Light year

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To measure the distance of a planet
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Astronomers use a baseline of
1 astronomical unit (AU),
which is the average distance
between Earth and the sun.
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BSL Version

BSL – Explaining of distance

• Sun >> Mercury
  (distance of 0.47AU = 36 million miles)
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• Sun >>>> Earth
  (distance of 1AU = 93 million miles)
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• Sun >>>>>>>>>>>> Jupiter
  (distance of 5.27AU = 483,600,000 million miles)

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• nearby stars distance is calculated by measuring the slight shift in angle of each star in comparison to stars far away, as the Earth orbits the Sun; this is called “Parallax Shift”.
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• parallax shift, it can only be used to measure nearby stars, so astronomers work out the distance to faraway stars and galaxies by comparing how bright they look with how bright they actually are.

BSL Version

• explaining about parallax shift

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• beyond classification and evolution, the Hertzsprung-Russell diagram offers invaluable insights into the fundamental properties and characteristics of stars.
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• each star’s position on the diagram reveals crucial information about its;
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  – luminosity
  – surface temperature
  – radius
  – mass
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• these classes have particular colours. Spectral type is most often written across the top of the H-R diagram going from hot, blue “O” stars (very hottest, brightest stars) on the left to cool, more red “M” stars (very coolest, dimmest stars) on the right.
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• the seven spectral classes in order of surface temperature from hottest to coolest are;
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O B A F G K M

BSL Version

• explaining about the hottest and coolest stars.