Earth, Moon, and SunChapter 19

Earth in Space 19-1

• Astronomy study of objects beyond the Earth’s atmosphere.

• One of the oldest sciences

• Ancient people studied the heavens for agricultural and religious reasons.

Day and Night: Rotation

• Earth spins on its axis (imaginary line that passes through the center of the planet and both poles)

Day and Night: Rotation

• Reason ancient people thought that the sun, moon, and stars were moving around the Earth.

• Causes day and night• Side with light= day• Side without light?• 1 Rotation= 24 hours• 1600km/hour towards

East

Axis

• The axis is currently pointing toward the star Polaris, the North Star

• In 14,000 years the axis will point to Vega due to precession

• Precession- the slight wobble of Earth’s axis (discovered around 150 B.C by Hipparchos)

Revolution, Tilt, and Seasons

• Revolution- movement around another object

• Earth revolves around the Sun• Earth’s axis is tilted 23.5 degrees• Tilt causes seasons

Revolution, Tilt, and Seasons

• Hours of Sunlight• Longer

days/Shorter nights during summer

• Shorter days/ longer nights during winter

• Direct sunlight• Has more energy

• Is hotter

• Hits “beltline”

How long does a revolution take?

Tilt

• The tilt is always towards the North Star, so part of the year the north axis is pointed towards the sun, and part of the year it is pointed away.

Solstices

• Sun is directly at 23.5° north or south latitude.

• Summer (June 21) solstice is the longest day in the Northern Hemisphere.

• The winter solstice (December 21) is the shortest day in the Northern Hemisphere.

• Of course these are reversed if you live in Australia!

Equinoxes

• Means “equal night” (days and nights are equal in time)

• Vernal equinox (spring) occurs around March 21st.

• Autumnal equinox occurs around September 23rd.

• Again if you lived in the Southern Hemisphere these would be reversed!

Prepare

1. Which area of Earth receives the most sunlight?

2. Which receives the least?

3. Why (for both Questions 1 and 2)?

4. Does it change throughout the year?

5. Why (for Question 4)?