OK, I admit I may not remember where my car is parked, but I sure recall my grade school planetarium field trips like they just occurred.
These were some of the highlights of my youth, and they played a huge role in my decades-long career as a planetarium astronomer.
It was great fun seeing the stars and constellations projected onto the overhead dome while the lecturer pointed them out and told stories about those visible that night.
Equally enjoyable — at least for me — was to race outdoors after dinner to check them all out in the real night sky!
One of my favorite star groupings of springtime was the Big Dipper. This group of seven stars is part of a larger constellation known as Ursa Major, the Great Bear, but tracing a bear is not for impatient stargazers.
From my backyard, I could always count on the Dipper to be hovering over my house to the north. But what I learned from the planetarium was how to use the Dipper to find other stars in the sky.
Of course, its “pointer stars” direct us to Polaris and other stars, something I’ve written about recently.
But I remember one planetarium show when the astronomer showed even more. He traced the curving arc of the Dipper’s handle away from its bowl and demonstrated how to find two even brighter stars.
I remember he said, “Just follow this arc toward Arcturus … then speed on to Spica.” Well, that was pretty cool, and that evening, I was able to do exactly that.
Equally fun, though, was learning a bit about each of these two stars.
Yellowish-orange Arcturus is the fourth-brightest star in all the heavens and lies only about 37 light years from us. It’s an immense star — a red giant, we call it — about 25 times larger, and about 170 times more radiant, than our sun.
Arcturus was one of the first stars ever to receive a proper name.
In ancient times, it was known as the “Watcher” or the “Guardian”; Arab stargazers knew it by two names, which translate as “the Lance-Bearer” and “the Keeper of Heaven.”
Today, we use a name that comes from the ancient Greek word Arktouros, meaning “Bear Guard”; quite appropriate since it never strays from the great celestial bear.
Nearby, bluish-white Spica is estimated to lie about 250 light years from Earth, but it’s not just a single star.
The light we see from Spica comes from the combined light of two stars that orbit one another every four days. Together they produce about 12,100 times more luminosity than the sun.
Spica was an important star in ancient days too. Around 3,200 B.C., the temple at Thebes was oriented to Spica and, in the second century B.C., Hipparchus used the star to discover the wobble of the Earth’s axis (known as precession).
If you’re not sure you’ve found Spica, the waxing gibbous moon will help on May 10, when it will appear nearby.
The Dipper, Arcturus and Spica will appear higher in the sky each evening for the next few months and will offer a beautiful sight all spring and summer.
