D - Astrophysics Flashcards
What are characteristics of asteroids?
- orbiting the sun, similar like planets but much smaller
- those less than 300km have irregular shape (gravity too weak to compress them into shperes)
Bigger ones 1000 km wide considered as minor planets
most in the asteroid belt situated between mars and jupiter
What are comets ?
irregular objects - a few kilometers only
comprising of gases rock and dust
sharp elliptacal orbits around the sun with periods up to thousand years
near sun the gases in a comet are vaporized forming a comet tail
What is a main sequence star?
What is hydrostatic equilibrium ?
A star in the phase when hydrogen is fused into helium.
A star in this phase in a hydrostatic equilibrium that is stable for billions of years:
Radition pressure (from fusing hydrogen to helium) opposes the inward gravitational forces
What are binary stars?
Binary stars consist of two stars that rotate about a common centre of mass.
What are nebulae ?
intergalactic cloud of dust
usually ejected from a supernovae
stars are born from nebulae
How many stars has the milky way approximately?
What kind of galaxy is the milky way?
3 x 1011
Spiral galaxy
It is assumed that all such galaxies have a black hole in its center.
What is a stellar cluster ?
A group of stars that are close enough to be held together by their gravity
number ranges from dozens to millions
What is a lightyear ?
Distance, light travels in one year.
1ly = 9.46 x 1015 m
What is an astronomical unit AU ?
The average distance between sun and earth.
approx 8 lightminutes
What is an arcsecond?
1 arc = 1 degree (put of a 30g deg circle)
1 arc minute is 1/60 of an arc
1 arc second is 1/60 of a minute or 1/3600 of an arc
Explain the term stellar parallax.
A star is looked at in July and January.
In this time earth moved 180 deg to the other side of the sun.
the star appears to have moved across the fixed stars in the background.
The parallax angle (measured in arc seconds) is the angle the star has apparently moved.
Technically angles can be measured up to 0.01 arcseconds. More distant stars cannot be measured with this method.
What is the luminosity of a star (definition and base unit?)
- Total power of emitted (all radiates in all wavelength)
- Measured in Watt (Unit for Power)
What are the two properties of a star are needed to determine the luminosity? (Stefan-Boltzmann Law)
Temperatur and size of surface L = σA T 4
What is apparent brightness of a star ?
What variables need to be known to calculate the apparent brightness ?
The apparent brightness is the incident power per unit area received at the surface of the Earth.
To calculate it you need to know
- the power the star emits (which is its luminosity)
- the distance from the star
How do arc seconds and parsecs relate ?
parsecs is the distance of a star from earth which parallax angle is 1 arcsecond
parallax angle is the angle the star apparantly “moves” when looked at from the earth in July and December (when the earth actually moved to the other side of the sun.)
