Ch. 1 Sec. 1 Earth in Space

astronomy

• study of moon, stars & other objects in space

rotation

Earth spinson its axis 24 hours causes

day & night

imaginary linethat passes

thru Earth’s ctr. & N. & S. Poles

revolution• movement of 1 object around

another

orbit• Earth’s

path as it revolves around Sun

• not round-ellipse (oval)

Earth rotates as it revolves.

Sun

Earth

calendar

• system of organizing time that defines beginning, length & divisions of a year

leap year• 1 year = 365 ¼ days• ¼ + ¼ + ¼ + ¼ = 1 day

leap year every 4 years

1. tilt of Earth’s axis

2. Earth’s revolution

around sun

When the Northern Hemisphere is having summer, Earth is actually at its greatest

distance from the sun.

Near the equator, sunlight strikes Earth’s surface more directly and is less spread out than near the poles.

Earth has seasons because it is tilted as it revolvesaround the sun.

vernalequinox

March 21- noon sun directly over equator

autumnalequinox

Sept. 23- noon sun directly over equator

winter solstice

Dec. 21- shortest day of year-noon sun 23.5 O N

summersolstice

June 21- longest day of year-noon sun 23.5 O S

Seasons in the Northern Hemisphere

equinox

solstice

Equinox means "Equal Night"

1. What causes the Earth's seasons? 2. During which season do the Sun's rays hit the Earth at the most direct angle? 3. During which season are the days the shortest? 4. What is the name and date of the shortest day of the year (and the beginning of winter)? 5. What is the name and date of the longest day of the year (and the beginning of summer)? 6. What is the name of a day in which the day and night are of equal duration? 7. How many times each year do we have days in which the day and night are of equal duration?

Earth’s seasons quiz