Astrophysics Flashcards
Solar System Order
Sun Mercury Venus Earth Mars Jupiter Saturn Uranus Neptune
Mercury
Rocky
closest to sun
smallest planet
no moons
no atmosphere
Venus
Rocky
hottest planet (nearly 500 degrees c)
thick atmosphere
Mars
rocky
the red planet due to large amounts of iron oxide in the surface
Jupiter
gas
the biggest planet
Saturn
gas
has rings
Asteroids
lumps of rock
most are found between mars and jupiter in the asteroid belt
Comets
made of ice and dust
takes hundreds of years to orbit the sun in a highly elliptical orbit
as they get close to the sun they melt (hence leaving a tail)
Planetary system
a group of planets orbiting a star
Binary stars classification
visual - can be seen as two different stars
eclipsing - detected by periodic variations in brightness as one star obstructs the other
spectroscopic - detected by changes in the wavelength of light received from each star (due to Doppler effect)
Galaxies
a galaxy is a large scale collection of stars, gas and dust held together by gravity
Stellar cluster
a close group of gravitationally bound stars, gas and dust
Galactic cluster
a group of galaxies gravitationally bound together
larger groupings of galactic clusters are called superclusters
Nebula
is an intergalactic cloud of dust and gas
Constellations
certain stars appear to make patterns in the sky
these stars are not necessarily close together
one AU
mean distance from the centre of the earth to the centre of the sun
light year
distance light travels in a year
Method of Stellar parallax
- the stars apparent position relative to background stars is noted at 6 month intervals
- using trigonometry tanp= earth-sun distance/sun-star distance
- as p is a very small angle tan p = sin p = p in radians
- this means that the smaller the angle p, the greater the distance to the star
- the angle p is so small that it is measured in arc-seconds (1/3600th of a degree)
- the distance to the star (d) and the parallax angle (p) are related by the following formula d(parsec) = 1/p(arc seconds)
parallax angle
half of the observed angular displacement of the star
parsec
the distance at which the angle subtended by the radius of the earth’s orbit is one arc-second
Limitations of Stellar parallax
at greater distances, the parallax angle becomes too small to be accurately measured (i.e. the uncertainty becomes larger than the value)
Why are stars stable?
there is an equilibrium between the outwards radiation pressure and inwards gravitational pull
Luminosity
the total amount of energy emitted per second by a star
Apparent brightness
is the amount of energy from the star recieved per unit area by an observer
Stellar spectra
atoms in cooler atmospheres are exited absorbing photons of certain energies these transitions appear as dark absorption lines
this can tell us:
- what elements the star is made of
- the temperature of the star
- how the star is moving
Red giants
red in colour (cool)
large mass
large surface area
are in a late stage of the stars life cycle
Red supergiants
red in colour (cool)
very large mass
very large surface area
are in a late stage of the stars life cycle
White dwarfs
white in colour
small mass
small surface area
final stage in the life cycle of smaller stars
no longer undergoing fusion (cooling)