Astrophysics (Stellar Quantities) Flashcards
What are Galaxies?
How about groups of them?
Galaxy - A collection fo a very large number of stars mutually attracting each other through the gravitational force
Groups of galaxies = Clusters of galaxies
Groups of Clusters = Super Clusters
What are Comets
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What are Stars
A luminous sphere of plasma held together by its own gravity
What are Binary Stars
Two stars orbiting a common center of mass
What are Stellar Clusters?
Open and Globular?
A group of stars gravitationally bound together.
Physically close together and formed around the same time
Open Stellar Clusters:
Globular Stellar Clusters:
What are Nebulae
interstellar clouds of dust, hydrogen, helium and other ionized gases.
They are the remains of a previous star that has reached the end of its lifecycle and died.
What is the nature of a star? (how are they in daily life?)
The stability of a star depends on the HYDROSTATIC EQUILIBRIUM between two opposing forces:
- gravitation which can collapse the star
- radiation pressure which can make the star expand.
This equilibrium is gained through nuclear fusion which provides the energy the star needs to keep it hot so that the star’s radiation pressure is high enough to oppose gravitational contraction
What is a Stellar Parallax
Stellar Parallax – apparent shift in position
When observing a nearby star against a background of distant stars on two different occasions six months apart, the target star image will appear to have shifted against the more distant stellar background.
one half of the measured shift in apparent position is deemed the “stellar parallax” of the target.
If a star has a parallax angle of exactly one arc-second (see below), it would be 3.8x1016m away (1 parsec);
Parsec = distance of star with 1 arc-second
if a star is too far away from Earth, its parallax will be too small to be measured with accuracy. This is at around 100 parsecs.
What is the nature of a star? (how are they in daily life?)
The stability of a star depends on the HYDROSTATIC EQUILIBRIUM between two opposing forces:
- gravitation which can collapse the star
- radiation pressure which can make the star expand.
This equilibrium is gained through nuclear fusion which provides the energy the star needs to keep it hot so that the star’s radiation pressure is high enough to oppose gravitational contraction
Define Apparent brightness
Apparant Brightness (b) - power received per unit area of a surface of an observer planet from a distance to the source *Measured in Watts per square meter (W*m^-2)
The apparent brightness of a star will decrease with distance, because the light is spreading over a bigger area, being less powerful
Define Intensity
Intensity (I) - Power per unit area
Measured in Watts per square meter (Wm^-2)
What is the Astronomical Unit
(AU) - distance of sun to the earth
