Stars

What are stars?

A star is a giant ball of hot, glowing gases (mostly hydrogen) that release energy.

Some of the energy is in the form of light.

Some of the energy is in the form of heat (thermal energy).

All stars, except for our sun, look like tiny dots of light because
they are very far away.

Light from stars

• Light from stars takes time to

reach Earth.

• Light travels at 300,000 kilometers

per second (about 186,411 miles
per second).

• The distance light travels from

stars is measured in light-years.

• A light-year is the distance light

travels in one year.

Star brightness and
distance

• When it is viewed from Earth, our

sun appears to be a very bright
star relative to (compared with)
other stars.

• This is because our sun is the

closest star to Earth.

• A star’s actual brightness and its

apparent brightness can be very
different depending on distance,
how hot the star is, etc.

Types of stars

Our sun and most stars in the

universe are similar in many ways, but

they also differ in some ways.

Stars can be different sizes, have
different colors, and have different

temperatures.

Star colors and
temperatures

• A star’s color is a result of its temperature.

• Colors include red, orange, yellow, white,

and blue.

• As you move from the colors on the

left to the colors on the right, the
temperature increases.

• For example, a red star is the coolest

and a blue star is the hottest.

• An orange star would be hotter than

a red star, but cooler than a yellow
star, and so on.

How can we better detect
stars?

• Telescope 🡪 A telescope is a tool that

makes distant objects appear closer,
large, and easier to see. There are
several different types.

• Refracting 🡪 Use lenses to collect and

magnify visible light.

• Radio 🡪 Detect radio waves to find

objects in space that cannot be seen
by optical telescopes.

• Optical 🡪 Use lenses to gather,

magnify, and focus light.

• Reflecting 🡪 Use mirrors to see

objects in the sky.

• The Hubble Space Telescope &

The Keck Observatory’s twin
telescopes.