Bringing Astronomy Down to Earth

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Bringing Astronomy Down to Earth

• What do we know about
• Earth Moon Sun interactions?

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Earths rotation

• The Earth rotates on its axis (it makes one
  complete turn) every 24 hours

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Earths rotation is the cause of our day and night
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Which way does the Earth rotate?From west to east
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Earths revolution

• The Earth revolves around the sun (makes one
  complete circuit) once every 365.26 days
• This is the cause of our year

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Leap year

• Every 4 years we add one day to the calendar year
  to make up the 1/4th of a day that we miss each
  year
• The last leap year was 2008, the next will be
  _____.

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Other variations in Earths movement

• Every 100,000 years the Earths elliptical orbit
  varies from more elongated to more circular
• Every 41,000 years the tilt of the Earth on its
  axis varies between 21.50 and 24.50

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Precession every 26,000 yearsthe circular
motion of the Earth on its axis...causes the
Earth to spin like a top on a table

• Right now the axis points towards Polaris (North
  Star)
• In the future will point to the star Vega

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These are called Milankovitch cycles and they are
believed to be one of the causes that the Earths
climate cycles between ice ages and warm periods
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What do we mean by latitude and longitude?

• Latitude Horizontal (N or S)
• Longitude Vertical (E or W)

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Lines of Latitude00 to 900 N, 00 to 900 S
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Important Lines of Latitude
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What is the latitude of Narragansett, RI?
http//www.epodunk.com/cgi-bin/genInfo.php?locInde
x13438
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Aphelion/Perihelion

• Because of the Earths elliptical orbit, the
  distance between the earth and the sun varies
  through the year
• We are closest at perihelion we are furthest
  apart at aphelion (apart/aphelion)

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Aphelion (furthest from sun) occurs on July 4th
(152 million km) and Perihelion (closest to sun)
occurs on January 3rd (147 million km)
Closest in January??? Then why is it coldest???
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What causes the seasons??The tilt of the earth
on its axis!!
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During our summer Northern hemisphere fully
faces the sun During our winter Southern
hemisphere fully faces the sun
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A Summer Solstice June 20 or 21 solstice
means sun stop the sun stops getting higher
in the sky each day The suns rays are directed
at the Tropic of Cancer
B Autumnal Equinox September 22 or 23 Equinox
means equal nights length of day and night are
equal all over the world The suns rays are
directed at the equator
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C Winter Solstice Dec. 21 or 22 sun is
lowest in the skyThe suns rays are directed at
the Tropic of Capricorn
D Spring Equinox March 20 or 21 The suns
rays are directed at the equator
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Daylight Change by Latitude
Can you detect the times of equinox? Can you
detect the summer and winter solstices?
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What is an eclipse?An eclipse occurs when one
planetary body passes through the shadow of
another.Eclipses are named depending on which
body is eclipsed, or blocked
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Solar Eclipse (the sun is eclipsed or
blocked)The moon is between the sun and earth -
the shadow of the moon falls on the earth
Within the umbra, you see a total eclipse
(smaller area in shadow) Within the penumbra, you
see a partial eclipse (larger area in the
shadow) Solar eclipses never last gt 7 minutes at
any location. Why??
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Lunar Eclipse (the moon is eclipsed, or
blocked) The earth is between the moon and the
sun - the earths shadow falls on the lighted
half of the moon
Total lunar eclipse moon must pass entirely
through the earths umbra Partial lunar eclipse
only part of the moon passes through umbra Lunar
eclipses may last hours!!
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The moon looks reddish during a lunar eclipse
because the sunlight reflected off the moon is
bent in the earths atmosphere
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Moon Phases
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Phases of the Moon As Moon revolves around the
Earth, different parts of the lighted side of the
moon face Earth

• New moon moon is between sun and earth no
  visible moon
• Full moon earth is between sun and moon fully
  visible moon
• Crescent moon lt half of moon visible
• Gibbous moon gt half of moon visible
• Waxing visible part is increasing
• Waning visible part is decreasing

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Moon Phases
New moon ? waxing crescent ? first quarter ?
waxing gibbous ? full moon ? waning gibbous ?
last quarter ? waning crescent ? back to new moon
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Phases of the Moon
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Tides daily changes in the level of the ocean
surface

• Caused by the gravitational pull of the moon (and
  the sun) on the Earths waters

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Both Sun and Moon cause the tides
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Spring tides S-E-MNeap Tides S-E
M
Spring tides highest high tides of the month at
times of new and full moons Neap tides lowest
high tides of the month at 1st and last quarters
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Neap and Spring Tides
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Tides 3 tidal patterns

• diurnal tides one high, one low every 24 hours
• semidiurnal tides two equal high, two equal low
  every 24 hours
• semidiurnal mixed tides 2 highs of different
  heights, 2 lows of different heights every 24
  hours

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• Tidal range difference in height between the
  highest high and the lowest low tide
• Tidal period time between one high tide and next
  high tide
• Tidal day time between 1st high tide and last
  high tide in 24 hours

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What kind of tides in Eastport, ME?Look at the
daily tidal range!
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What kind of tides in Grand Isle, LA?Look at the
daily tidal range
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What kind of tides in Crescent City, CA?
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What kind of tides in Newport, RI ?Look at the
daily tidal range