Physical Properties of Stars Flashcards
Why are stars in a constellation are not physically related but that stars in a cluster are associated with one another.
Although stars in a constellation appear to be physically related to one another, this is merely a line of sight effect. However the same does not apply to stars in a cluster which are linked gravitationally.
What is the difference between binary stars and optical double stars.
Optical double stars appear to be closely-aligned (one star may be many times further away from the other), whereas stars in a binary system are the same distance from us and orbit their common centre of gravity.
What is the apparent magnitude scale.
Difference in Magnitude Brightness Ratio
1 2.5
2 6.25
3 16
4 40
5 100
Describe the method of heliocentric parallax to determine distances to nearby stars.
This is called heliocentric parallax. You can measure the distance to nearby stars by measuring how much they appear to move against distant stars. You measure it in one month and then again six months later when the Earth is on the opposite side of the Sun.
Recall the definition of one parsec (pc).
A parsec (3.26 light years).
Recall the definition of absolute magnitude.
It is the brightness of a star at a distance of 10 parsecs which is 32.6 light years.
Demonstrate an understanding of the inverse square law nature of the intensity of light.
The effect of sunlight works like this. If say we are three times as close to the Sun as Earth it would get not 3 times as much light but 9 times as much (the square of 3 is 9).
What is a cepheid variable?
A Cepheid variable is a star that pulses frequently. We see the light they produce dip and rise over a short period of time, returning to the same luminosity a few days later.
Demonstrate an understanding of what information can be obtained from a spectrum, including chemical composition, temperature and radial velocity.
We can tell what atoms are present by different coloured lines in the spectrum. Some lines are dark and called absorption lines. These show what atoms are absorbing the light. Some lines are bright and show what atoms are emitting light. These are emissions lines.
So if there are darker lines that show Hydrogen and bright lines that show Helium we can say that the star has finished burning its Hydrogen and started burning Helium.
Demonstrate an understanding of how stars can be classified according to their spectral type.
Type Colour Temperature Spectral lines
O Violet -white 30,000° K+ Helium with Hydrogen
B Blue-white 12,000 - 30,000° K Hydrogen with Helium
A White 8,000 - 12,000° K Hydrogen Rich
F Yellow-White 6,000 - 8,000° K Calcium
G Yellow 5,000 - 6,000° K Some Iron lines
K Orange 3,000 - 5,000 ° K Many Metallic lines
M Red <3,000 ° K Metallic and Carbon lines
