The Earth-Moon System Moon Mass 7.3483 x 1022 kg Equatorial Radius 1737.4 km Earth Mass 5.97219 x 1024 kg Mean Radius 6371.00 km

Orbital Parameters Average distance from Earth 384,400 km (0.00257 A.U.) Perigee 363,300 km Eccentricity 0.05490 Orbital Inclination to Ecliptic 5.145 degrees Sidereal Orbit Period 27.321661 Earth days Sidereal Rotation Period 27.321661 Earth days Equatorial Inclination to Orbit 6.68 degrees

Origin of the Moon Likely formed after a Mars-sized body collided with Earth Moon formed out of the debris

Phases of the Moon

Phases Synodic month 29.53 days Sidereal Lunar Orbit 27.32 days Actual period variable – perturbations Moon and Sun both subtend ~0.5 degrees Eclipses – Lunar, Solar Occur when moon curs ecliptic, twice a year Approximately 4 to 7 eclipses per year

Total Solar Eclipse 1999

Tides in Fundy Bay

Different Types of Tides Semidiurnal Mixed Tide Diurnal

Tidal Forces

What causes tides Main constituent Principal Lunar Semidiurnal 12 hr 25 min period Slightly longer than 12 hrs due to Lunar orbit – same direction as Earth’s spin Other effects – Sun’s gravity, inclination of Earth’s spin, moon’s orbit, variation in distances Coastline

Spring and Neap Tides

Roche Limit

Interacting Galaxies NGC 4676: When Mice Collide Credit: ACS Science & Engineering Team, NASA

Whirlpool Galaxy NGC 5194 Credit NASA/ESA