Earth Motions and Astronomy Review

What is the shape of Earth?

Oblate spheroid

What is Earth’s circumference at the equator?

40,076 km

What is Earth’s diameter at the equator?

12,756 km

What evidence proves Earth’s shape?

Polaris altitude, gravity differences, photos from space, lunar eclipses, ships disappearing

What is altitude?

Angle measured above the horizon

What is the best evidence of Earth’s shape?

Photographs from space

What is the altitude of Polaris equal to?

Observer’s latitude

What tool measures altitude?

Astrolabe

What is the celestial hemisphere?

Dome of the night sky above Earth

What is altitude in the altitude/azimuth system?

Degrees above the horizon

What is azimuth?

Degrees measured clockwise from north

What is the zenith?

Point directly overhead

What direction is Polaris found?

Due north

How fast do celestial objects appear to move?

15° per hour

Why do stars appear to move east to west?

Earth’s rotation

What are circumpolar stars?

Stars that never set below the horizon

What causes the apparent motion of celestial objects?

Earth’s rotation

What is the best evidence of Earth’s rotation?

Foucault pendulum

How long is one Earth rotation?

23 hr 56 min 4 sec

In what direction does Earth rotate?

West to east

What is the Coriolis Effect?

Deflection of moving objects due to Earth’s rotation

Coriolis deflection in Northern Hemisphere?

To the right

Coriolis deflection in Southern Hemisphere?

To the left

What causes Earth’s seasons?

Revolution, tilt, and parallelism

Earth’s axis is tilted how many degrees?

23.5°

What is Earth’s revolution?

Earth orbiting the Sun

Length of one revolution?

365.26 days

First day of summer in Northern Hemisphere?

June 21

First day of winter?

December 21

What is an equinox?

Equal daylight and darkness

When do equinoxes occur?

March 21 and Sept. 21–23

Where is the Sun directly overhead on June 21?

Tropic of Cancer (23.5°N)

Where is the Sun directly overhead on Dec. 21?

Tropic of Capricorn (23.5°S)

Where is the Sun directly overhead on equinoxes?

Equator

What is solar noon?

When the Sun reaches highest altitude

What is a sidereal day?

23 hr 56 min 4 sec

What is a mean solar day?

Average 24-hour day

What shape are planetary orbits?

Elliptical

What is eccentricity?

Measure of orbit’s oval shape

Formula for eccentricity?

e = distance between foci ÷ major axis

What is perihelion?

Earth closest to Sun

When is perihelion?

Jan. 3–4

Orbital velocity at perihelion?

Fastest

What is aphelion?

Earth farthest from Sun

When is aphelion?

July 3–4

Orbital velocity at aphelion?

Slowest

Kepler’s 1st Law

Planets orbit in ellipses

Kepler’s 2nd Law

Equal areas swept in equal time

Kepler’s 3rd Law

Farther planets have longer periods

Newton’s Law of Gravity

Gravity depends on mass and distance

As mass increases, gravity…

Increases

As distance increases, gravity…

Decreases

Moon revolution period

27.3 days

Moon rotation period

27.3 days

Why do we only see one side of the Moon?

Rotation = revolution

What is a synodic month?

29.5 days

What is perigee?

Moon closest to Earth

What is apogee?

Moon farthest from Earth

What causes Moon phases?

Reflected sunlight

What phase is completely dark?

New Moon

What phase is fully lit?

Full Moon

Waxing means what?

Light increasing

Waning means what?

Light decreasing

What causes tides?

Gravity of Moon and Sun

What are spring tides?

Greatest tidal range

When do spring tides occur?

Full & New Moon

What are neap tides?

Smallest tidal range

When do neap tides occur?

1st & 3rd quarter moons

What is a solar eclipse?

Moon blocks Sun

What phase occurs during solar eclipse?

New Moon

What is a lunar eclipse?

Moon moves into Earth’s shadow

What phase occurs during lunar eclipse?

Full Moon

What is the geocentric model?

Earth-centered model

What is the heliocentric model?

Sun-centered model

What is retrograde motion?

Apparent backward motion of planets

What is an AU?

Average Earth-Sun distance

1 AU equals?

149.6 million km

What elements make up most of the Sun?

Hydrogen and helium

What powers the Sun?

Nuclear fusion

What are terrestrial planets?

Rocky inner planets

What are Jovian planets?

Gas giants

What is the asteroid belt?

Region between Mars and Jupiter

What is a comet tail direction?

Away from the Sun

What is a meteor?

Streak of light in atmosphere

What is a meteorite?

Object that hits Earth

What is a nebula?

Cloud of gas and dust

What is nucleosynthesis?

Formation of heavier elements

What is a protostar?

Early forming star

What is a red giant?

Expanding dying star

What is a white dwarf?

Small hot stellar remnant

What is a supernova?

Explosion of massive star

What is a neutron star?

Dense stellar core

What is a black hole?

Gravity so strong light cannot escape

What does H-R Diagram compare?

Temperature and luminosity

What color are hottest stars?

Blue

What color are coolest stars?

Red

What is the main sequence?

Normal star life stage

What is luminosity?

Brightness compared to Sun

What is the ecliptic?

Sun’s apparent path

What is a light year?

Distance light travels in 1 year