astrophysics

Question 1

the universe:

Answer 1

-a large collection of billions of galaxies

Question 2

a galaxy:

Answer 2

-a large collection of billions of stars

Question 3

solar system:

Answer 3

-a collection of planets orbiting a common star
-our solar system is in the Milky Way galaxy

Question 4

gravitational field strength: (now that this makes everything orbit)

Answer 4

-> the force per unit mass on a body in a gravitational field
-measured in Newtons per kilogram (N/kg)
-it varies with the mass and size of the body and is different on other planets and the moon compared to earth (on earth: 10 N/kg)
-weight = mass x gravitational field strength W=mg

Question 5

Moons and orbits:

Answer 5

-Moons orbit planets
-The orbits are slightly elliptical with near constant orbital speed

Question 6

Planets and comets:

Answer 6

-Planets and comets orbit the Sun
-the orbits of planets are slightly elliptical with near constant orbital speed
-the orbits of comets are highly elliptical
-made of ice (usually)
-closest to the sun = fastest
-farthest to the sun = slowest

Question 7

artifical satellites:

Answer 7

-artificial satellites (human made) orbit the earth
-the greater the orbital radius the smaller the time period, the greater orbital speed
-orbital speed = 2 x π x orbital/time period, v = 2πr/T

Question 8

how to classify stars:

Answer 8

(hottest) blue, blue-white, white, white-yellow, orange, red (coldest)

Question 9

life cycle of Solar Mass Stars

Answer 9

stellar nebula -> average star -> (main sequence star) -> red giant -> planetary nebula -> white dwarf

Question 10

life cycle of Larger Stars

Answer 10

stellar nebula -> massive star -> (main sequence star) -> red supergiant -> supernova -> neutron star or black hole

Question 11

gravity:

Answer 11

-isaac newton published his theory of gravity
-depends on: masses of 2 objects + distance between the 2 objects
-distance gets greater = gravity decreases
-mass increase = gravitational force is stronger

Question 12

planets:

Answer 12

8 - planets
-Mecury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune
-planets that are the furthest from the sun feel the weakest pull and follow the least curved path
-planets that are closest to the Sun feel the greatest attraction and so follow the most curved paths

Question 13

nebula:

Answer 13

-all stars form from a giant cloud of hydrogen gas + dust

Question 14

protostar:

Answer 14

-the force of gravity pulls the dust + gas together to form a protostar
-the temp- rises as the star gets denser and more particles collide with each other
-when the temp. gets high enough, hydrogen nuclei undergo nuclear fusion to form helium nuclei
-this gives out a huge amount of energy, which keeps the core of the star hot = star is born

Question 15

main sequence star:

Answer 15

-the star enters a long stable period. during this period, the outward pressure cuased by thermal expansion balances the force of gravity pulling everything inwards
-in this stable preiod it’s called a main seuqence star and it typically lasts several billion years
-the heavier the star, the shorter the time in the main sequence (the sun is in the middle of this stable period)

Question 16

red giant:

Answer 16

-eventually the hydrogen in the core begins to run out and the force due to gravity is larger than the pressure of thermal expansion
-the star is compressed, until it is dense and hot enough that the energy (and so pressure) created makes the outer layers of the star expand
-the star becomes a red giant (if it is a small star) or a red supergiant (if it is a larger star)
-it becomes red because the surface cools

Question 17

white dwarf:

Answer 17

• a small to medium sized star like the Sun becomes unstable and ejects its outer layer of dust and gas. This leaves behind a hot, dense solid core - a white dwarf

Question 18

supernova:

Answer 18

-big stars, however, start to glow brightly again as they undergo more fusion to make heavier elements
-the expand and contract several times, as the balance shifts between gravity and thermal expansion
-eventually, the explode in a supernova

Question 19

neutron star:

Answer 19

-the exploding supernova throws the outer layers of dust and gas into space, leaving a very dense core called a nuetron star
-if the star is massive enough, it will collapse and become a black hole - a super dnese point in space that not even light can escape from