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

2. Magnitude
Absolute vs. Apparent

3. 2

4. 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.

5. 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

6. abs

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

8. Aparrent

9. 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

10. 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

11. 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)

12. Why Negative? 1856 proposal to standardize
standard ratio of 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.

13. 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)

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