Astronomy 101 - Exam 1 Study Terms

Astronomical Unit

the average distance between the sun and the earth

Light year

the distance that light travels in a year

the celestial sphere

An imaginary sphere (dome) that models the projection of objects in the sky

Horizon

Line where the dome meets the earth

Zenith

Top of the dome, above your head.

Ecliptic Tilt

on the celestial sphere and is the apparent path of the sun over the course of the year.

Tropical Year

Based on the seasons

Sidereal year

Based on the earth’s orbit around the sun. (the true year)

Zodiac

the 12 constellations the sun moves through during the year.

Constellation

Bright stars that are grouped together

Eratosthenes

First person to get a fairly accurate determination of the Earth’s diameter.

Hipparchus

Discovered the position in the sky of the north celestial pole had altered over the previous century → precession “slow shift” of Earth’s axis.

Claudius Ptolemy

proposed a model for the solar system to explain retrograde motions of the planets

Epicycles

a small circle whose center moves around the circumference of a larger one.

Geocentric model

earth lays at the center of the universe

Aristotle

proposed geocentric model

Aristarchus of Samos

proposed that planets revolved around the sun but was ignored because of Aristotle’s following

Heliocentric Model

Planets orbit in circles around the sun

Galileo

built and used the telescope

Kepler’s first law ( The law of orbits )

Planet’s move around the sun in elliptical orbits (ellipses): ea. planets orbit about the sun is an ellipse.

Ellipse

Oval shaped path that celestial objects follow as they orbit the sun

Eccentricity

The determination of how oval an ellipse is. → length of the major axis

Kepler’s 2nd law

A planet moves faster when closer to it’s sun and slower when it’s farther

Kepler’s 3rd Law

the farther a planet is from the sun, the longer it’s orbital period.

Major axis

Diameter of the ellipse, stretching from one end to the other.

Semi major axis

Half of the major axis

Isaac newton

Father of the laws of motion

Angular momentum

The spinning power of an object (spinning or moving in a circle) The faster or heavier the more angular momentum.

Gravity

general force of attraction

Gravitational force

attractive forces between masses.

Aphelion

Farthest distance from sun and moves slowly

Perihelion

Closest distance to sun and moves fast

Escape speed

Speed needed to move away from Earth forever

refraction

the bending of light passing through air or water

solar day

earth’s rotation relative to the sun

sidereal day

earth’s rotation relative to distant stars

synchronous rotation:

rotates once on its axis while simultaneously orbiting earth once. → keeps the same face toward earth

sidereal month

time it takes moon to make a full 360 around earth

synodic month

time it takes moon to complete cycle of phases

Giant Impact Theory

proposes that the moon was formed from the debris of a massive collision between earth and another celestial body.

Solar Eclipse

Sun covered by moon

Lunar Eclipse

Moon dimming.

Annular Eclipse

ring of light

Total Solar Eclipse

Sun completely hidden

Penumbra

sun partially visible

umbra

sun completely blocked.

Electromagnetic Radiation

transmission of energy through space

Mechanical Wave

wave that needs a medium to travel through (ie. sound and water waves)

Electromagnetic Wave (EM)

wave that travels through vacuum, without medium (ie. radio, light, microwaves)

Photon

tiny packets of energy that makeup light

Inverse Square Law for Light Propagation

light becomes weaker the further it travels from its source

Electromagnetic Spectrum

range of EM radiation

Blackbody Radiation

type of light emitted by an object and absorbs light

Wien’s law

as an object gets hotter, its peak wavelength become smaller

Stefan-Boltzmann Law

as the temperature of an object increases, it radiates more energy.

Spectrometer

device to measure and analyze the properties of light such wavelength and energy

Atom

building block of all matter

Doppler Effect

wavelength of light shortens toward source, lengthens away from it.

Reflector

telescope using mirrors

Refractor

telescope using lens