Astronomy Final

We see many sunspots on the surface of the sun. Solar max is when the sun is most active, so there are more solar flares.

4 H --> 1 He + energy.

The core would expand, reducing the pressure and temperature, and the rate of fusion would decrease until it returned to its original level.

They actually are fairly bright, but appear dark against the even brighter background of the surrounding photosphere.

As the Sun was forming, gravitational contraction increased the Sun's temperature until the core become hot enough for nuclear fusion, which ever since has generated the heat that makes the Sun shine.

Earth's upper atmosphere tends to expand during solar maximum, exerting drag on satellites in low orbits.

The Sun generates energy by fusing small nuclei into larger ones, while our power plants generate energy by the fission (splitting) of large nuclei.

The chromosphere is best observed with ultraviolet telescopes and the corona is best observed with X-ray telescopes.

We can send a space probe into the Sun's photosphere.

Fusion in the Sun's core creates neutrinos as a byproduct.

5,800 K

There is a balance within the Sun between the outward push of pressure and the inward pull of gravity. Every second, the Sun converts 600 million tons of hydrogen into 596 million tons of helium. The remaining 4 million tons are converted to an amount of energy equal to 4 million tons times the speed of light squared.

It predicted that the Sun could shine for about 25 million years, but geologists had already found that Earth is much older than this.

Experimental evidence suggests that solar neutrinos can change from electron neutrinos to other types of neutrinos during their journey to Earth. If confirmed, the solar neutrino problem appears to be solved.

extremely hot plasma flowing along magnetic field lines.

It was important when the Sun was forming from a shrinking interstellar cloud of gas.

Nuclei normally repel because they are all positively charged, and can be made to stick only when brought close enough for the strong force to take hold.

We are seeing hot gas rising and cool gas falling due to the convection that occurs beneath the surface.

The sunspot cycle is very steady, so that each 11-year cycle is nearly identical to every other 11-year cycle

by looking for the splitting of spectral lines in the Sun's spectrum

millions of degrees.

core, radiation zone, convection zone, photosphere, chromosphere, corona

They have a tendency to pass through just about any material without any interactions.

nuclear fusion

Neutrinos rarely, if ever, interact with your computer.

10 million K

10 million years

C

Open and globular clusters each typically contain a few hundred stars.

10 parsecs.

- All of these are true. - A star with apparent magnitude 1 is brighter than one with apparent magnitude 2. - The magnitude system that we use now is based on a system used by the ancient Greeks over 2,000 years ago that classified stars by how bright they appeared. - A star's absolute magnitude is the apparent magnitude it would have if it were at a distance of 10 parsecs from Earth. - The absolute magnitude of a star is another measure of its luminosity.

larger than that of Star B.

The diagram shows main-sequence stars of every spectral type except O, along with a few giants and supergiants.

They generate energy through hydrogen fusion in their core.

20 parsecs away.

In order to measure the total apparent brightness of a star, you must measure its brightness in all wavelengths, and this is difficult to do. The only wavelengths you can measure from the surface of Earth are visible and radio wavelengths.

G

three quarters hydrogen, one quarter helium, no more than 2% heavier elements

orbital period and average orbital distance.

by converting hydrogen to helium.

remains the same, but the apparent brightness is decreased by a factor of four.

the galaxy's bulge

Halo stars formed in an environment where there were few heavy elements to create rocky planets.

The stars that formed first could orbit the center of the galaxy in any direction at any inclination.

very old.

by observing in high-energy wavelengths such as X-rays and long wavelengths of light such as radio waves

Sagittarius

a very low-density region of interstellar space, formed by the merger of several bubbles

The total amount of gas will be much less than it is today.

Globular cluster ages increase with distance from the Milky Way.

have a greater abundance of heavy elements.

The orbits of stars in the center of the galaxy indicate that the presence of 3- to 4-million-solar-mass object in a region no larger than our Solar System.

It is probably a halo star that is currently passing through the disk.

as a flattened disk with a central bulge and barred-spiral arms.

warm, rarefied clouds of atomic hydrogen

There are no blue halo stars.

He proved this by observing individual Cepheid variable stars in Andromeda and applying the period-luminosity relation.

away from us at 2,000 km/s

14 billion years.

all but irregulars

velocity and distance

32,500 km/s

100 billion.

It would mean the distance to the Andromeda Galaxy is also 10% greater than we thought.

stellar parallax

the galaxies that are farthest away

Cepheids are pulsating variable stars, and their pulsation periods are directly related to their true luminosities. Hence, we can use Cepheids as "standard candles" for distance measurements.

the period between its peaks of brightness and its luminosity

less than a billion

- They are very bright, so they can be used to determine the distances to galaxies billions of light-years away. - They should all have approximately the same luminosity.

the expansion of the universe.

The orbital speeds of stars far from the galactic center are surprisingly high, suggesting that these stars are feeling gravitational effects from unseen matter in the halo.

measuring the temperatures of stars in the halos of the galaxies

the repulsive agent causing the universal expansion to accelerate

the higher the amount of mass relative to light (higher mass-to-light ratio), the greater the proportion of dark matter.

dark matter represents much more mass and extends much further from the galactic center than the visible stars of the Milky Way.

Yes, they tell us that dark matter is spread throughout the galaxy, with most located at large distances from the galactic center.

the expansion of the universe

Gas clouds orbiting far from the galactic center have approximately the same orbital speed as gas clouds located further inward.

It consists of atoms or ions with nuclei made from protons and neutrons.

The measurements show that the expansion is accelerating, rather than slowing under the influence of gravity.

It emits no or very little radiation of any wavelength.

by using the position on the sky and the redshift to determine a distance along the line of sight

It is a name given to whatever is causing the expansion of the universe to accelerate with time.

Using Einstein's general theory of relativity, we can calculate the cluster's mass from the precise way in which it distorts the light of galaxies behind it.

They respond to the weak force but not to the electromagnetic force, which means they cannot emit light.