Test 10

astronomy

study of God’s creation beyond our atmosphere

perihelion

closest point of an orbit around the sun

aphelion

most distant point of an orbit around the sun

period

the amount of time required for a planet (or other satellite) to complete its orbit

Astronomical units

distance unit approximately equal to the distance between the earth and the sun (150 million km or 93 million mi)

Interplanetary space

space between the planets

vacuum

a space that does not contain any matter

retrograde

rotation of a planet that moves backward, from east to west

Solar system

the sun and all natural objects that orbit it

orbit

to circle around due to gravity; the path of an orbiting object

Aristotle

Greek philosopher who popularized the idea that the universe is geocentric

geocentric

earth centered

Aristarchus

Greek astronomer who proposed that earth orbits the sun

Ptolemy

ancient astronomer from Alexandria, Egypt, who adopted and expanded Aristotle’s geocentric view in his book Almagest

Nicolaus Copernicus

Polish astronomer who proposed the heliocentric theory

heliocentric

sun centered

Galileo

Italian astronomer who built one of the first telescopes and used it in his astronomical investigations

Johannes Kepler

Lutheran astronomer who developed the laws of planetary motion

Tycho Brahe

Danish astronomer whose accurate records helped Kepler prove Copernicus’s ideas

ellipse

symmetrical oval defined so that the sum of the distances from the two foci to a point on the ellipse is constant

Laws of planetary motion

three laws formulated by Johannes Kepler to help explain astronomers’ observations of the planets’ paths

Sir Isaac Newton

scientist who discovered the law of universal gravitation

gravity

force of attraction that exists between any two objects

Law of universal gravitation

law stating that the strength of the gravitational force between two objects depends on their masses and the distance between them

Nebular hypothesis

evolutionary idea that the solar system began forming 4.6 billion years ago when a massive cloud of gas and dust began collapsing inward and rotating, eventually forming the sun and planets

planets

objects that orbit the sun, have enough gravity to be a sphere, and have removed small objects from their orbit

Mercury

closest planet to the sun

Venus

second planet from the sun, which is often the brightest object in the night sky except for the moon

Earth

3rd planet from the sun; the only planet in the solar system that is suitable for life

moon

Earth’s only natural satellite

satellite

any object that orbits a larger object

Lunar month

period of the moon’s elliptical orbit

maria

the moon’s dark patches

rays

streak around a lunar crater that is made up of light-colored powder that was hurled away from the crater when the crater formed

New moon

phase of the moon that occurs when the sunlit side of the moon is turned away from the earth and completely hidden

Waxing crescent

phase of the moon between new moon and first-quarter moon, in which less than half of the moon’s sunlit side is visible from Earth and becoming larger

First-quarter moon

phase of the moon that occurs when half of the moon is visible directly after the waxing crescent phase ends

Waxing gibbous

phase of the moon between first-quarter moon and full moon, in which more than half of the moon’s sunlit side is visible from Earth and becoming larger

Waning gibbous

phase of the moon between full moon and third-quarter moon, in which more than half of the moon’s sunlit side is visible from Earth and is becoming smaller

Third-quarter moon

(also called last-quarter moon) phase of the moon that occurs when only half of the moon is visible directly after the waning gibbous phase

Waning crescent

phase of the moon between third-quarter and new moon, in which less than half of the moon’s sunlit side is visible from Earth and is becoming smaller

Solar eclipse

phenomenon that occurs when a new moon moves directly between the earth and the sun and blocks part or all of the sun from our view

Lunar eclipse

phenomenon that occurs when the full moon passes through the earth’s shadow and the moon darkens because it can no longer reflect the sun’s light

Mars

4^th planet from the sun, known for its reddish-orange color

Olympus Mons

Martian shield volcano that is the largest known mountain in the solar system

Gas giants

any of the planets that are primarily made of gases and are much larger than Earth

Jupiter

5^th planet from the sun; the largest planet in the solar system

Great Red Spot

biggest storm seen on the planet Jupiter

Galilean satellites

four largest moons of Jupiter, which were discovered by Galileo

Saturn

6^th planet from the sun and the second largest planet in the solar system

Uranus

7^th planet from the sun; first planet to be discovered that was not known since ancient times

Neptune

8th planet from the sun; the only planet discovered mathematically before it was seen  

Pluto

solar system object considered the 9^th planet when it was discovered in 1930; now considered a dwarf planet

Eris

trans-Neptunian body larger than Pluto

planet

object that orbits the sun, has enough gravity to be a sphere, and has removed small objects from its orbit

Dwarf planet

object that orbits the sun, has enough gravity to be a sphere, has not removed certain smaller objects from around its orbit, and is not orbiting around another object (besides the sun)

Asteroid

stony or metallic object that is smaller than the planets and orbits the sun

Kuiper belt

belt, similar to the asteroid belt but located outside Neptune's orbit, containing objects that resemble comet nuclei

Celestial sphere

imaginary, giant, hollow sphere with Earth at the center and the sun, moon stars, and other planets on its inner surface

horizon

the line that separates the visible portion of the celestial sphere from the part that we cannot see

Celestial equator

line on the celestial sphere halfway between the celestial poles and directly above Earth’s equator

Circumpolar

refers to stars that are always above the horizon

Ceres

first and largest asteroid discovered (now considered a dwarf planet)

Asteroid belt

large ring of asteroids located between the orbits of Mars and Jupiter

Trojan asteroids

two groups of asteroids that travel in Jupiter’s orbit, one group in front of Jupiter and the other group behind

Near-earth asteroids

(abbreviated NEA) any of a group of asteroids that are located in the inner solar system

comet

asteroid-sized object that is made of rock and frozen materials and forms a bright tail

Edmond Halley

astronomer who correctly calculated the orbit of the comet now known as Halley’s comet

Halley’s comet

comet named after Edmond Halley, who correctly calculated its orbit

nucleus

central structure, such as the ice and dust that forms the heart of a comet, the flattened ball at the center of a spiral galaxy, or the core of an atom

coma

gas and dust cloud around the nucleus of a comet

tail

highly reflective streamer emitted from a comet

Short-period comet

comet that has a period shorter than 200 years

Long-period

comet that has a period longer than 200 years

meteoroid

small chunk of rock or metal in space

meteor

meteoroid that has entered earth’s atmosphere

Meteor shower

phenomenon that occurs when the earth passes through a meteoroid stream and meteors fall much faster than normal

fireball

extremely bright meteor that can be observed over a much larger portion of the earth than an ordinary meteor