Chapter 10 Earth’s Place in Space

Earth’s Shape Spherical Shaped like a ball

Evidence of Earth’s Shape Horizon Boat coming over horizon (you see the top first) Shadow Curved shadow during lunar eclipse Gravity Gravity attracts particles toward center Pictures Pictures from space

Not Quite a Perfect Sphere… Slight bulge at equator due to spinning (centrifugal force)

What is a “Day”? Rotation Time it takes for Earth to rotate one complete turn = 1 day Each Rotation is one day (24 hours) Why Sun (and moon/stars) rises and sets

What is a “Year”? Revolution (orbit) Each Revolution is one year

Why does Earth orbit the Sun? Gravity The sun’s gravitational pull holds the Earth in orbit Gravitational pull depends on the masses of the objects and the distance between them Earth’s orbit around the Sun is nearly circular Ellipse (with Sun at one focus)

How does the Sun give us energy? Fusion – In the Sun’s core, there is so much heat and pressure that the nuclei of atoms combine. This process releases LARGE amounts of energy. Core temperature = 15,000,000 °C Surface temperature = 5,500 °C Light & Thermal Energy – Some of the Sun’s energy reaches us on Earth as light and heat.

What Causes the Seasons? Earth’s Tilt (23.5⁰) More Direct Sunlight Summer Longer Days Less Direct Sunlight Winter Shorter Days

Solstices and Equinoxes Summer - Sun reaches far point North of Equator Tropic of Cancer Longest Day Winter – Sun reaches far point South of Equator Tropic of Capricorn Shortest Day Equinox Sun Directly above Equator Spring and Fall

Solstices and Equinoxes (p.289)

Earth’s Seasons Indirect Sunlight Direct Sunlight Shorter Days Longer Days