# 2 - -Cannon re-organized the spectra types to form a...

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Apparent magnitude (m) and Absolute magnitude (M) are related to distance: M = m-5 log (d/10) The Apparent magnitude (m) is easy to measure For certain stars (like Type la supernovae) we can also determine the Absolute magnitude (M) Then we can compute distance!! (in parsecs): D = 10 (5 + m-M)/5 Different Types of Star (How many are there?) - To understand the diversity of stars, we first classify them. - We can use the star’s spectrum to do this. - This was first done in the early 1900’s at Harvard university by Annie Jump Cannon - She was assigned the job of classifying stellar spectra into types (A,B,C…) - In her life she classified over 200,000 spectra!! - Cannon found that most stars fell into 7 different categories - A stars spectral lines depend on what its temperature is
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Unformatted text preview: -Cannon re-organized the spectra types to form a temperature sequence: O,B,A,F,G,K,M (hot to coolest) – “oh be a fine girl kiss me” How Do We Classify Stars?-O type stars are the hottest-M type stars are the coolest Spectral Sub-Type OBAFGKM-A star’s spectral type can be specified more precisely using a subtype ranging from 0 to 9.-Example: spectral type A is divided into A0,A1,A2…A9-A0 is the hottest, and A9 is the coldest.-F0 is cooler than A9-If you know a star’s spectral type, then you know its temperature.-The sun is a type G2 star, corresponding to a temperature of 5800 K Stars: What do we know?-Temperature (T) & Spectral Type-Distance-Brightness 1. Luminosity (Lstar) – energy output of a star...
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## This document was uploaded on 10/07/2011.

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