The Earth as an Observatory

Why is the sky blue?

• High - above the clouds• Remote mountains or islands – less light pollution

Eratosthene’s Experiment

Eratosthene’s Experiment

How do we know the Earth is spherical?

• sphere• oblate

spheroid• geoid

12,756.27 km

12,713.56 km

2.25” ±0.005 =0.0022%

43.71÷12756.27=0.00037%

Instant Infographics

• Equator• Tropics• Latitude• Longitude• Pole• Horizon• Meridian• Zenith

Refracting Telescopes

• Yerkes ObservatoryWisconsin

• 40” = 100cm

• Van Allen Belts• 1000-60 000km• Solar wind• Protons• Electrons• Endanger

electrics