Sky Motions Diurnal Motion Annual Motion DIURNAL MOTION

Sky Motions þ Diurnal Motion ü Annual Motion

DIURNAL MOTION o Daily East / West motion of the sky Due to the Earth’s rotation (15°/hour) [360°/24 hours = 15°/hour] [1° in 4 minutes] o Stars fall into two groups Circumpolar - never rise or set Equatorial

Circumpolar Stars

Equatorial Stars

View from the North Pole

View from the Equator

Coordinate System

Celestial Meridian n Circle going through north and south points on the horizon and the zenith Z

Celestial Meridian n Objects on the Meridian are at their highest point in the sky (transit) n Astronomical noon is when Sun is on the Meridian. ¤Does not mean the Sun is directly overhead. ¤Midnight is when the Sun is on the Meridian below the horizon.

Zenith n n This is a measure of how high above the horizon the star or planet is located. A star on the horizon has an altitude of 0 o while a star directly overhead (this point is called the z http: //astro. unl. edu/naap/motion 2/s tarpaths. html enith) has an altitude of 90 o.

What is the altitude of a star that is exactly halfway between the horizon and the zenith?

Polaris and Altitude n Polaris “north star” ¤ 1 degee from NCP n Altitude of polaris is always equal to the latitude of the observer. ¤Equator 0º altitude = 0º ¤North pole 90º altitude= 90º aka ¤Grosse pointe 42º altitude = 42º Zenith

South pole n Can you see polaris? ¤Nope!

Annual Motion

ANNUAL MOTIONEarth’s revolution o Constellations move westward during the year. ¤Due to Earth’s orbital motion around the Sun ¤Sun appears to moves eastward 1°/day n o Path of the Sun called the ECLIPTIC Ecliptic inclined 23. 5° to Equator ¤Horizon calendar

Horizon Calendar

Sunrises The Sky and. Dome Sunsets Polaris On the day of an summer solstice… S W On the day of an winter solstice… On the day of an equinox… E N

Polaris W S Winter Solstice Vernal or Autumnal Equinox Summer Solstice N E Starting Points for the Sun

Sunrise in Athens

Stonehenge

Earth’s Annual Motion Leo

NCP Celestial Sphere Autumnal Equinox 23. 5° Ecliptic Vernal Equinox SCP Celestial Equator

Sun’s Motion Tool

Inclined Pole causes Seasons Northern Hemisphere Summer N S Northern Hemisphere Winter 23. 5°

Sun’s motion along the Ecliptic Sun’s Motion

“Stars” o Fixed Stars ¤Modern concept of stars ¤Form the Constellations o Planets - traveling or wandering stars ¤ Sun, Moon, Mercury, Venus, Mars, Jupiter, and Saturn o o Meteors - “shooting stars” Comets - “long-haired stars”