Stars are made of mostly which two gases?

• Hydrogen and Helium

• Hydrogen and Oxygen

• Hydrogen and Nitrogen

• Hydrogen and Carbon

Stars give off heat and light in a process called ___________.

• nuclear fusion

• supernova

• luminosity

• spectroscopy

In the process of nuclear fusion, hydrogen atoms combine to form ___________ atoms.

• helium

• carbon

• nitrogen

• oxygen

Billions of stars are held together in groups called __________.

• galaxies

• solar systems

• planets

• comets

The luminosity of a star describes its ______________.

• brightness

• temperature

• age

• color

What color are the coolest stars?

• red

• blue

• white

• orange

What color are the hottest stars?

• blue

• red

• white

• yellow

Characteristics used to classify stars include

• distance, size, and color.
• size, distance, and brightness.
• color, brightness, and distance.
• size, brightness, and temperature.

Astronomers typically measure distances to stars in units called

• kilometers.
• light-years.
• parallax.
• electromagnetic spectrum.

The brightness of a star as seen from Earth is its 

• apparent brightness.
• absolute brightness.
• parallax.
• reflective brightness.