2.1 - star magnitudes

how did hipparchus classify stars?

by their brightness to the naked eye (i.e., intensity of light received);

• 1 = brightest

• 6 = dimmest

what is brightness?

intensity of light received

which feature of stars did hipparchus classify his stars by?

their brightness to the naked eye

in hipparchus’ star classification, which objective point was the brightness measured from?

the naked eye

how did hipparchus’ scale range?

1 = brightest

6 = dimmest

for hipparchus star classification, what does a star of brightness 1 mean?

it was the brightest

for hipparchus star classification, what does a star of brightness 6 mean?

it was the dimmest

what were the problems with hipparchus’ classification?

• he did not measure the brightness of the sun, so questions were raised where to class the sun

• only considered stars emitting visible light

• subjective, therefore not accurate

• the invention of telescopes led to it’s discontinuation

why was the invention of telescopes a problem for hipparchus’ classification?

was hipparchus’ scale objective or subjective?

subjective

why was hipparchus’ scale subjective?

• it relied on the observer’s own opinion on how bright a star is, which could vary between observer’s

• it didn’t account for any problems the observer had with their vision that could affect how they perceived the brightness of a star

why does the subjectivity of hipparchus’ scale affect the classification’s accuracy?

the brightness of stars could not be considered as the objective truth because it’s classification is purely subjective, which means the value of brightness could vary between different observers

what didn’t hipparchus consider in his scale?

the brightness of our sun

why was it a problem that hipparchus didn’t measure the brightness of our sun?

because now we don’t know where to class the sun on his scale

what were the only kinds of stars hipparchus considered in his scale?

stars that emit visible light

why did hipparchus only consider stars that emit visible light in his scale?

his scale considered brightness. if a star did not emit visible light, it’s light intensity could not be measured, therefore stars that didn’t emit visible light would not be considered

why was it a problem that hipparchus only considered stars that emit visible light in his scale?

it did not consider a wholistic view of the stars in the universe, as not all stars emit visible light