Learning Goals: 4. Complex Knowledge: demonstrations of learning that go aboveand above and beyond what was explicitly taught. 3. Knowledge: meeting the learning goals and expectations. 2. Foundational knowledge: simpler procedures, isolated details, vocabulary. 1. Limited knowledge: know very little details but working toward a higher level. How do stars differ from moons and planets, and from one another? How does the classification of stars help us understand how they evolve over their lifetimes? What are the different types of stars? What happens when different types of stars die? Why is it important for us to understand stars?

Bell Work 3-9-16 Why are HR diagrams considered so useful in astronomy?

Types of stars – Luminosity classes symbol Properties Examples Hypergiant Supergiant I Giant III Subgiant IV Main sequence V White dwarf VII

Stars are classified into luminosity classes.

Today’s Question What two factors do we need to know to determine a stars luminosity? How do we determine a stars size, and therefore it’s luminosity?

Basically Temperature of the star Main Sequence Stars follow this pattern. Not all stars do though.

Basically size of the star

How can we tell which class a star belongs to? DENSITY! The higher the Roman Numeral, the MORE DENSE the star How do we tell the density of the star? Spectral lines! (yes, those again) The thinner the lines  the thinner the stars atmosphere  and the less dense the star  so the bigger it is  and the lower the Roman Numeral

An answer to today’s question

Spectral Lines – Where light is absorbed by atoms

Which is the bigger star?

Repeat Bigger stars have are more spread out, and have thinner atmospheres! Which means LESS light is absorbed by that atmosphere So in big stars the absorption lines are skinnier because more light gets through Small stars therefore have thicker absorption lines corresponding to their thicker atmospheres!

Which is the bigger star?

Hypergiants:0  Hypergiants: A hypergiant (luminosity class 0) is a star with an enormous mass and luminosity, showing signs of a very high rate of mass loss. Hypergiants are very rare and they have a short lifespan. While the Sun has a lifespan of around 10 billion years, hypergiants will only exist for a few million years. If our Sun were a human that lived for 70 years, then Hypergiant stars would last less than a month. Could life form on planets around these stars?

Hypergiants are the largest stars in the universe, even larger than supergiants. The largest hypergiant was VY Canis Majoris, which is between 1300 and 1540 times wider than the Sun, or roughly the same diameter as the orbit of Jupiter.

Then we found V354 Cephei, which held the title for a while Then we found V354 Cephei, which held the title for a while. Then came the hypergiant NML Cygni, which is about 1,650 times wider than the Sun.

Then the largest was Westerlund 1 BKS AS Then the largest was Westerlund 1 BKS AS. It is one of the extreme luminous supergiant stars.

Now it is UY Scuti

Supergiants:I (Ia or Ib)  Supergiants: Very massive and luminous stars near the end of their lives. They can also be a or b, a are brighter. These stars are very rare, less than 1 in a million stars is a supergiant. The nearest is Canopus (F0Ib) 310 light years away. Others are Betelgeuse (M2Ib), Rigel (B8Ia), and Antares (M1Ib) .

Giants: II and III Giants: mainly low-mass stars at the end of their lives that have swelled to become a giant star. This category also includes some high mass stars evolving on their way to supergiant status . Some examples are Arcturus (K2III), Hadar (B1III), Pollux (K0III) and Aldebaran (K5III).

Subgiants: IV Subgiants: Stars which have begun evolving to giant or supergiant status. examples are Alnair (B2.5IV) and Muphrid (G0IV). Note also Procyon which is entering this category and therefore is: F5IV-V.

Main Sequence (dwarf): V Main Sequence (dwarf): All normal hydrogen-burning stars. Stars spend most of their lives in this category before evolving up the scale. Class O and B stars in this category are actually very bright and luminous and generally brighter than most Giant stars. examples are the Sun (G2V), Sirius (A1V), and Vega (A0V).

Subdwarf: VI Similar to a main sequence star Fusing Hydrogen into Helium Less luminous than a main sequence star Has more metal Means it is made out of other star’s guts 3rd or 4th or 5th or 6th generation

Subdwarf: VI

White Dwarf:VII White Dwarf: a small object composed mostly of electron-degenerate matter (huh?). They are the very dense cores of past stars (a teaspoon of white dwarf would weigh the same as an elephant); mass is comparable to the Sun and its volume is comparable to Earth. Its faint luminosity comes from the emission of stored thermal energy. This makes them very hot but very faint. Examples are Sirius B and Procyon B

There are other objects that sometimes fail to fit our classification scheme Brown Dwarfs objects which are too large to be called planets and too small to be stars. They have masses that range between twice the mass of Jupiter and the lower mass limit for nuclear reactions (0.08 times the mass of our sun).

Read the article about brown dwarfs. Answer this question in your science journal when you are done Why are brown dwarfs more like stars than planets?

Color  Temperature What two factors do we need to know to determine a stars luminosity? How do we determine a stars size, and therefore it’s luminosity?

Work on the worksheet (2 of 4) It’s due when you walk in tomorrow!

10 100 1000 3000 10000 50000 200000 Mintaka Rigel Sirius Procyon Sun Spectral class Lifetime (millions of years) examples O 10 Mintaka B 100 Rigel A 1000 Sirius F 3000 Procyon G 10000 Sun K 50000 Aldebaran M 200000 Betelgeuse