Space Physics Flashcards
Orbital speed
2Πr/T
r - average radius of orbit
T - orbital period
Hubble constant
Ho = 2.2 x 10^-18
Formula hubble constant
v/d
Age of the universe
d/v = 1/Hubble constant
1 light year
9.5 x 10^15
Milky Way diameter
100 000 light years
How much time does Earth take to rotate on its axis?
once every 24h
Time taken for Earth to orbit Sun
365 days
Why do we experience seasons?
Slight tilt of earth’s axis
eg: December: northern hemisphere angled away from Sun (less sunlight, winter)
southern hemisphere towards Sun (more sunlight, summer)
How long does it take the Moon to orbit the Earth?
1 month
Order of planets from sun
Mercury
Venus
Earth
Mars
Jupiter
Saturn
Uranus
Neptune
How many stars in our solar system?
One, the Sun
What are some examples of minor planets that orbit the Sun?
minor planets, like dwarf planets (Pluto)
asteroids in the asteroid belt
What is a moon?
A natural satellite of a planet
What are some other smaller Solar System bodies?
comets and natural satellites
What are natural satellites?
an object that orbits a planet or another body that is larger than itself
What are comets?
balls of ice
orbit the Sun elliptically, and when they come close to the Sun, they heat up, and some of the ice evaporates, becoming a visible tail
How can you describe the four innermost planets in the Solar System?
rocky and small
How can you describe the four outermost planets in the Solar System?
large and gaseous
Explore the accretion model
Slowly, dust from interstellar clouds gradually clumped together because of its own gravity, began to spin as a disc, eventually most ignited, became the Sun.
Particles in remaining disc of dust began to clump together and grow into larger and larger chunks, pulled together by gravity.
Close to the Sun, high temp: materials like H and He (low BP) could not solidify into planets. Heavier elements like iron were the only ones that could form planets close to the Sun. Planets closest to Sun became rocky planets, hydrogen and helium pushed further out.
Further from the Sun: H and He condense into a liquid to form planets
Why is the accretion model called this?
Because the planets slowly gain (accrete) mass over time as their gravity attracts more material.
Effect of gravity on accretion model
The bigger the mass, the greater the gravitational field strength at its surface.
All the planets orbit Sun since it contains almost all the mass of the Solar System therefore a much stronger gravitational pull than anything else
Describe orbit shapes
Planets, minor planets and comets have elliptical orbits, Sun is not at centre (except when orbit is approx. circular)
Explain planet’s movements in an elliptical orbit.
Planets move faster when it is closest to the star.
Conservation of energy:
As planet gets closer to the star, GPE is converted into KE – so it moves faster.
As it travels away, its KE is converted back into GPE, so it slows down.
Correlation between orbital distance and orbital speed
When orbital radius is greater, the planet moves more slowly.
What does the strength of the gravitational field at the surface of a planet depend on?
mass of planet
Correlation between strength of gravitational field around planet and distance from planet
Strength around a planet decreases the further you get away
Why do the planets orbit the Sun?
because it contains most of the mass of the Solar System
What keeps an object in orbit around the Sun?
force: gravitational attraction of the Sun
What happens as you get further away from the Sun?
Sun’s gravitational field decreases
Orbital speeds of planets decrease
Describe the Sun.
- star of medium size
- consists mainly of hydrogen and helium
- radiates most of its energy in infrared, visible and ultraviolet regions of em. spectrum
What are stars powered by?
nuclear reactions that release energy
How are the nuclear reactions in stable stars?
fusion of hydrogen into helium
What are galaxies made up of?
many billions of stars
Many billions of stars make up…
galaxies
Where is the Sun located in?
in a galaxy known as the Milky Way
What is the relative distance of stars in the Milky Way?
other stars are much further from Earth than the Sun from Earth
How can astronomical distances be measured?
light-years
What is a light year?
distance travelled in the vacuum of space by light in one year
How is a star formed?
from interstellar clouds of gas and dust that contain hydrogen
What is a protostar?
an interstellar cloud collapsing and increasing in temperature as a result of its internal gravitational attraction. emits light.
When does a protostar become a stable star?
when inward force of grav. attraction is balanced by an outward force due to high temperature in star’s centre
What will eventually happen for all stars?
they will all eventually run our of hydrogen as fuel for the nuclear reaction
What happens to stars when most of the hydrogen in its centre has been converted to helium?
most expand to form red giants. more massive stars expand to form red supergiants
What does a red giant from a less massive star form?
a planetary nebula with a white dwarf at its centre
What does a red supergiant form?
- explodes as a supernova
- forming a nebula containing hydrogen and new heavier elements,
- leaving behind a neutron star or black hole at its centre
After a supernova, what may happen?
the nebula from a supernova may form new stars with orbiting planets
What is redshift?
an increase in the observed wavelength of e.m radiation emitted from receding stars and galaxies
Why do we see redshift?
light emitted from distant galaxies appears redshifted compared to light emitted on the Earth
What is redshift in light from distance galaxies evidence for?
Universe is expanding, supports Big Bang Theory
What is cosmic microwave background radiation (CBMR)?
microwave radiation of a specific frequency is observed at all points in space around us
When was CBMR produced? What happened to this radiation?
- shortly after Universe was formed
- this radiation has been expanded into the microwave region of the em spectrum as the Universe expanded
How can we find the speed v at which a galaxy is moving away from the Earth?
the change in wavelength of the galaxy’s starlight due to redshift
How can we determine the distance of a far galaxy d?
using the brightness of a supernova in that galaxy
Define the Hubble Constant H0.
ratio of the speed at which the galaxy is moving away from Earth to its distance from Earth
v/d
d/v=
1/H0
1/H0=
d/v
What is the equation 1/H0 = d/v?
- estimate for age of Universe
- evidence for idea that all matter in Universe was present at a single point
H0 =
v/d
estimate for H0
2.2 x 10^-18
