Is red Antares bigger than our sun?

Antares is a red supergiant star, and, yes: it is much bigger than our sun (some 700 times our sun’s diameter). If placed in the center of our solar system, Antares’ outer surface would lie between the orbits of Mars and Jupiter!

This star is the brightest member of a collection of stars sometimes called the Local Star Cloud. Other stars visible each evening now also belong to this group. These stars were born less than 20 million years ago.

A star’s mass determines the rate of its evolution – and Antares alone in its family of stars has evolved to become a red giant. In other words, as it aged, it ballooned in size. Our sun will also become a red giant, someday. Astronomers see many other red giants scattered through the space of our Milky Way galaxy.

The ancients saw red Antares as the ruby Heart of the Scorpion in the constellation Scorpius. This star lies on the Zodiac – also traveled by the sun, moon, and other planets – and the ancient stargazers considered it a rival to the red planet Mars. In fact the name Antares or Ant-Ares means like Mars (Ares is the Greek name for the god of war).

Antares’ season is summer. It shines on summer evenings, high in the south as seen from the northern hemisphere. Early stargazers knew Antares as one of four Royal Stars. Each of these four is prominent in a different season.

Try looking at Antares with binoculars. Near it, you’ll see a round fuzzy ball – a globular cluster called M4. This cluster is located some 15 thousand light-years away – and contains hundreds of thousands of stars.

September 15, 2009

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