Astrophysics Flashcards
Define Absolute Magnitude
The apparent magnitude a star would have from a distance of 10 parsecs away
Define Apparent Magnitude
The apparent brightness of a star from Earth (or the eye) expressed on the magnitude scale
Define Airy Disc
The bright central fringe of a refraction pattern from light entering a circular aperture
Name the order of the Spectral Class (hottest to coldest)
O, B, A, F, G, K, M
Define an Absorption Spectrum (in context of stars)
A pattern of dark spectral lines in a continuous spectrum produced by the absorption of photons of precise energy which causes changes within an atom
State the Order of the life of a small star (like our Sun)
Interstellar Cloud, Protostar, Main Sequence, Red Giant, Planetary Nebula, White Dwarf.
State the colour, Spectral Class and some elements within the temperature range of 7500-11000K
Colour: Blue or White (or Bluish White)
Spectral Class: A
Elements: Hydrogen and Ionised Metals
Define Quantum Efficiency
The ratio of photons detected to photon incident (no. of photons arriving and absorbed/total arriving)
Define a Standard Candle
An astronomical object of known intrinsic brightness, for example a supernova that is used to determine astronomical distances.
Explain Schwarzschild Radius
The radius of a black hole between the singularity and the event horizon. The event horizon is where the escape velocity equals to (or greater than) the speed of light.
Name the traits of a Neutron Star
- Small
- Dense
- Has a core made of nuclear matter (or neutrons)
What is Collecting Power proportional to?
Collecting Power is proportional to the objective diameter squared
Name 2 disadvantages of a refracting telescope
- Experiences Chromatic Aberration
- Experiences Spherical Aberration
- High cost (compared to reflecting)
- Usually heavier than reflecting (due to lenses being heavier than mirrors)
What is Pogson’s Law expressed as?
m2 - m1 = 2.5 log (base 10) (b2/b1)
What is a parsec?
It is the distance at which the observed parallax angle of the star is equal to 1 arc second.
What does parallax mean?
The effect whereby the position or direction of an object appears to differ when viewed from different positions.
Define Stephan’s Law
A body, when heated, will emit electromagnetic radiation over a range of wavelengths with a total intensity that is proportional to the fourth power of its absolute temperature.
Define Wien’s Displacement Law
The wavelength of the peak emission intensity is inversely proportional to the absolute temperature of the object.
What does the term black body mean?
A body that absorbs all the radiation incident upon it and reflects none.
What energy level do hydrogen atoms from the Balmer series excite to?
n=2
What are the coldest and hottest colours for stars?
Hottest stars = Blue
Coldest stars = Red (Orange)
What is a protostar?
It is a star in its earliest form of life, from a dense cloud of gas, prior to fusion reactions within the core.
What are the characteristics of the following:
Red giants
Supergiants
White dwarves
Red giants –> Cooler and redder stars. Nuclear fusion of helium occurs in the core, similar mass to that of the sun but with an expanded outer shell.
Supergiants –> Mass typically around 10-100 times that of the sun. Core temperatures are hot enough for nuclear fusion to produce carbon and heavier elements. Also more luminous than other stars.
White dwarves –> Old stars that have a high surface temperature but are not very luminous. Do not generate energy by nuclear fusion, however extremely dense.
Which spectral class of stars have the greatest main sequence lifespans?
Spectral class M (Potentially over 200,000,000,000 years)
What does a star need to create a supernova?
It requires a mass 1.4 times greater than that of the sun.
What does it mean by a type II supernova?
This is a single star, a red giant or supergiant that runs out of nuclear fuel and collapses rapidly under its own gravity, ejecting its outer layers with enormous energy.
What do we call the exotic object at the centre of the supernova remnants?
A neutron star
Define escape velocity
The speed necessary for an object to escape the gravitational pull of another object, such as a planet or star.
Define black hole
It is a region of space-time that has such a strong gravitational field that no particles or electromagnetic radiation can escape from it. (greater than the speed of light)
What is a gamma ray burst and why are they potentially dangerous?
These are thought to be narrow beams of intense radiation that came from a collapse of a supernova. They are potentially dangerous as if they were on a collision course with the Earth it could cause mass extinction.
What is the order of life for a massive star?
Interstellar cloud - protostar - main sequence (for about 10 million years - red giant/super giant - supernova - either a black hole or a neutron star.
What is a type I supernova?
This is a star that accretes (draws in) matter from another star in a binary system until it becomes compressed and runaway nuclear reactions are set off, blasting its matter into space.
