TEMPERATURE

A star’s color depends on its surface temperature

How hot is Vega?

l (Å)

lmax at 4600 Å

BB spectrum

So, Wien’s law tells us

K630010x4600

10x8977.210

3

VegaT

Vega is 500 Khotter than the Sun

SPECTRUM

Never Say Never• Auguste Comte (1798 - 1857)– French Philosopher (bad prophet)– Founder of the Social Sciences– Espoused the philosophy of positivism – as seen on the

Brazilian flag – “Love as a principle and order as the basis; progress as the goal.”

“there is no conceivable means by which we shall one day determine the chemical composition of the stars”

Continuous spectrum

l

l

Blackbody spectrum

Classify Stars into groups based on Spectral Data

The Spectral Sequence• In 1890, Edward Pickering and

his assistant at Harvard classified thousands of stellar spectra at Harvard.

• Named them ‘A’ through ‘Q’

• A. Cannon ‘improved’ the scheme and ordered it by temperature: O,B,A,F,G,K,M

• Subdivided each into 0 through 9 (AO: hot – A9:cooler)

E. Pickering and his housekeeper W. Fleming

A. J. Cannon classifying one of 200,000 spectra by eye for 25¢ an hour ($6 today)

Annie Jump Cannon (1863 - 1941)studied over 250,000spectra as part of theHarvard Observatory

program to classify stars

Spectral Type Classification System

O B A F G K MOh Be A Fine Girl/Guy, Kiss Me (Long Time)!

50,000 K 1,000 K Temperature

Only Brilliant Astronomers Find Glorious Knowledge Manning Large Telescopes

Only Boring Astronomers Find Gratification Knowing Mnemonics Like That…

MAGNITUDE

Star Apparent Magnitude

Distance (pc)

Absolute Magnitude

Luminosity (Sun=1)

Sun -26.74 - 4.83 1

Sirius -1.44 2.6371 1.45 22.5Arcturus -0.05 11.25 -0.31 114Vega 0.03 7.7561 0.58 50.1Spica 0.98 80.39 -3.55 2250Barnard's Star 9.54 1.8215 13.24 1/2310

Proxima Centauri 11.01 1.2948 15.45 1/17700

Flowchart of Key Stellar Parameters