Observing the sky

There are many billions of stars in the universe. Some of these stars are much, much larger than the Sun. Why don't stars that are larger than the Sun completely light up the Earth's sky?

• These stars are colder than the Sun.

• These stars are much farther away than the Sun is.

• These stars are dark on the side that faces the Earth.

• These stars don't give off as much light as the Sun.

One of the closest stars to Earth is Alpha Centauri A. It is larger than the Sun, yet it appears much less bright. Which of the following is the best explanation for this?

• The smaller a star is, the more concentrated its energy is, so it appears brighter.

• The difference in brightness is due to the difference in relative distance.

• Dust in the Earth’s atmosphere absorbs the light of all the stars we see.

• As stars get older, the amount of light they give off decreases.

How many of the stars, visible in the night sky, are closer to Earth than the Sun?

• All of them

• About half of them

• None of them

• Only one

An astronomer is studying two stars that have about the same size and brightness. From the Earth, one of the stars appears very bright in the night sky. The other star appears very faint and dim.

Why does one star appear to be brighter than the other?

• The Earth is closer to the brighter star.

• The Earth is farther from the brighter star.

• The Earth is moving toward the dimmer star.

• The Earth is moving toward the brighter star.

Which of the following observations would provide evidence to support the explanation for why some stars that are larger than the Sun appear to be less bright?

• A large campfire seen at a distance of 20 feet is not as bright as a candle that is 5 inches away.

• A 100-watt lightbulb is much brighter than a 25-watt bulb, even if both bulbs are exactly the same size.

• Most stars are not visible during the day because the brightness of the Sun is much greater.

• A flashlight appears dimmer if it is covered with different colored lenses that change the color of the light it gives off.

In comparison to other stars in the sky, the Sun appears brighter because it is–

• hotter

• larger

• older

• closer

Data from four different stars is provided in the table.

Based on the information provided, which of the stars will appear the brightest to observers on Earth?

• A

• B

• C

• D

A light year is...

• The speed light travels

• How long it takes light to get to you from the sun

• The distance light can travel in a year

• How many years it takes light to be emitted

Charlie looks into the sky with his telescope. One of the stars he sees is a small dot of light named Vega.

Vega is about twice as wide as the Sun. Why does Vega look so much smaller than the Sun?

• It isn't as hot.

• It is much farther away.

• Its height is much smaller.

• It doesn't give off as much light.

Which statement about the sun and other stars is TRUE?

• The sun is much larger than other stars so it blocks our view of the other stars during daylight hours.

• The sun is much closer to Earth than other stars so its brightness blocks the light from the other stars during daylight hours.

• The sun is about as bright as other stars so the light from other stars is visible during most daylight hours.

• The sun is much closer to Earth than the other stars, but the other stars are visible most daylight hours.