AST101 Term Test 1

Astronomical Unit (AU)

The distance from Earth to the sun

1 AU = 1.5 × 10⁸ km

Light-year (ly)

The distance light travels in one year

1 yr = 9.5 × 10¹² km

Mega-years

1,000,000 years = 10⁶ years

Giga-years

10⁹ years

Distance

= speed x time

Arcminutes (‘)

60’ = 1 degree

Arcseconds (“)

60” = 1’

3600” = 1 degree

Angular size

The angle it appears to span in your field of view

Inner solar system planets

Mercury, Venus, Earth, Mars

Outer Solar System planets

Jupiter, Saturn, Uranus, Neptune

Terrestrial Planet

Earth-like

Composed of mainly rock/heavy elements

Small in size

Thin to no atmosphere

Few moons

Jovian (Gas giant) planets

Jupiter-like

Composed of gas and liquid with a small rocky core

Mainly light elements like H/He

Large

Many moons

Rings

Latitude

Measures distance north or south of the equator (0 degrees at equator)

Longitude

Measures distance east or west of an arbitrarily chosen reference point

Greenwich is arbitrary point

Celestial equator

a projection of Earth’s equator into space

The ecliptic sphere

sun’s apparent annual path around the celestial sphere

Plane of the orbit of the planets around the sun

Earth’s is tilted 23.5 degrees

Altitude

Angular height of object above ground

Altitude = latitude

Azimuth

Angular direction of object East to North

Zenith

Straight up (altitude = 90 degrees)

Horizon

Where the sky meets the ground (altitude = 0 degrees)

Circumpolar

Stars never set below the horizon

Milankovitch cycles

1. Eccentricity

2. Obliquity

3. Orbital Precession

Waxing moons

New to full moon

Waning moon

Full to new moon

Lunar Eclipse

moon passes through Earth’s shadow

Happen during FULL moon

Total Lunar Eclipse

Moon passes entirely through umbra

Partial Lunar Eclipse

Part of moon passes through umbra

Part of moon passes through penumbra

Penumbral lunar eclipse

Moon passes through penumbra

Total solar eclipse

Occurs in the small central region (moons umbra)

Partial solar eclipse

occurs in the lighter area (penumbra) surrounding the area of totality

Annular eclipse

When moon’s umbral shadow does not reach earth

Occurs in small central region

Umbra

all sunlight is blocked out

Penumbra

Some of the sunlight is blocked out

Retrograde motion

Object appears to move “backwards” relative to the background

Kepler’s 1st law

The orbit of each planet around the sun is an ellipse with the sun at one focuse

Eccentricity

How circular an ellipse is

Kepler’s 2nd law

As a planet moves around its orbit, it sweeps out equal areas in equal times

Kepler’s third law

More distant planets orbit the sun at slower average speeds

p² = a³

Newton’s Laws of motion and gravity

1. An object will remain at a constant velocity unless acted upon by a net force

2. Net force = mass x acceleration (F=ma)

3. Every force causes an “equal and opposite” reaction force

Mass

the amount of matter in an object

express in kg, g, etc

Weight

The force that an object experiences

lbs, N, etc

Free-fall

If the only force on an object is gravity

Momentum

Mass x velocity

Angular momentum

Radius x mass x velocity

Torque

Force applied at some radius perpendicular to the rotation axis

Kinetic energy

Based on motion (thermal energy)

K = ½ Mv²

Potential energy

Stored energy (gravitational potential energy)

Total mechanical energy

The sum of the kinetic and gravitational potential energy

Spring tides

Occur at new and full moons

Tidal forces from moon and sun add together

Neap tides

Occurs at first and third quarter moon

Tidal forces partially cancel out

Sun and moon perpendicular

Wavelength

The distance from one peak to the next

Frequency

the number of ties each second that electric field vibrates up and down

Thermal radiation

Matter produces light which is temperature dependent

Spectrum

Plot showing how much light is emitted at each wavelength

Thermal Emission laws

1. A hotter object emits more light per unit surface area than a cooler object, at all wavelengths

2. The peak wavelength is shorter for hotter objects, and longer for cooler objects

Doppler effect

The change in the frequency of a wave in relation to an observer who is moving relative to the source of the wave