Chapter 24, 25: Earth and the Solar System, Stars and Universe

Question 1

axis

Answer 1

the imaginary line between the Earth’s North and South poles

Question 2

orbit

Answer 2

the path of an object as it moves around a larger object

Question 3

hemisphere

Answer 3

half a sphere, the earth can be considered to be made of two hemispheres divided by the equator

Question 4

the equator

Answer 4

an imaginary line drawn round the earth halfway between the north pole and the south pole

Question 5

phases of the moon

Answer 5

teh different ways the moon looks when viewed from the Earth over a period of one month.

Question 6

planet

Answer 6

a large spherical object that orbits the sun without another similar object close to it

Question 7

minor planet

Answer 7

an object which orbits the sun but is not large enough or far enough from another object to be defined as a parent

Question 8

asteroids and meteoroids

Answer 8

lumps of rock which orbit the sun

Question 9

comet

Answer 9

a ball of ice, dust and gas which orbits the sun in a highly elliptical orbit

Question 10

accretion

Answer 10

the coming together of matter under the influence of gravity to form larger bodies

Question 11

accretion disc

Answer 11

a rotating disc of matter formed by accretion

Question 12

eccentricity

Answer 12

a measure of how elliptical an orbit is

Question 13

orbit radius

Answer 13

the average distance of the planet from the sun

Question 14

orbital period

Answer 14

the time taken for a planet to complete one full orbit of the sun

Question 15

stable star

Answer 15

a star that is not collapsing or expanding because the inward force of gravity is balanced by radiation pressure which pushes outwards.

Question 16

plasma

Answer 16

a completely ionised gas in which the temperature is too high for neutral atoms to exist so it consists of electrons and positively charged atomic nuclei.

Question 17

solar mass

Answer 17

equal to the mass of teh sun (2*1030)

Question 18

lightyear

Answer 18

the distance travelled in space by the light in one year (9.5*1015)

Question 19

protostar

Answer 19

a very young star that is still gathering mass from its parent molecular cloud

Question 20

interstellar cloud

Answer 20

a cloud of gas and dust that occupies the space between the stars

Question 21

molecular cloud

Answer 21

a cloud of interstellar gas that consists mostly of molecular hydrogen and is cold and dense enough to collapse to form stars

Question 22

radiation pressure

Answer 22

the outward force due to the high temperature

Question 23

red giant

Answer 23

a star that began with fewer than eight solar masses and is burning helium in its core its shell of hydrogen has expanded and cooled

Question 24

main sequence

Answer 24

a stable star that is burning hydrogen in its core; once it has used up 12% of its hydrogen it goes to the next stage of it’s life.

Question 25

white dwarf

Answer 25

teh final stage of a star that started with fewer than 8 solar masses after all its fuel has been used up

Question 26

planetary nebula

Answer 26

a bubble of gas surrounded a white dwarf star that used to be the outer shell of a red giant from which it had collapsed.

Question 27

red supergiant

Answer 27

Similar red giants form when stars with at least 8 times the mass of the sun out hydrogen fuel in their core but fusion of hydrogen continues in the outer shells.

Question 28

supernova

Answer 28

an exploding star that began life with more than 8 solar masses and has run out of fuel

Question 29

neutron star

Answer 29

a collapsed almost entirely of neutrons which forms when a star with more than 8 solar masses reaches the end of its life.

Question 30

black hole

Answer 30

teh final stage in the life cycle of a star that starts with more than 8 solar masses: it has enough mass left over after exploding as a supernova to collapse to a point when gravity is so strong that not even light can escape.

Question 31

absorption spectrum

Answer 31

dark lines in a spectrum that are produced when light passing through cooler gas is absorbed

Question 32

redshift

Answer 32

an increase in the observed wavelength of electromagnetic radiation (including visible light) from a star or galaxy because it is moving away from us.

Question 33

big bang theory

Answer 33

the universe was created at a single point 13.8 billion years ago and has been expanding and cooling every since

Question 34

hubbles law

Answer 34

distant galaxies are moving away from te earth with a speed v that is proportional to distance s from the earth where H is the Hubble constant (equation)