Self Assessment Week 11 (ch 18, 19, & 20)

The comet-hunting astronomer who made a list of over 100 nebulae and galaxies that could be mistaken for comets was

Charles Messier

When astronomers discuss a nebula, what are they talking about?

a giant cloud of gas and dust between or among the stars

The light element lithium (which, on Earth, is part of medications that improve the lives of people with mental health illnesses) is more common in cosmic rays than it is in the Sun and the stars. What do astronomers think is the reason for this?

because cosmic rays move so fast, they can collide with atoms of carbon, nitrogen, and oxygen and break them apart, producing more light elements like lithium

Why can astronomers not tell from what direction a particular cosmic ray started toward the Earth?

cosmic rays are charged particles and are thus spiral around the Earth and the Galaxy's magnetic field

Which of the following statements about interstellar matter is FALSE?

if the matter were spread out evenly, it would be about as dense as the Earth's atmosphere

The closest star to the Sun, Proxima Centauri, was recently found to have a planet in its habitable zone. Proxima Centauri is a main sequence star with spectral type M. How would its habitable zone differ from the habitable zone of our Sun?

it would be significantly closer to Proxima Centauri than ours is to the Sun

An astronomer is observing a single star (and one which does not vary) which she knows is located about 30 light-years away. What was the most likely method she or her colleagues used to obtain that distance?

measuring the star's parallax

A type of star that has turned out to be extremely useful for measuring distances is

the Cepheid variables

You are an astronomy graduate student and you are observing the big Orion Nebula from an airplane that has a good-sized infrared telescope built into it (there really is such a plane.) On an infrared image of the Nebula, what would particularly stand out?

the clouds of the nebula that have a lot of dust in them

Which of the following are the small regions that are the embryos of stars (where individual stars are most likely to be born)?

the cores within the clumps of molecular clouds

Why do Cepheid variables have that strange name?

the first such variable was discovered in a constellation called Cepheus

The higher the luminosity (intrinsic brightness) a Cepheid variable is,

the longer the period of its variations

Astronomers identify the "birth" of a real star (as opposed to the activities of a protostar) with what activity in the star?

when nuclear fusion reactions begin inside its core