Physics__Space Flashcards
What is luminosity?
L - Total output power of a star, unit W
Whats radiation flux/Intensity?
I/F - The electromagnetic wave energy per second per unit area from a star reaching us on Earth Or the power received from a star per unit area
What are radiation flux/Intensity and luminosity linked by?
Inverse-square law
Whats an arcsec?
1/3600*
What’s one minute of an arc?
1/60*
What’s a light year?
The distance travelled by light in one year 9.5 x 10^15 m
What’s a standard candle?
A distant star of known luminosity
How do you find the distance d from Earth to a distant star?
Locate a Cepheid variable star.
Measure its T.
Find the star’s luminosity, L, using Leavitt’s T-L data.
Measure the radiation flux, F, from the star at Earth.
Calculate d using d = root(L/4 * PI * F)
What are the stages in the early life cycle of a star?
Nebula - A giant cloud of H gas and dust. Gravitational attraction between atoms forms denser clumps of matter. Inward movement of matter is called gravitational collapse.
Protostar - Graviational collapse causes the gas to heat up and glow.
Nuclear Fusion - Eventually temperature reaches millions of degrees K, and fusion of H nuclei to He nuclei begins.
Main Sequence - The star reaches a stable state when inward and outward forces are in equilibrium. As T increases and V decreases, gas pressure increases.
How can we detect protostars?
With telescopes which can observe infrared radiation.
What stages follow the main sequence for low mass stars? (<1.4 x mass of sun)
Red Giant - Nuclear fusion slows, so star shrinks and them swells and cools forming a red giant. Fusion continues in the shell around the core.
Planetary Nebula - Outer layers of star are released
White Dwarf - Solid core collapses under its own mass, leaving behind a very hot dense core.
What stages follow the main sequence in massive stars? (>1.4 x mass of sun)
Red Super Giant - H fuel runs out and nuclear fusion slows. Star shrinks then swells and cools.
Fusion continues in the shell around the core. The shell burning and core burning cycle in massive stars goes beyond that of low-mass stars, fusing elements up to iron.
Supernova - iron core collapses, outer shell is blown out in an explosive supernova.
Neutron Star/Black hole - Collapsed neutron core can remain intact having formed a neutron star.
What’s Wein’s law?
The black body radiation curve for different temperatures peaks at a wavelength that is inversely proportional to the temperature.
Lambda max*T = 2.898 x 10^-3 m K
What does Wein’s law tell us when: the higher the temperature of a body…
The higher the temperature of the body… the shorter the wavelength at the peak intensity, so hotter objects tend to be white or blue and cooler objects tend to be red or yellow.
The greater the intensity of the radiation at each wavelength
What’s the Stefan-Boltzmann Law?
The total energy emitted by a black body per unit area per second is proportional to the fourth power of the absolute temperature of the body.
What’s the Stefan-Boltzmann Law equation?
L = sigma A T^4
L = luminosity of the star (W),
A = surface area of the star,
sigma = the Stefan-Boltzmann constant,
T = surface temperature of the star (K) ,
The surface area of a star (or other spherical object) can be calculated using: A = 4 PI r^2
Describe the characteristics of main sequence stars
Stars are converting hydrogen to helium in their core. Stars on main sequence maintain a constant luminosity (for most of their lifetime)
How do you find the distance from Earth to a nearby star?
Stellar Parallax
- The star is viewed from two positions at 6 month intervals.
- The change in angle of the star against a backdrop of fixed stars is measured.
- Use trigonometry to calculate the distance to the star. The diameter of the the Earth’s orbit about the sun must be known
Hertzsprung Russel Diagram
What is a suitable method to measure the distance to:
A nearby star
Nearby galaxy
Very distant galaxy
Nearby star: parallax
Nearby galaxy: standard candle
Very distant galaxy: red shift
How is Doppler shift used
- Measure frequency/wavelength emitted by the star
- Determine difference between this frequency/wavelength and that emitted in the lab
- Determine speed of star relative to Earth v/c = change in f/f0
- Velocity is approaching when the frequency has increased and receding when the frequency has decreased
What’s Hubble’s law?
- The speed of recession of a galaxy v is proportional to its distance from Earth d. The constant of proportionality is the Hubble constant.
- 1/Hubble constant (H0) = age of the universe
