what variable did astronomers classify stars in accordance of
temperature
why is temperature a good variable to go by
- stars with similar temps share many other features
- like similar spectral outputs and chemical composition
what are the spectral classes of stars from hottest to coolest
O, B, A, F, G, K, M
what is the mnemonic for remembering the classes in order from hottest to coolest
- Oh
- Be
- A
- Fine
- Girl,
- Kiss
- Me…?
what do the temperatures range from in class O and M
- in class O it is 28,000 - 50,000K
- in class M it is 2000 - 3500K
how do the colours of the stars change down the classes
they change from blue to red
how do the masses of the stars change down the classes
the masses decrease down the classes
how do the radii of the stars change down the classes
the radii decrease down the classes
how does luminosity of the stars change down the classes
the luminosity decreases down the classes
how do the lifespans of the stars main sequence lifespan change down the classes
the lifespans increase down the classes
why do hotter stars tend to have more mass and luminosity
- the larger gravitational pressure from the larger mass makes nuclear fusion within the star faster
- this produces a lot more energy at a quicker rate
- with that being the definition of power, luminosity increases
- as well as more thermal energy being released
what other factor results in hotter stars having a higher luminosity
- hotter stars are usually bigger
- the increased surface area allows for more luminosity
- as there is more room for power to be outputted
why do hotter stars have shorter main sequence life spans
- because nuclear fusion occurs at a quicker rate within their cores
- this means they run out of hydrogen fuel quicker than cooler stars
- leading to heavier elements being fused sooner, therefore having a shorter M.S. lifespan
why do the colours of the stars change across the classes like so
- hotter stars would emit shorter peak wavelengths as they have more energy
- this would correspond to the the blue end of the visible spectrum
- with cooler stars the wavelengths are longer, showing up as red
why does hotter stars emitting shorter wavelengths mathematically make sense
- the equations say so
- Ymax T = 2.898x10-3, a constant
- so for temp to increase, Ymax must decrease
- even in E = hf, a higher energy wave needs a higher frequency
- with v being constant in v=fY, an increase in f leads to a decrease in Y
what is the relationship between peak wavelength and the colour of the star
the peak wavelength, in the range of the visible spectrum, determines the colour of the star
what are the axes for the hertzsprung-russell diagram
- temperature (K( is the x axis
- it starts off with the highest temperature then decreases along the axis
- luminosity (compared to the sun) is the y axis
- ranging from 10^-6 to 10^6 with 1 in the middle, being the luminosity of our sun
what does the diagram generally look like
- several different clusters of dots, being stars
- with each cluster representing a type of star
where is the cluster of main sequence stars
- they stretch diagonally across the diagram with a negative gradient
- ranging from 20,000K at 10^4 to just over 2500K at 10-4
what type of stars form a small cluster at the bottom left of the diagram, in between 10,000 and 20,000K with limited luminosity deviation between them
white dwarfs
where is the cluster of supergiants
- they form a short horizontal line at the very top right
- ranging from 2500 to 7000K but staying in between 10^4 and 10^6
what type of stars form a small cluster below supergiants but above main sequence stars, with the dots curving like an x^1/2 graph
giants
