nodes
Solar EclipseSolar Eclipse
Earth passes through Moon’s ShadowEarth passes through Moon’s ShadowOnly occurs during New MoonOnly occurs during New MoonOnly occurs when Moon is on Line of Nodes Only occurs when Moon is on Line of Nodes Since Moon is much smaller than Earth, only Since Moon is much smaller than Earth, only
a portion of the Earth Experiences the a portion of the Earth Experiences the EclipseEclipse