Nearby Constellations

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

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

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

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

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

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

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

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

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

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

What causes the Seasons?

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

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

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

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

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!

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

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

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

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