nearby constellations
DESCRIPTION
Nearby Constellations. (2-D “Constellations”, from Stars in 3-D !). 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 ” - PowerPoint PPT PresentationTRANSCRIPT
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.)
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” (d) 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 365.2425 Days 365.25 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 365.25 Solar Days
366.25 Sidereal Days
“Precession” of Earth’s Axis,and the temporary nature of the “North Star” . . .
. . . and the “Vernal Equinox”!