Lesson 8: Stars, clusters, and star colors

Stars stay tiny points of light, even in the biggest telescopes. They're that far away. Your telescope still shows you plenty, like star colors, star pairs, and crowds of stars.

Star colors tell temperature

Look closely and you'll see that stars have colors. A star's color tells you how hot its surface is. Something heated glows red first, then orange, yellow, and white as it gets hotter. Stars follow the same pattern, and the hottest ones glow blue-white.

Orion, the Hunter. Betelgeuse glows at the top left and Rigel at the bottom right.

Image: Rogelio Bernal Andreo, CC BY-SA 3.0 · Source

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Orion, the Hunter, shows off two colors. He climbs high on winter evenings. Betelgeuse, at his top left, glows orange-red. Rigel, at his bottom right, glows blue-white.

Betelgeuse, a red supergiant star, imaged by the European Southern Observatory.

Image: ESO/P. Kervella, CC BY 4.0 · Source

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Betelgeuse

A red supergiant, one of the coolest bright stars you can see.

Image: ESO/P. Kervella, CC BY 4.0

The Sun, a yellow-white star.

Image: NASA/SDO, ALMA (ESO/NAOJ/NRAO), CC BY 4.0 · Source

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The Sun

Our own star, yellow-white and in the middle of the range.

Image: NASA/SDO, ALMA (ESO/NAOJ/NRAO), CC BY 4.0

Rigel shines blue-white beside the Witch Head Nebula.

Photo: Giuseppe Donatiello · Source

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Rigel

A blue-white star, far hotter than the Sun.

Photo: Giuseppe Donatiello

Double stars

Many stars that look like one star to your eyes are two stars close together. In some pairs, the two stars orbit each other.

Mizar, the double star on the right, and Alcor, on the left.

Image: Nikolay Nikolov, CC BY-SA 4.0 · Source

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Mizar and Alcor

The middle star in the Big Dipper's handle is Mizar. Look closely and you may see a faint partner beside it, Alcor. Point your telescope at Mizar and it splits into two more stars.

Image: Nikolay Nikolov, CC BY-SA 4.0

Albireo through an 8-inch telescope. One star glows gold and the other blue.

Image: Topoignaz, CC BY-SA 4.0 · Source

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Albireo

On summer and fall evenings, find Albireo at the head of Cygnus, the Swan. Your telescope splits it into a gold star and a blue star. It's a favorite of astronomers.

Image: Topoignaz, CC BY-SA 4.0

Star clusters

A star cluster is a family of stars that formed together from the same cloud of gas and dust.

The Pleiades, also called the Seven Sisters, look like a tiny dipper made of blue-white stars. They climb high on fall and winter nights. Your eyes see about six stars there. Your telescope at low power shows dozens.

The Pleiades, also called the Seven Sisters.

Photo: NASA, ESA, AURA/Caltech, Palomar Observatory · Source

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Use your lowest power eyepiece for clusters. They spread across a lot of sky, so they need a wide view.

A star nursery

Below Orion's Belt hangs a short line of stars called his sword. The middle star of the sword looks fuzzy. It's the Orion Nebula, a giant cloud of gas and dust where new stars are forming, about 1,300 light-years away.

A light-year is the distance light travels in one year, about 6 trillion miles. The light you see from the Orion Nebula left it about 1,300 years ago.

The Orion Nebula, a star nursery, photographed by the Hubble Space Telescope.

Photo: NASA, ESA, M. Robberto (STScI/ESA) and the Hubble Orion Treasury Project Team · Source

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