The Suns Motion in the Sky

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The Suns Motion in the Sky
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Where does sunset occur in December?
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The Setting Sun The Sun doesnt like to set
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Map and Unwrap the region on the Celestial sphere
where the Sun travels
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This does to the Celestial Sphere what a Mercator
projection does to a globe
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Solstices and Equinoxes mark the beginnings of
their seasons
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Get out your SFA starchartsPlace the two
rectangular charts side by side

• Locate the Celestial Equator
• Locate the Ecliptic
• The dates written along the Ecliptic show the
  apparent location of the Sun throughout the year.

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• Ecliptic The Path the Sun Travels
• Zodiac The Constellations the Sun Travels
  Through

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What constellation is the Sun in on July 2nd?

• A. Ursa Major
• B. Gemini
• C. Scorpius
• D. Leo

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The Solstices and Equinoxes are both

• Specific points on the celestial sphere.
• Specific instants during the year when the Sun is
  exactly at those points.

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• Solstice Sun Stops compare Armistice
• Equinox Equal night and day (12 hours each)

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Ecliptic (in red) on Celestial Sphere
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What time of day is it?1.Morn, 2.Noon, 3.Eve,
4.Night
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What is the season?1 Sum., 2Fall, 3Win.,
4Spr.
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• There are 365 days in a year ? Sun travels just
  about 1 degree per day against the celestial
  sphere.
• In the course of 1 year, the sun makes 1 fewer
  revolution than the stars do.

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24 hours x 365/366 23 hours and 56 minutes

• 24 hours is a solar day
• 23 hours 56 minutes is a sidereal day

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The Seasons

• The sun goes around the celestial sphere in 1
  year. This means the seasons are connected to
  where the sun is on the celestial sphere.

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Summer Solstice (June 20)(line shows daily path
of Sun)
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At the Spring and Fall Equinoxes(March 20 and
September 20)
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Winter Solstice(December 21)
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THE MOTION OF THE SUN ALONG THE ECLIPTIC CAUSES
THE SEASONS!

• Two effects
• In winter, the sun is above the horizon for a
  smaller fraction of the day
• In winter, even when it is up, the sun hits the
  ground at a lower angle angle.

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Note that in winter same amount of light is
spread out over greater area
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Note with overhead projectorEnergy is more
concentrated when same amount of light falls on a
smaller area.
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What causes winter to be coolerthan summer?

• A. The earth is closer to the Sun in summer than
  in winter
• B. The daylight period is longer in summer
• C. The Sun gets higher in the sky in summer
• D. Both B and C
• E. All of the above

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Practical Application in Architecture
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The Suns Motion viewed from the Equator or the
Pole

• Tropics Anywhere you can stand on the Earths
  surface and have the Sun directly overhead (i.e.
  not Wisconsin).
• Arctic and Antarctic Circles If you are
  anywhere closer to the pole, the Sun will not
  rise at least one day of the year.

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Person Standing at the Pole
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Why are some years leap years?
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Year time for Sun to return to the same spot on
the ecliptic

• Roughly 365.25 days long.
• If you didnt add a leap year, time of spring
  equinox would drift by 1 day every four years.
  In 120 years, all the months would be 1 month
  earlier (e.g. May would occur in what we call
  April)

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• Even leap year system is not perfect Year is
  actually 365.242 189 67 days long
• Gregorian Calendar reform
• Thursday, 4 October 1582 was followed by Friday,
  15 October 1582 in many Catholic countries.
• Century years (e.g. 1900) are not leap years
  unless they are evenly divisible by 400 (e.g.
  2000)

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• William III of England arrived at Brixham in
  England on 5 November (Julian calendar), after
  setting sail from the Netherlands on 11 November
  (Gregorian calendar).
• Shakespeare and Cervantes apparently died on
  exactly the same date (23 April 1616), but in
  fact Cervantes predeceased Shakespeare by ten
  days in real time (for dating these events, Spain
  used the Gregorian calendar, but Britain used the
  Julian calendar). 1
• 1Wikipedia Gregorian Calendar

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Planetarium Sun
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Exercise 4 Planisphere -- Sun
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Exercise 5 Hours of the Day around the World
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What constellation is the Sun near on September
22?

• A. Gemini
• B. Virgo
• C. Sagittarius

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How many daylight hours are there on December 21?

• A. 4.5 hours
• B. 7.5 hours
• C. 10 hours
• D. 12 hours
• E. 15 hours

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When does the Sun rise on June 21?

• A. 430 AM
• B. 530 AM
• C. 630 AM
• D. 730 AM
• E. 830 AM

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Suns Motion through the Stars Caused by
Earths motion
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Day of the year tells you exactly where the
earth is on its orbit.
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Ex 6 Earth in Orbit around the Sun Ex 7 The
constellations throughout the year