Introduction to Astronomy

How big, and small, is our universe, and how do scientists measure these vast differences?

• Scientific Notation—a convenient way for scientists to measure very large or very small numbers, using exponents, and the power of 10

Astronomical Unit• The average distance between the sun and

earth • 149,597,870,700 meters (about 93 million

miles)• 1 light year equals 6 trillion miles

What do you see when you look at the view of the sky? What is the daily motion of the sun, moon, stars and

other planets?

Phases of the moon

Greeks: Geocentric Model

• The earth is the center of every celestial object’s movement

• Perfect circular orbit• Uniform speed

Copernicus (14-15th century): First to explain a heliocentric model

• Sun is center of planetary motions• Inner planets move faster than outer planets• Uniform circular orbits; constant speeds

Kepler (1571-1630) German

• Planetary orbits are ellipses with the sun at one of the foci

• Equal area vs. equal time orbital speed

Galileo (1564-1642)

• First to observe night sky with a telescope he made

• The moon has “oceans” and mountains• Venus has phases (just like the moon)