Why does the sun keep burning bright? Take the quiz!


The sun. It's the prime source of energy for all living things on Earth. So how much do you know about this vital celestial body? What causes it to burn brightly for millions of years? Take this quiz to see how much you know about our "day star."

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Question 1 of 20

The sun is primarily composed of hydrogen and _________.


... The sun is 92.1 percent hydrogen, 7.8 percent helium. The rest is mostly oxygen, with other elements such as carbon, neon and nitrogen.


Question 2 of 20

How much of the solar system's total mass is represented by the sun?

25 percent
50 percent
75 percent
more than 99 percent

... More than 99 percent of the mass of our entire solar system is contained in the sun. Of the remaining celestial bodies in the system, Jupiter has the greatest mass.


Question 3 of 20

A solar flare is caused by variations in the sun's __________.

hydrogen levels
magnetic energy

... When magnetism has accumulated in the atmosphere of the sun, it is released rapidly in a solar flare.


Question 4 of 20

How much longer is it estimated that the sun will burn?

500,000 years
5 million years
5 billion years
5 trillion years.

... The sun originally had enough energy to burn for 10 billion years. Since it's almost 5 billion years old, it has about 5 billion years left.


Question 5 of 20

Which of the following is the hottest: the sun's _______?


... While the surface of the sun is about 5,000 degrees F (2,760 degrees C), the outermost atmospheric layer, the corona, is more than 1 million degrees F (555,000 degrees C). The extreme heat of the corona is thought to be caused by magnetic fields.


Question 6 of 20

In the 1930s, British astronomer and Royal Society member John Hershel used solar power to _______.

cook food
heat a greenhouse
light a room
run a car

... Hershel pioneered the use of a "solar thermal collector box" to cook meals on a trip to Africa.


Question 7 of 20

In Earth time, about how long does it take for the sun to make one complete rotation?

one hour
24 hours
it varies
the sun is relatively motionless and does not rotate.

... Since the sun is gaseous, not solid, the entire star does not spin at the same rate, so it will vary. Rotation at its equator takes 27 days, but the poles take 31 days.


Question 8 of 20

Why do sunspots appear darker than the rest of the sun?

They are hotter.
They are colder.
There is more radiation.
There is less radiation.

... At about 6,300 degrees F (3,482 degrees C), sunspots are relatively cool, compared to the areas surrounding them, which are about 10,000 degrees F (5,538 degrees C).


Question 9 of 20

What type of star is our sun?

brown dwarf
red giant
yellow dwarf

... The sun is currently a mid-sized star: a yellow dwarf. As it burns more fuel it will become a red giant and then a white dwarf.


Question 10 of 20

If you could fly to the sun in a jet airliner, it would take _________.

eight years
17 years
88 years
one light year

... Flying at 1,000 kilometers an hour (621 miles an hour), a jet would travel for 18 years until it reached the sun.


Question 11 of 20

What is the energy source for the sun?

nuclear decay
nuclear fission
nuclear fusion
nuclear radiation

... Nuclear fusion takes place in the core of the sun, where hydrogen is changed to helium and energy.


Question 12 of 20

A scientific formula that can be used to explain the sun's tremendous energy was determined by _________.


... Einstein's famous formula E = mc2 (energy equals mass times the speed of light squared) revealed how even a small amount of matter -- in the sun's case, its supply of hydrogen -- can be transformed into an incredible amount of energy.


Question 13 of 20

About how many Earths could fit inside the sun?

more than 1 million

... About 1.3 million Earths could would equal the volume of the sun.


Question 14 of 20

How long does it take light from the sun to reach Earth?

six seconds
eight minutes
five hours
two days

... It takes eight minutes for light to travel from sun to Earth. The light is traveling at more than 186,000 miles per second; it has to span a distance of about 93 million miles.


Question 15 of 20

What does the sun orbit?

the center of the solar system's mass
the center of the universe's mass
the sun does not orbit

... The sun and all the planets in our solar system orbit the center of mass of our solar system. This is located a relatively small distance from the sun. Because the sun's motion is, therefore, so slight, it is often ignored. Our entire solar system also orbits the center of the Milky Way.


Question 16 of 20

The outermost part of the sun's atmosphere can only be seen from space or during a _______.

binary star eclipse
lunar eclipse
solar eclipse
the corona can never be seen from earth.

... During a solar eclipse, when the surface of the sun is blocked by the moon, the corona is visible around the edges of what we see as a dark circle.


Question 17 of 20

What can solar winds affect?

planetary magnetic fields
all of the above

... Solar winds, traveling about 1 million miles per hour (1.6 million kilometers per hour), can affect the direction of a comet's tail, a planet's magnetic field and the course of spacecraft.


Question 18 of 20

Sunspots occur in cycles that last ________.

three years
seven years
11 years
15 years

... Sunspots move through 11-year cycles of ebbing and flowing activity. It is possible the cycles are caused by variations in the magnetic field or moving gases.


Question 19 of 20

The part of the sun that we normally see is called the ________.

radiative zone

... When we look at the sun, we usually see the photosphere. It is the lowest section of the atmosphere, closest to the sun's interior.


Question 20 of 20

What is the size of the average sunspot?

the size of New York
the size of Texas
the size of China
the size of Earth

... Although sunspots can vary in diameter size (from hundreds of miles/kilometers to tens of thousands of miles/kilometers), the average sunspot is the size of our whole planet.


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