Astrophysics Terminology SL

Question 1

solar system

Answer 1

collection of planets, moons, asteroids, comets, and other rocky objects in elliptical orbit around the sun

Question 2

asteroids

Answer 2

rocky objects orbiting the sun

Question 3

comets

Answer 3

irregular objects of ice, rock, and dust orbiting the sun

Question 4

nebula

Answer 4

enormous cloud of dust and gas where stars often form

Question 5

binary stars

Answer 5

two stars that rotate about a common center of mass

Question 6

stellar cluster

Answer 6

group of stars close enough to be held together by gravity

Question 7

open cluster

Answer 7

several hundred stars younger than ten billion years that still contain gas and dust

Question 8

global cluster

Answer 8

stars older than 11 billion years containing little gas and dust

Question 9

constellation

Answer 9

pattern formed from stars, not held together by gravity

Question 10

galaxy

Answer 10

stars, gas, and dust held together by gravity containing billions of stars

Question 11

spiral galaxies

Answer 11

disc shape with spiral arms spreading out from a central galactic bulge that contains the greatest density of stars

Question 12

spiral arms

Answer 12

many young blue stars, gas, and dust

Question 13

irregular galaxies

Answer 13

shapeless and can be stretched in the presence of other bigger galaxies

Question 14

light year

Answer 14

distance traveled by light in one year ( 1ly = 9.46 x 10^15 m )

Question 15

astronomical unit

Answer 15

average distance between the sun and earth (au) 1au =1.50 x 10^11m – approximately 8mins

Question 16

parsec

Answer 16

(pc) most commonly used distance in astrophysics 1pc = 3.26 ly = 3.09 x 10^16m

Question 17

stellar parallax

Answer 17

the star’s apparent shift of position of any nearby star against the background of distant stars – which can be used to measure the distance of stars from us

Question 18

luminosity

Answer 18

the energy emitted by the star per second in watts – amount of light emitted from the stars surface

Question 19

brightness

Answer 19

watts per square meter (Wm^-2) – how bright the star appears to be from earth

Question 20

black bodies

Answer 20

theoretical objects that absorb all radiation incident upon them. perfect emitters for radiation, emitting the maximum radiation possible at their temperature

Question 21

black body radiation

Answer 21

all objects with temperatures above absolute zero emits this

Question 22

cepheid variables

Answer 22

highly luminous stars with regular and predictable changes in luminosity due to its cycle

Question 23

What is the cycle of a cepheid star?

Answer 23

1. Layer loses hydrostatic equilibrium and compresses inwards
2. The star becomes less transparent
3. The star heats up and internal pressure increases
4. The layer of the star is pushed outwards, therefore, the star expands
5. The layer cools and becomes less dense
6. The radiation escapes and the pressure inside the star decreases. – The cycle then repeats

Question 24

Hertzsprung-Russell diagram

Answer 24

depicts the relationship between the luminosities and temperatures of the stars (memorize the groups of stars on that diagram)

Question 25

red giant stars

Answer 25

Cooler stars that emit less energy. They have higher luminosities and a larger surface area/diameter compared to the sun

Question 26

Supergiant stars

Answer 26

Gigantic, bright stars that emit more energy with a larger surface area/diameter compared to the sun

Question 27

White dwarfs

Answer 27

Remnants of old stars that are hot and dense. They have low luminosity and a small surface area

Question 28

Main sequence star

Answer 28

Any star that fuses hydrogen in its core and has a stable balance of outward pressure due to nuclear fusion. Gravitational forces push inwards. -- hotter and bigger stars w/ a finite life time

Question 29

hydrostatic equilibrium

Answer 29

pressure due to gravitational attraction of inner shells is equal to the thermal and radiation pressure acting outwards

Question 30

electron degeneracy pressure

Answer 30

resistance a densely patched gas of electrons exerts against further compression -- this prevents the collapse of celestial objects

Question 31

supernova

Answer 31

when a star collapses and the neutrons come close to each other. the outer layers of the star rush toward the core but then explode. the remnants are the neutron stars

Question 32

neutron degeneracy pressure

Answer 32

pressure of a neutron star that resists further gravitational collapse into a black hole

Question 33

Oppenheimer-volkoff limit

Answer 33

the upper value of a neutron star where neutron degeneracy resists further collapse of a black hole

Question 34

black hole

Answer 34

a region of space having a gravitational field so intense that no matter or radiation can escape

Question 35

local redshift

Answer 35

occurs within galaxies or clusters, when movement causes the wavelengths emitted to be longer

Question 36

blue shift

Answer 36

when movement causes the wavelengths emitted to be shorter

Question 37

cosmological redshift

Answer 37

the larger scale of local redshift that is associated with the expansion of the universe. Light travels through the expanding space thus its wavelength is stretched

Question 38

solar mass

Answer 38

standard unit of mass in astronomy -- the approximate mass of the sun ( 2 x 10^30 kg )

Question 39

What is the period-luminosity law for the Cepheid stars?

Answer 39

It's the relationship between the pulsation period of a cepheid star and its luminosity. The brighter the star, the slower it pulses.

Question 40

Chandrasekhar mass limit

Answer 40

Approximately 1.4 times the mass of the sun -- determines whether a star will form a white dwarf or a neutron star If the mass of the remnant core after the red giant phase is < mass limit, it will become a white dwarf If the mass of the remnant core > mass limit, it will become a neutron star or black hole

Question 41

hubble's law

Answer 41

the velocity that galaxies are moving away from us is directly proportional to their distance from us -- the further away the galaxy is, the faster it is moving away