Astronomy 103 Problem Set 5

When hydrogen fuses to helium, what fraction of its mass changes to energy?

0.7% (people are often unclear on this, mistakenly thinking that the entire mass of the initial hydrogen is changed into energy)

About how hot is the Sun's core?

1.5 x 107 K

The time between one sunspot maximum and the next one is about...

11 years

How many times more massive is the Sun than the Earth?

300,000

If 6 kg of mass is changed entirely into energy, how much energy is produced?

5.4e+17 because the energy produced by converting a mass m of matter entirely to energy is given byE = mc2. With m in kg and the speed of light in m/s (c=3x108m/s),the energy is given in watt-s

How much energy does a 100-watt light bulb emit in one minute? Give the answer as a number of watt-seconds.

6000

About how hot is the Sun's photosphere?

6000 K

If a star turns 1025 kg of matter into energy in one second, how much energy does it produce in that second?

9x1041 watt-seconds

The density of the Sun is closest to that of which of the objects listed below?

A comet because comets are made of ice, and their density is about the density of water, close to the Sun's density.

T/F Neutrinos have never been detected experimentally.

False

T/F Sunspots appear dark because they are hotter than the surrounding gas of the photosphere.

False

T/F The proton-proton chain releases energy because mass is created in the process.

False

T/F There are as many absorption lines in the solar spectrum as there are elements present in the Sun.

False

T/F The density and temperature in the solar corona are much higher than in the photosphere.

False because the corona is hotter, heated up by magnetic storms above the photosphere. But the Sun's density decreases from center to the outside, and the corona has very little material. The photosphere is much denser.

The primary source of the Sun's energy is...

Fusion of light nuclei to make heavier ones

The Sun is a stable star in which...

Gravity balances the force from pressure because the energy emitted by the core ultimately leaves the Sun, mostly as visible light. It is not absorbed by the nearly transparent corona.

The Sun's energy is produced by the fusion of...

Hydrogen to helium

The Sun spins on its axis roughly once each...

Month

Compared with Earth's diameter, the Sun's diameter is about...

One hundred times larger

The visible light we see from the Sun comes from what part of the Sun?

Photosphere

T/F The most abundant element in the Sun is hydrogen.

True

The density of the Sun is closest to the density of...

Water because the gas between stars is extremely sparse. The space between stars is a much better vacuum than the best vacuum we can create on Earth.

Spica, the brightest star in the constellation Virgo, has luminosity 8x1029watt. How much mass does it change to energy each second? Give the answer in kg to two significant figures. (ex. problem)

~8,888,888,888,889 because this uses m = E/c2 . The energy Spica produces in one second is 9x1029 watt-seconds. With c = 3x108 m/s, the mass is given in kg.