Return of the Speed Quiz

How do we measure stellar luminosities?  If we measure a star’s apparent brightness and distance, we can compute its luminosity w/ the inverse square law for light.  Parallax tells us distances

to the nearest stars.

How do we measure stellar temperatures?  A star’s color and spectral type both reflect its temperature.

How do we measure stellar masses?  Newton’s version of Kepler’s 3rd law tells us the total mass of a binary sys. If we can measure the orbital period (p) and avg. orbital separation of the sys (a).

P^2 = ((4x^2)/G(M1+M2))*a^3

How do we measure the age of a star cluster?  A star cluster’s age roughly equals the life expectancy of its most massive stars still on the main sequence.

How do stars form?  Stars are born in cold, relatively dense molecular clouds.  As a cloud fragment collapses under gravity, it becomes a protostar surrounded by a spinning disk of gas.  The

protostar may also fire jets of matter outward along its poles.

How massive are new born stars?  Stars greater than about 150M sun would be so luminous that radiation pressure would blow them apart.  Degeneracy pressure stops the contraction of

objects <0.08M sun before fusion starts.

How does a low-mass star die?  Ejection of H and He in a planetary nebula (and eventually galactic gas) leaves behind an inert white dwarf.

How does a star’s mass determine its life story?  Mass determines how high a star’s core temperature can rise and therefore determines how quickly a star uses its fuel and what kinds of

elements it can make.

How is gas recycled in our galaxy?  Gas from dying stars mix new elements into the interstellar medium which slowly cools, eventually creating molecular clouds where new stars form.

Those stars will eventually return much of their matter to interstellar space.

How does inflation explain these features? (see “What aspects of universe… question)  Structure comes from inflated quantum ripples.  Inflation flattened the curvature of space, bringing

the expansion to rate into balance with the overall density of mass-energy.

How can we test the idea of inflation?  We can compare the structures we see in detailed observations of the microwave background w/ predictions for the “seeds” that should have been planted by inflations.  So far, our

observations of the Universe agree w/ models in which inflation planted the “seeds”.

How do we observe the radiation left over from the Big Bang?  Radiation left over from the Big Bang is now in the form of microwaves- the cosmic microwave background, which we can

observe w/ a radio telescope.

How do the abundances of elements support the Big Bang Theory?  Observations of helium and other light elements agree w/ the predictions for fusion in the theory.

How did life arise on Earth?  Life evolved from a common organism through natural selection, but we do not yet know the origin of the first organism

How many civilizations are out there?  We don’t know, but the Drake equation gives us a framework for thinking about the question.

How does SETI work?  Some telescopes are looking for deliberate communications from other worlds.

How many He nuclei fuse to make C? 3

Pluto is different from the Jovian planets in all of the following ways except which one? It’s surface temperature is very cold

The Sun’s habitable zone extends from some place a little beyond the orbit of Venus to some place near the orbit of Mars.

These 2 stars have about the same luminosity- which is brighter- Alpha Centauri or Sun?  Sun – we judge by apparent brightness, so Sun is brighter.

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