Ast 105 1st Edition Lecture 8 Outline of Previous LectureI. Spectral Classesa. Remember by: Officially, Bill Always Felt Guilty Kissing Monica II. Stellar Massa. Binary Star Systemb. Kepler’s 2nd and 3rd Laws Outline of Current LectureI. Apparent Magnitude a. Brightness of starsII. Absolute Magnitude a. Accounts for distance as well as brightness/luminosity Apparent Magnitude- Early astronomers classified stars by how bright they appeared in the night sky. During this time, it was assumed that all stars for the same distance from the earth.- We call the brightness of stars, ignoring their distance from Earth, apparent magnitude use little “m” brightness=magnitude- brighter the star, the smaller the m - brightest stars are me=1- Stars that were about half as bright m=2- dimmest (still visible to unaided eye) m=6- it was determined that an m=1 star was 100x brighter than an m=6 100 m=6 stars provide as much light as a single me=1 star - Keck and Hubble telescopes can detect stars as dim as an m=30- Each successfully brighter star is about 2.5x brighter than the preceeding magnitude - Bright objects Venus: m=-4.4 Moon: m=-12.6 Sun: m=-26.7- Dim object Pluto is about m=15.1Absolute Magnitude These notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.- Stars that are farther away will appear dimmer simply because the intensity of light varies as 1 divided by distance2 Light is an inverse square law - Our sun has a luminosity of 3.8x1026 watts This light spreads out - To determine the total power of a star, we need to account for distance - To handle distance, they move each star to 10 parsecs from earth. So this light is now called absolute brightness/magnitude- Range: m=-10 (brightest) m=17 (dimmest) M=Absolute magnitude m= Apparent magnituded=distance Relation: M = m –
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