Vocabulary

Question 1

asteroid belt

Answer 1

The region between the orbits of Mars and Jupiter that contains most of the asteroids in our Solar System.

Question 2

asteroids

Answer 2

Also called minor planet. A primitive rocky or metallic body (planetesimal) that has survived planetary accretion. Asteroids are parent bodies of meteoroids.

Question 3

astrobiology

Answer 3

An interdisciplinary science combining astronomy, biology, chemistry, geology, and physics to study life in the cosmos.

Question 4

astronomy

Answer 4

The scientific study of planets, stars, galaxies, and the universe as a whole.

Question 5

cosmological principle

Answer 5

The (testable) assumption that the same physical laws that apply here and now also apply everywhere and at all times, and that there are no special locations or directions in the universe.

Question 6

dwarf planet

Answer 6

A body with characteristics similar to those of a classical planet except that it has not cleared smaller bodies from the neighboring regions around its orbit. Compare planet (definition 2).

Question 7

hypothesis

Answer 7

A well-considered idea, based on scientific principles and knowledge, that leads to testable predictions.

Question 8

light-year

Answer 8

The distance that light travels in 1 year—about 9 trillion kilometers (km).

Question 9

Local Group

Answer 9

The small group of galaxies that includes the Milky Way and Andromeda galaxies as members.

Question 10

Milky Way Galaxy

Answer 10

The galaxy in which our Sun and Solar System reside.

Question 11

modern physics

Answer 11

Usually, the physical principles, including relativity and quantum mechanics, developed after 1900.

Question 12

Occam’s razor

Answer 12

The principle that the simplest hypothesis is the most likely, named after William of Occam (circa 1285–1349), the medieval English cleric to whom the idea is attributed.

Question 13

physical law

Answer 13

A broad statement that predicts a particular aspect of how the physical universe behaves and that is supported by many empirical tests

Question 14

planet

Answer 14

1. A large body that orbits the Sun or other star that shines only by light reflected from the Sun or star. 2. In the Solar System, a body that orbits the Sun, has sufficient mass for self-gravity to overcome rigid body forces so that it assumes a spherical shape, and has cleared smaller bodies from the neighborhood around its orbit.

Question 15

principle

Answer 15

A general idea or sense about how the universe is that guides us in constructing new scientific theories. Principles can be testable theories.

Question 16

satellite

Answer 16

An object in orbit about a more massive body—for example, a human-made satellite, or a moon of any planet.

Question 17

scientific method

Answer 17

The formal procedure—including hypothesis, prediction, and experiment or observation—used to test (attempt to falsify) the validity of scientific hypotheses and theories.

Question 18

Solar System

Answer 18

The gravitationally bound system made up of the Sun, planets, dwarf planets, moons, asteroids, comets, and Kuiper Belt objects, along with their associated gas and dust.

Question 19

Sun

Answer 19

The star at the center of the Solar System.

Question 20

supercluster

Answer 20

A large conglomeration of galaxy clusters and galaxy groups; typically, more than 100–300 megaparsecs (Mpc) in size and containing tens of thousands to hundreds of thousands of galaxies.

Question 21

theoretical model

Answer 21

A detailed description of the properties of a particular object or system in terms of known physical laws or theories. Often, a computer calculation of predicted properties based on such a description.

Question 22

theory

Answer 22

A well-developed idea or group of ideas that are tied solidly to known physical laws and make testable predictions about the world. A very well-tested theory may be called a physical law, or simply a fact.