Stars & Stellar Evolution

Question 1

luminosity

Answer 1

the rate at which a star or other object emits electromagnetic energy into space; the total power output of an object

Question 2

apparent brightness

Answer 2

a measure of the amount of light received by Earth from a star or other object—that is, how bright an object appears in the sky, as contrasted with its luminosity

Question 3

magnitude

Answer 3

an older system of measuring the amount of light we receive from a star or other luminous object; the larger the magnitude, the less radiation we receive from the object

Question 4

color index

Answer 4

difference between the magnitudes of a star or other object measured in light of two different spectral regions—for example, blue minus visual (B–V) magnitudes

Question 5

brown dwarf

Answer 5

an object intermediate in size between a planet and a star; the approximate mass range is from about 1/100 of the mass of the Sun up to the lower mass limit for self-sustaining nuclear reactions, which is about 0.075 the mass of the Sun; brown dwarfs are capable of deuterium fusion, but not hydrogen fusion

Question 6

spectral class

Answer 6

(or spectral type) the classification of stars according to their temperatures using the characteristics of their spectra; the types are O, B, A, F, G, K, and M with L, T, and Y added recently for cooler star-like objects that recent survey have revealed

Question 7

giant

Answer 7

a star of exaggerated size with a large, extended photosphere

Question 8

proper motion

Answer 8

the angular change per year in the direction of a star as seen from the Sun

Question 9

radial velocity

Answer 9

motion toward or away from the observer; the component of relative velocity that lies in the line of sight

Question 10

space velocity

Answer 10

the total (three-dimensional) speed and direction with which an object is moving through space relative to the Sun

Question 11

selection effect

Answer 11

the selection of sample data in a nonrandom way, causing the sample data to be unrepresentative of the entire data set

Question 12

eclipsing binary

Answer 12

a binary star in which the plane of revolution of the two stars is nearly edge-on to our line of sight, so that the light of one star is periodically diminished by the other passing in front of it

Question 13

distances Light year=KM=CM

Answer 13

1 light-year = 9.5 × 1012 km = 9.5 × 1017 cm

Question 14

interstellar dust

Answer 14

tiny solid grains in interstellar space thought to consist of a core of rocklike material (silicates) or graphite surrounded by a mantle of ices; water, methane, and ammonia are probably the most abundant ices

Question 15

interstellar medium (ISM)

Answer 15

or interstellar matter) the gas and dust between the stars in a galaxy

Question 16

nebula

Answer 16

a cloud of interstellar gas or dust; the term is most often used for clouds that are seen to glow with visible light or infrared