Astronomy Unit 4

Question 1

the cycling of mass in and out of the interstellar medium, including accretion of gas from
intergalactic space, loss of gas back into intergalactic space, and conversion of interstellar gas into stars

Answer 1

baryon cycle

Question 2

atomic nuclei (mostly protons) and electrons that are observed to strike Earth’s atmosphere with
exceedingly high energies.

Answer 2

cosmic rays

Question 3

the region of ionized hydrogen in interstellar space

Answer 3

H II region

Question 4

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

Answer 4

interstellar dust

Question 5

the attenuation or absorption of light by dust in the interstellar medium

Answer 5

interstellar extinction

Question 6

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

Answer 6

interstellar medium (ISM)

Question 7

(or Local Hot Bubble) a region of low-density, million degree gas in which the Sun and solar
system are currently located

Answer 7

Local Bubble

Question 8

a slightly denser cloud inside the Local Bubble, inside which the Sun also lies

Answer 8

Local fluff

Question 9

a large, dense, cold interstellar cloud; because of its size and density, this type of cloud can
keep ultraviolet radiation from reaching its interior, where molecules are able to form

Answer 9

molecular cloud

Question 10

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

Answer 10

nebula

Question 11

the reddening of starlight passing through interstellar dust because dust scatters
blue light more effectively than red

Answer 11

reddening (interstellar)

Question 12

a planet orbiting a star other than our Sun

Answer 12

exoplanet

Question 13

large, cold interstellar clouds with diameters of dozens of light-years and typical
masses of 105 solar masses; found in the spiral arms of galaxies, these clouds are where stars form

Answer 13

giant molecular clouds

Question 14

luminous knots of gas in an area of star formation that are set to glow by jets of
material from a protostar

Answer 14

Herbig-Haro (HH) objec

Question 15

a planet that is intermediate between the largest terrestrial planet in our solar system (Earth)
and the smallest jovian planet (Neptune); generally, mini-Neptunes have sizes between 2.8 and 4 times Earth’s
size

Answer 15

mini neptune

Question 16

a very young star still in the process of formation, before nuclear fusion begins

Answer 16

protostar

Question 17

the outflow of gas, sometimes at speeds as high as hundreds of kilometers per second, from a
star

Answer 17

stellar wind

Question 18

a planet larger than Earth, generally between 1.4 and 2.8 times the size of our planet

Answer 18

super-earth

Question 19

when one astronomical object moves in front of another

Answer 19

transit