1. The Cycles of the Sky

2. Celestial Sphere Imaginary dome/sphere surrounding the Earth
Horizon – where the sky meets the ground
Serves as a simplified model for the placement of stars and planets
Stars all appear to be the same distance, but ARE NOT

3. Constellations Fixed patterns of stars
Ancients made pictures of the patterns and related them to certain events of different seasons
Sun in Pisces & Aquarius = dangerous sailing
Sun in Virgo = harvest time
Ex. Big Dipper, Little Dipper, Orion

4. Celestial Poles 2 points of sphere that do not move
Lie directly above the North & South Poles
Polaris (North Star) lies very near North Pole
Used for navigation because it doesn’t move
Stars move from east to west (think Sun)
Ancients thought the celestial sphere was turning
Actually caused by the Earth’s rotation (spinning)
Move counterclockwise around the Celestial poles

5. Celestial Equator Lies above the Earth’s equator
Here stars move due east to due west
Northern hemisphere – stars move northeast to northwest
Southern hemisphere – stars move southeast to southwest
Some stars are far enough north/south that they can not be seen in the other hemisphere
North Star, Southern Cross

8. Annual Motion of Sun (yearly cycle)
Constellations change with the seasons due to the Earth moving (revolving) around the Sun
Any stars in the celestial sphere toward the Sun are blocked by its glare
Ancients used appearance of certain stars/constellations to order their lives
Ex. Sirius near Sun told Egyptians the Nile would be rising
Ex. Same stars are always present when it’s time to plant crops – They didn’t rely on weather, it can be tricky

9. Ecliptic The line the sun traces on the celestial sphere
It passes through 12 constellations called the zodiac
Greek zoidion = “little animal”; kyklos = “circle”
Aries (ram), Taurus (bull), Gemini (twins), Cancer (crab), Leo (lion), Virgo (maiden), Libra (scales), Scorpion, Sagittarius (archer), Capricornus (seagoat), Aquarius (water bearer), Pisces (fish)

11. Seasons - Cause
Earth spins on its Rotational axis – imaginary line from N to S pole
Axis isn’t perpendicular (90) to sun
Tipped 23.5 from vertical
Tilt remains constant throughout Earth’s revolution
Portion tilted toward sun receives more direct light and more hours of light
Seasons are opposite in Northern & Southern Hemispheres

12. Seasons – Ecliptic Tilt
The celestial equator and the sun’s ecliptic differ due to the Earth’s tilt
Equinox (“equal night”) – when sun is on the celestial equator
Day & night are equal length
Marks beginning of spring (vernal) & fall (autumnal)
Usually March 20 & September 22
Solstice – sun is at its extreme north/south position & pauses to change direction
Sun lies 23.5 north/south of celestial equator
Marks beginning of summer & winter
Usually June 21 & December 21
Lag of seasons – coldest/warmest is usually 6 weeks after solstice due to time for land/water to change temperature

14. Seasons – Sun’s Position
Zenith – point directly overhead
Ancients built structures/temples that aligned w/ Sun’s movement
From winter to summer solstice – sun travels north; from summer to winter solstice – sun travels south
Causes a change in sunrise & sunset

15. Seasons – Sun’s Position
At a North latitude of 40
To determine how far above horizon
At summer solstice
= 16.5 away from zenith
= 73.5 above horizon
At winter solstice
= 63.5 away from zenith
= 26.5 above horizon
At equinox
90-40 = 50 above horizon

16. Moon – Lunar Phases Caused by Moon’s orbital motion around Earth
About 29 ½ days – origin of “month”
½ of Moon is always lit by sun
Phase is caused by our position compared to the Moon’s position with the Sun

17. Moon – Lunar Phases New Moon – btw us and Sun
We can’t see the lit half
Will rise about sunrise (6am) & set about sunset (6pm)
Waxing Crescent
1st Quarter – seen about 12pm – 12am (noon-midnight)
Waxing Gibbous
Full Moon – we’re btw Sun & Moon
We see all of the lit half
Seen btw sunset (6pm) & sunrise (6am)
Waning Gibbous
3rd Quarter – seen btw 12am – 12pm (midnight-noon)
Waning Crescent

18. Eclipses
Lunar eclipse – Earth moves btw Sun & Moon and shadows the Moon
Solar eclipse – Moon passes btw Sun & Earth and blocks Sun
Annular eclipse – Moon is farther away from Earth & won’t cover entire sun
Partial eclipse (only a portion is covered) vs Full eclipse
Only occur when the Moon’s orbit aligns w/ the Earth’s
It is actually tipped compared to us
Known as eclipse seasons – twice a year