If not for its location, the star Megrez would attract little attention. It doesn’t look especially bright, and while the star itself is bigger and brighter than the Sun, it’s still not all that remarkable.
Yet we do pay attention to the star, because it’s a celestial thumbtack — it connects the bowl and handle of the Big Dipper.
In astronomical parlance, Megrez is a class A3 dwarf. The “A3” part of that designation means its surface is thousands of degrees hotter than the Sun’s, so it shines pure white. And the “dwarf” part means that it’s in the prime of life, steadily converting the hydrogen in its core to helium. A star in that phase of life isn’t exactly tiny — Megrez is a couple of million miles in diameter. But later in life, it will puff up to many times that size — it’ll be not a dwarf, but a stellar giant.
Megrez and four other members of the Big Dipper are siblings — they were born from the same cloud of gas and dust, and they move through space together. The other Dipper stars in the group are the two at the bottom of the bowl, and the two in the handle that are closest to Megrez. They’re all about 80 light-years from Earth.
The Big Dipper is high overhead as night falls, with the handle to the right of the bowl, linked by Megrez. It’s the faintest star in the entire dipper, but perhaps the most important: Without it, there would be no Big Dipper at all.
We’ll talk about another star in the Big Dipper tomorrow.
Script by Damond Benningfield