cas Beta – 55ly Alpha- 230ly Gamma- 615ly Delta- 100ly Epsilon- 440ly

Magnitude Absolute vs. Apparent

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The analogy Imagine a birthday candle and a spotlight are both 50 feet in front of you Which would be brighter? Now move the candle right in front of your face. Put the candle back and move the spotlight 1000 feet away.

Magnitude = Brightness Brightness is measured in two ways: Absolute Visual Magnitude (M) - the actual luminosity of the star based on energy output. Candle and flashlight at same distance Apparent Visual Magnitude (m) – how bright the star appears (depends on distance) Candle/flashlight at different distances

abs

Apparent Magnitude cas Beta – 55ly Alpha- 230ly Gamma- 615ly Delta- 100ly Epsilon- 440ly

Aparrent

Using Abs. and App. Magnitudes Absolute mag. (M) = apparent mag (m) at a distance of 10 parsecs (Baseline Distance) Star is closer than 10 parsecs then Apparent is brighter (If m is higher than M, star is closer than 10 parsecs) Star is farther than 10 parsecs, Absolute is brighter (If m is lower than M, star is further than 10 parsecs

Distance Modulus A value that helps us get an estimate of distance. DM = M-m (Distance Modulus = Absolute Mag – apparent mag) If positive, apparent is smaller (brighter), star is closer than 10 parsecs away More positive means more closer (way more positive means way more closer) If negative, apparent is larger (dimmer), and the star is farther than 10 parsecs away More negative means more fartherer

History of Magnitudes Hipparchus (maybe Ptolemy?) – 2000 BCE A ranking system Brightest stars = 1st class, then 2nd, 3rd… 6th magnitude are faintest stars seen at night Result: lower number = brighter “There is no other rule for classing the stars but the estimation of the observer; and hence it is that some astronomers reckon those stars of the first magnitude which others esteem to be of the second.” (Ewing 1812)

Why Negative? 1856 proposal to standardize standard ratio of 2.512 between magnitudes. 5 magnitude steps correspond to 100x factor brightness change The Star Vega selected as baseline (magnitude 0.0) 5th brightest star, 2nd in North hemisphere Is now magnitude 0.03, by redefined baseline scale Made it possible to go brighter than first class 0th class? -1st class? And so on.

Essential skills Know the difference between Absolute and apparent magnitudes Know how to compare Absolute and Apparent magnitudes to estimate stellar distances (the “distance modulus” or M-m) Know when Abs. and App. are the same (what distance for M=m)

Animation Hypothesize. What could make an object look brighter or dimmer compared to others?