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Chapter 12.Measuring the Properties of Stars

Chapter 12.Measuring the Properties of Stars - Measuring...

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1 Measuring the Properties of Stars Chapter 12

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2 Which star looks like it is giving off more light? But which star is actually giving off more light?
3 Do all stars appear the same? Which one looks the coolest? How can we describe the brightness of stars?

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4 The basic problem in astronomy is the determination of distance . If we cannot measure the distance to an object, we won’t know its intrinsic brightness, only its apparent brightness. If we don’t know its intrinsic brightness, we can’t determine how much energy it emits and, hence, can’t construct a theoretical model that explains it.
5 Our Goal: We would like to compare the properties of other stars (Luminosity, Temperature, what the star is made of), to the Sun, so we can better understand the stars in general. However, it turns out that it is very difficult to measure Luminosity in an easy way. We have to start with what we actually see, and then convert that measurement to Luminosity.

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6 As the Sun sets, some stars are visible. These are the first magnitude stars. Later, when twilight is over, more stars are visible. These are the second magnitude stars, and so on …But are the brighter stars closer?
7 Apparent Magnitude is a number that represents the apparent brightness of stars as seen on Earth The larger the number the dimmer the star will appear from Earth N ote: we use the letter “m” for apparent magnitude

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8 Smaller/negative numbers mean BRIGHTER stars and Bigger/positive numbers mean DIMMER stars This is opposite of Luminosity (energy/time), where the larger the number, the brighter the star.
9 How do we find the distances to stars? The PARSEC (pc) is defined as the distance in which a star has a parallax of 0.00027 degrees as observed from the Earth. A quarter, viewed from 3.1 miles away, has this same angle!

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Chapter 12.Measuring the Properties of Stars - Measuring...

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