ASTR Midterm 3

An astronomer wants to observe a cloud of cold neutral hydrogen, far away from any other stars, what should he use to observe it?

A radio telescope, tuned to a wavelength of about 21 centimeters

Many names used by astronomers are misleading or outdated. A good example is the term planetary nebula, which astronomers use to refer to:

A region of gas or dust where new planets have been recently formed.

an HII region is

A zone around a hot star where hydrogen atoms are ionized

Why are astronomers so interested in the luminosity in the stars?

Because it can be used to obtain the distance to the star

If an astronomer wants to find the distance to the main sequence star which is not variable and is located too far away for parallax measurements, they can use:

Find the star's luminosity/surface color and find it on the H-R Chart

When a member of a binary star system is a black hole, and astronomers detect x-rays coming from the system where are the x-rays coming from?

From a disk of material around the black hole which has been pulled from the companion star and is falling towards the black hole

The most stable element in the universe is

Iron

After the core of a star becomes a neutron star the rest of the stars material:

Makes a planetary nebula, which gently moves outward from the center

Two clues dust is blocking starlight

Only Red is visible making stars dimmer,

How to find planet around a star

Periodically measure the doppler shift and see where it changes from planetary pull

The parallax of a star is

The angle a star shifts when seen from opposite sides of the Earth's orbit

What is not true about the interstellar medium?

The density of molecular clouds is similar to the density of a sun-like star

The region inside a black hole where even light may not escape is called:

The event horizon

A supernova is:

The explosion of a star when the iron becomes a part of the fusion process

The event in the life of a star that begins its expansion into a giant is

The hydrogen in its core has been used and only helium is present

In Cepheid variable stars the average luminosity was related to:

The length of time or period they took to vary

When sun expands

it becomes a red giant, moves to top right on H-R chart

Astronomers classify the birth of a star by

when fusion starts to occur inside the star's core