My Very Cool ASTR A104 EXAM Study Guide

Why do sunspots look dark?

Because it is cooler than its surroundings

Suppose you want to search for brown dwarfs using a space telescope. Which telescope? Why?

Brown dwarfs are very hard to observe because of the cool temperatures and faintness. To search for brown dwarfs you would need to design your telescope to detect light in the infrared part of the spectrum because they put out most of their light in infrared.

If the "fuel" for nuclear fusion is nuclei of hydrogen, and the Earth's oceans are filled with hydrogen atoms in water all being jostled together, why isn't there a lot of fusion happening in our oceans?

For hydrogen nuclei to fuse, they must get very close to each other, which the nuclei in the ocean cannot do.

What is a planetary nebula? Will we have one around the Sun?

It is the final stage of stellar evolution. It is a expanding shell of illuminated gas that surrounds dying low-mass stars. Yes the Sun will have one.

Why can't we use visible light telescopes to study molecular clouds where stars and planets form?

Molecular clouds are very cold, meaning that it is too cold to emit any visible light wavelengths. The visible light can also be blocked by the dust that is surrounding/protecting the molecules. We can't use visible light telescopes because no visible light escapes. Infrared/radio telescopes work better because the cold can emit infrared and radio light, and because they are less likely to be blocked by the dust in the molecular cloud.

Put smallest to largest: Supernova remnant 500 yrs after explosion, Sun, Neutron star, Red giant star, White dwarf

Neutron Star, White dwarf, Sun, Red Giant Star, Supernova remnant 500 yrs after explosion

Are positrons a fundamental particle that we can find inside atoms?

No lol

Are helium and hydrogen classified (under astronomer terms) as metals?

Nooooooooo

Why is our Sun not collapsing under its tremendous gravity?

Nuclear fusion in the core keeps the temperature and the pressure inside the Sun at a high enough level so that gravity is balanced.

Evolutionary cycle of a low-mass star in chronological order:

Prostar, Main sequence, Red giant, Planetary Nebula, White Dwarf

T OR F: Closest star to Earth is Proxima Centarui.

T

T or F: When a star dies as a supernova, more material explodes outward than remains in the part of the star that is left behind.

TRUE

Which part of the Sun has the greatest density?

The core

The Sun's surface appears sharp when viewed from Earth because

The photosphere is thin compared to the Sun's size

Two protostars, one 10 times the mass of the Sun and one half the mass of the Sun are born at the same time in a molecular cloud. Which one will be first to reach the main sequence stage, where it is stable and getting energy from fusion?

The star that is 10 times the mass of the Sun. This is because the more massive a star is, the faster it will become a protostar that is stable and gets energy from fusion.

What do measurements of the number of neutrinos emitted by the Sun tell us about conditions deep in the solar interior?

Through the neutrinos we can explain the Sun's energy output.

How do astronomers know what the outer layer of the Sun are made of?

We take absorption line spectrum of the Sun, which tells us what elements are present.

What is the Orion Nebula?

a large cloud of gas and dust illuminated by the light of newly formed stars within it

According to the formula E=mc2, what?

a little bit of mass can be converted into a substantial amount of energy

What is a way astronomers have to find white dwarfs that distinguishes them from main sequence stars?

because white dwarfs get really hot, we can search for their ultraviolet radiation

Really massive stars differ from stars with masses like the Sun in that they

can fuse elements beyond carbon and oxygen in their hot central regions

Above photosphere is a region of thinner, hot gas, called the

chromosphere

Above the radiative zone is a region where vast bubbles of hot material move up then sink down, called the

convective zone

The innermost part of the Sun is called its

core

The sun's outermost layer is called the _____, and has very low density

corona

The granulation pattern that astronomers have observed on the surface of the Sun tells us that:

hot material must be rising from the Sun's hotter interior

When an astronomer describes the luminosity of a star she is studying, she is talking about:

how much energy the star gives off each second

The most common element in the Sun is

hydrogen

Studies of the spectra of stars have revealed that the element that makes up the largest part of each star is

hydrogen (75% mass)

The transit technique has a particular selection bias making it most easily able to specifically detect

large-diameter planets

When energy is produced and released by the Sun's core, it leaves the core in the form of

photons

The layer where the sun becomes opaque and we cannot see further is called its

photosphere

Above the core is a region where the energy moves very slowly bc the mattery is densely packed; this is called the

radiative zone

What kind of telescope did Jocelyn Bell use to discover pulsars in 1968?

radio

Why can astronomers not measure the diameters of stars directly

stars are far away (obviously)

Astronomers believe that the many supernova explosions that happened in the Milky Way Galaxy could have played a role in the evolution of life over billions of years? How would they have influenced the development of life on Earth?

the cosmic rays produced by supernova explosions would have contributed to the rate of mutations over many generations

How can we explain behavior of the non-shifting lines?

the lines come from interstellar matter between us and the star, not from the star itself

Ninety percent of all stars (if plotted on an H-R diagram) would fall into a region astronomers call:

the main sequence

The Doppler Shift

the shift to a different wavelength on the electromagnetic spectrum

What would allow a nova explosion to happen to a star more than once?

the star that goes nova has a companion near it, which dumps material onto the first star and continues to do so even after the first nova explosion.

When the core of a star reaches temperature of about 100 million degrees (K), something new happens in the core. What?

three helium nuclei begin fusing carbon

Astronomers identify the "birth" of a real star with what activity in the star?

when nuclear fusion reactions begin inside its core