Stars and Galaxies Test 2 (Chapters 3-5)

Geocentric view

Earth is the center of the solar system.

Heliocentric view

Nicolaus Copernicus: The sun is the center of solar system.

Retrograde motion

The apparent backward movement of Mars as observed from Earth, caused because Earth catches up to Mar’s orbit and overtakes it.

Epicycle

Ptolemy: A small circle on a planet’s larger circle; the planet itself travels in a circle as it rotates around the Earth.

Diurnal motion

Apparent East to West motion of celestial objects across the sky. Happens because Earth rotates on its axis from West to East.

Kepler’s Law #1

The orbit of each planet is an ellipse with the Sun at one focus.

Eccentricity

Distance between two foci divided by the length of the major axis. e = 0 is a circle, and as e increases it becomes more elliptic.

Kepler’s Law #2

Planets sweep equal areas in equal time intervals. Planets move fastest when closest to the sun.

Perigee

Position on the orbit that is closest to the central gravity body (ex. Sun). At this point, the rotating body moves fastest.

Apigee

Position on the orbit that is farthest to the gravity body, At this point, the revolving body is going slowest.

Perihelion

Earth’s closest point to the Sun on its orbit.

Apehelion

Earth’s farthest point to the sun on its orbit.

Kepler’s Law #3

The further away a planet is from the Sun, the more # of years it will take to orbit.

(P_years)² = (A_AU)³

Period

Tine taken by a planet to complete one orbit around the Sun.

Gravity Slingshot/Assist

A spacecraft/space probe exploration technique that makes use of the increase/decrease in satellite’s speed as it moves around a planet. Increase speed at the fastest point in the orbit to increase orbit size, use that to slingshot to the orbit of another planet.

Newton’s Law #1 (Law of Inertia)

Objects at rest remain at rest and objects in motion stay in motion until an external force acts on it.

Inertial frame of reference

A reference frame moving in a straight line at constant speed.

Newton’s Law #2

A net (unbalanced) external force will accelerate an object.

Forces change motion by changing the speed or direction of motion.

Newton’s Law #3

When an object exterts a force on a second object, a matching force will be exerted on the first object by the second object in the opposite directions.

Forces always come in pairs.

Gravity

The mutually attractive force between objects that have mass.

Mass

A measure of the amount of material in an object.

Weight

The gravitational force acting on an object attracted by a planet.

Universal Law of Gravitation

Gravity is proportional to the product of the masses of the objects.

Gravity is inversely proportional to the square of the distance (r).

F = (Gm₁m₂)/r²

Orbits

One body falling around another.

Satellite

The less massive object of two objects orbiting around each other.

Free fall

When you are falling around Earth at the same rate of the shuttle.

Tidal forces

Earth’s oceans’ response to the gravitational pull from the moon.

Tidal buldge

The oceans pointed to the moon and opposite of that point are bigger.

Spring Tides

When the Sun and Moon are aligned and are more extreme than normal (New Moon and Full Moon phases).

Neap Tides

When the Moon, Earth, and Sun are at right angles with each other (First and Third Quarter phase). The Sun and Moon’s pull partially cancel each other out.

Tidal Locking

The synchronization between the Moon’s rotation and orbital period (they are equal).

Roche Limit

The limit at which the self-gravitational force of a body on its surface is equal to the tidal force due to another body. Within this limit, the entering planet gets torn apart.

Speed of Light

300,000 [km/s]

Electromagnetic wave

A wave of combined electricity and magnetism.

Wavelength

Length between crests

Amplitude

Height

Frequency

Number of waves that pass by each second.

Period

Time to complete one cycle

Wavelength to Frequency

Wavelength is inversely proportional to frequency

Visible spectrum

Small range of wavelengths that humans can se.

Photon

Particle of light

Energy to frequency

High energy = high frequency

Bohr Model

Electrons that orbit around the nucleus in defined paths.

Quantum Mechanical model

Electrons move in waves in a defined space called an electron cloud, and are more likely to be closer to the nucleus.

Doppler effect

The motion of a light source toward or away from us changes our perception of the wavelength of the waves reaching us. Waves are closer together when the object goes forwards and further spaced apart from behind it.

Blueshifted

Light from approaching objects; the waves crowd together.

Redshifted

The light from receding objects; the waves are spaced farther apart.

Luiminosity

The amount of light leaving a sourcel

Hotter objects = more luminous

Cooler objects = less luminous

Blackbody spectrum

Hotter object: Emits more total light, total energy, and at shorter wavelengths.

Brightness

The amount of light arriving at a particular place.

Brightness is inversely proportional to distance.

Brightness is proportional to luminosity.

Radiation Laws

Accurately predict the temperature of planets without atmospheres.

The farther away a planet, the colder it is.

Inferior Planet

A planet that is closer to the sun than Earth

Superior Planet

A planet that is farther away from the sun than Earth

Synodic Period

The time it takes for a planet to come back to its same position relative to the Sun