Mizar is one of history’s most significant stars


As I taught my very last class at Ohio Wesleyan a few days ago and sat down to work on this column, I realized with a start that I have been writing it weekly since February 1987. That’s 450-plus columns and counting.

Readers sometimes ask me how I’ve managed to do it for so long. The answer is simple — the universe is a vast and fascinating place. Every star has its story.

Last week, we began to discuss the history of one of astronomy’s most famous and storied star systems, Mizar and Alcor.

Here’s part two.

Mizar is the bright star at the bend of the handle of the Big Dipper. Hovering nearby is the much fainter Alcor. At about 83 light years away, they form the Horse (Mizar) and its Rider (Alcor).

Mizar, the brighter star of the two, is one of history’s most significant stars. In 1617, soon after Galileo first used a telescope for astronomy, Benedetto Castelli used his small ‘scope to discover that Mizar is, in fact, two stars. Although no one knew it then, he was the first to see a gravitationally bound stellar system, a binary star.

True to their penchant for giving stars clever names, modern astronomers call the stars Mizar A and Mizar B. They are very young and thus rich in the hydrogen that fuels their thermonuclear reaction.

They are just a hair’s breadth from each other in cosmic terms. Separated by 36 billion miles, they are only 10 times as far from each other as Pluto is from the sun.

Modern astronomers have discovered that Mizar A has a faint companion. It orbits Mizar A in only 20.5 days.

Mizar B also turns out to be a star system with two components. Thus, the Mizar system comprises four stars orbiting each other in a complex pattern. Sadly, only two stars, A and B, can be resolved in an amateur telescope. Mizar is consequently an incredibly complex multiple-star system.

But there’s more. In 2009, a team of astronomers from the University of Arizona discovered that Alcor has a dim, red dwarf companion as well.

But what of Alcor and Mizar? As it turns out, Alcor and Mizar orbit each other like two thumbs engaged in a cosmic twiddle, with a single twiddle taking as much as 750,000 thousand years.

The stars are gravitationally mated for the long haul, a condition represented in an old Indian myth about the two stars.

In Indian philosophy, the seven stars of the big Dipper represent the seven Saptarishi, the authors of many profound Indian philosophical and religious texts.

They were honored with the title “rishi,” the wisest of all the great Indian thinkers. Mizar denotes the sage Vasishtha, one of those rishis.

Alcor represents Arundhati, Vasishtha’s devoted spouse. How devoted are they to each other? One indication might be the 100 children they had together.

The ancient Indian writers couldn’t have guessed that Alcor and Mizar were gravitationally bound. But they did recognize that the two stars traveled the sky together.

They thus represent the inseparability that a couple bound in marriage should aspire to. In the traditional Indian marriage ceremony, the paramours show each other Alcor and Mizar as a loving indication of the permanence of their relationship.

Modern science reveals a much more complex relationship. Alcor’s dim companion orbits Alcor. Meanwhile, the four stars of Mizar also orbit each other in a complex astronomical dance. The Alcor duo and the whole Mizar mess orbit each other. The entire thing resembles a zany, slow-motion teacups ride at some cosmic county fair.

Astronomers have discovered many such multiple-star systems. Most stars are associated in pairs or groups of three or more.

Our daystar star, the sun, turns out to be a celestial oddity, a single star floating in majestic isolation, alone in the vastness of space.

Orbiting that lonely star is a speck of rock. You and I are on that speck, contemplating these things.

Consider that last fact alone, dear readers, and you will understand how a schlub like me can spend a lifetime focused on the pleasures, both educational and inspirational, the nighttime sky has to offer.

Indeed, one lifetime is not enough. My fondest hope is that others will continue that quest after I am gone and that my weekly writing efforts had something to do with it.

Tom Burns is the former director of the Perkins Observatory in Delaware.

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