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Nearby Constellations. (2-D “Constellations”, from Stars in 3-D !)

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Presentation on theme: "Nearby Constellations. (2-D “Constellations”, from Stars in 3-D !)"— Presentation transcript:

1 Nearby Constellations

2 (2-D “Constellations”, from Stars in 3-D !)

3 This several-hour-long time exposure, taken from tropical northern Australia, shows the clockwise motion of the southern stars around the South Celestial Pole. (Photo by David Miller/DMI.)David Miller/DMI Half-hour time exposure facing north & west. The stars are tracing counter-clockwise circles, centered on a point near the prominent North Star (Polaris). Notice the Big Dipper at the lower-left. “Circumpolar” Stars/Constellations

4 Earth shown at the center of the imaginary “Celestial Sphere”

5 Celestial coordinates: “Declination” (  ) and “Right Ascension” (R.A.) (=> “latitude” & “longitude”!)

6 The Sun’s apparent path through the Celestial Sphere... (actually due to Earth’s annual orbit about the Sun!)

7 “Summer Constellations” vs. “Winter Constellations”, due to Earth’s annual revolution about the Sun:

8 Earth, Sun, and the “Zodiac Constellations” through the Seasons “Summer Signs” = “Winter Constellations”; “Winter Signs” = “Summer Constellations”

9 An Earth-bound Observer sees only half the sky at any one time!

10 “Time Zones” (artificial!), & some famous Meridians around the globe:

11 “Northern” vs. “Southern” Celestial Hemispheres (& Northern/Southern Constellations!) (In Northern Winter/ Southern Summer…) =>

12 What causes the Seasons?

13 Seasonal observations Above is for a Northern Hemisphere location (“Summer” = Higher Sun and Longer Daytimes!)

14 “Land of the Midnight Sun”? (Or the Noon Darkness…?)

15 A good view from Stonehenge! (Sunrise on the Summer Solstice)

16 Ancient “Observatories” in the Americas! (Serving as “Calendars” & “Almanacs”…)

17 The Sun’s apparent path through the Celestial Sphere goes along the “Ecliptic Plane”… TILTED by ~23.5  with respect to Earth’s Rotation (NP/SP) Axis!

18 More Tilt with respect to the Sun => Stronger Seasons!

19 1 Year  365.2425 Days  365.25 Days Christopher Clavius Pope Gregory XIII The lunar crater Clavius, with peripheral craters (Need “Leap Day” Corrections!)

20 “Solar Days” (= a day “by the Sun”) (= 24 hrs.) vs. “Sidereal Days” (= a day “by the Stars”) (= 23 hrs., 56 min.) => 1 Year  365.25 Solar Days  366.25 Sidereal Days

21 “Precession” of Earth’s Axis, and the temporary nature of the “North Star”...... and the “Vernal Equinox”!

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