H.A.L. Astronomy School

H.A.L. Astronomy School

Star Stuff:Or, Interesting Stuff to Know

and Tell about Stars

1930 hours EDT

2030 hours EDT

2130 hours EDT

Kochab

Proper Names  Kochab  KocabBayer Designation  Beta Ursae MinorisFlamsteed Number  7 Ursae MinorisBSC  5563HD  131873Constellation  Ursa MinorRight Ascension  14h 50m 42sDeclination  +74° 9' 20“Distance  127 light years  39 parsecsMagnitude  Apparent: +2.2  Absolute: -0.8 to -0.7Spectral Class  K4  Orange GiantOptimum Visibility  April/May  Usually visible from  northern latitudes

How’s the “seeing”? Using Certain Stars to Determine Limiting Magnitude

The 2,3,4, and 5 System:

An Illusion of Permanence: At a Casual Glance

Heavens seem eternal and unchanging

Sky we see at night is virtually indistinguishable from the sky seen by our ancestors

Empirical Reality, 1 of 3 Stars are born even NOW from

interstellar gas and dust, in cold clouds that are scattered abundantly throughout our galaxy

Perhaps an interstellar cloud encounters one of the galaxy’s spiral arms…

Empirical Reality, 2 of 3 …or perhaps a supernova detonates

nearby From the shock of events like these,

the cloud begins to contract under the pull of gravity, forming protostars – the fragments that will one day become stars

Empirical Reality, 3 of 3 As protostar develops, its internal

pressure builds and its temperature rises

In time, hydrogen burning can ignite, and a star is born

Clusters of these young stars illuminate the interstellar gas and dust that surround them, producing beautiful glowing nebulae

Starbirth, starlife, stardeath Stars are born, they mature and they

grow old Major stages in their lives can last for

millions or even billions of years Some even blow themselves apart in

death throes that enrich interstellar space with the material for future generations of stars

Stars Seem Unchanging to Our Eyes

But only because of the colossal time scale over which

they change

150 ly (45 parsecs)

Distance: 23,000 ly (7,000 parsecs)

The average density of stars in M13 is about 100 times greater than in the neighborhood of the Sun.

Stellar census of a few hundred thousand stars

Stellar Astrophysics:The Very Short Course

Mass Matters, 1 of 4 The most massive stars are the most

luminous, while the least massive stars are the least luminous

Observation and theory show that there is a lower and an upper mass limit for stars

Mass Matters, 2 of 4 A protostar less massive than 0.08

solar masses can never develop the necessary pressure and temperature to start hydrogen “burning” at its core

Theory indicates this failed star contracts to become a hydrogen-rich object called a brown dwarf

Brown Dwarfs Brown dwarfs are intermediate in

their properties between stars and Jovian planets (such as Jupiter with a mass of 0.001 solar masses)

Jupiter is NOT a failed star Observational confirmation of brown

dwarfs did not come until 1994 (Gliese 229)

Mass Matters, 3 of 4 Protostars with masses greater than

about 100 solar masses also do not become main-sequence stars

They rapidly become very luminous with pressure so great that it overwhelms the effects of gravity, expelling the outer layers into space and disrupting the star

Mass Matters, 4 of 4 The range for main-sequence stars is

between 0.08 and 100 solar masses High-mass stars are extremely rare Therefore, stars can range from

8/100 the mass of our Sun to 100 times the mass of our Sun

Star Color = Star TemperatureO

B

A

F

G

K

M

Sun

"We are made of star stuff. We are a way that the cosmos can know itself." -----Carl Sagan in the opening sequence of Cosmos