Occult occurrence: Watch the moon hide the seven sisters
Greetings, fellow star gazers. Make sure to mark Tuesday night, April 8 as the night when a cosmic occult occurrence will occur.
That’s because whenever one object in the heavens passes directly in front of another object and hides it, we call such an event an occultation because the word occult comes from the word "to hide."
And in the early evening of April 8, an exquisite crescent moon complete with earthshine will pass over the fabled star cluster the Seven Sisters and occult them, that is hide them from view for a brief time.
Let me explain.
Just after dark, facing west, you will see an exquisite, three-day old crescent moon complete with earthshine.
In case you’ve forgotten what earthshine is, simply keep in mind that the moon does not make its own light but shines by reflected sunlight. So the bright part of the crescent moon you’ll be seeing is sunlight bouncing directly off the moon and back to Earth.
However, when the moon is a crescent, it frequently looks like there’s a dark full moon nestled within this crescent. And we call this earthshine because it is light from the sun bouncing off our Earth onto the unlit portion of the moon and back again. The crescent moon with earthshine is always a beautiful sight.
But on this night if you look close by you will see several stars bunched up together in a group, the tiny cluster of stars known for thousands of years as the Seven Sisters, the Pleiades. And on this evening, from many places across North America, moon watchers will be able to see the moon pass slowly over and hide several of the sisters’ stars from view.
And although this will look fabulous with the naked eye, I strongly encourage you to use a pair of binoculars because not only will the moon with earthshine look great but you’ll also see dozens more stars in this cluster. It is actually a group of about 100 stars, 407 light years away, which means the light we’ll see next week left these stars 407 years ago in 1601, only nine years before Galileo was the first to use a telescope to discover the extra sisters.
I strongly suggest that you start watching at dusk just before it gets completely dark out and have a fairly clear flat horizon because the moon and the Pleiades will set about three hours after dusk. And as it gets darker, you can look to the left of the moon and the Pleiades and you’ll see the dim v-shaped group of stars called the Hyades which mark the face of Taurus, the bull.
In fact, Taurus’ red-eye star Aldebaran should easily catch your attention as will Betelgeuse, the red-shoulder star of Orion the Hunter and the red planet Mars, which on Friday, April 11, will be visited by a wonderful first quarter moon.
Every once in a while, a planet lines up with stars or other planets and creates an eye-catching cosmic triangle. Such is the case right now with Mars and the two brightest stars of Gemini, Castor and Pollux. Once you understand how different these three objects are from each other, you’ll want to rush outside and see them.
During the first two weeks in April at about 10 p.m., face west. Extremely close to the horizon getting ready to set, you’ll still be able to see the brightest constellation of winter Orion the Hunter. And to his left the brightest star we can see in the sky, Sirius the eye of his bigger dog. But directly above Orion you’ll see three objects, which if connected by lines, make an exquisite right triangle. The object closest to the horizon is Mars. Directly above are the two brightest stars of the constellation Gemini the twins, Castor and Pollux, with Pollux being slightly brighter.
Every April, I remind you of how you can have fun with the Big Dipper in the early evening because it is positioned in such a way that it gives credence to folk saying. Plus it is so high above the horizon, it can be used to easily find two wonderful stars of spring.
Any night in April between 8 and 10 p.m., look due north and you’ll see the Big Dipper almost directly above and just to the right of the North Star, its cup pointed down in such a way that if it were filled full of water, the water would be pouring out directly onto the ground below which gives a celestial significance to that old saying "April showers bring May flowers."
Because every April in early evening the biggest water dipper of the heavens is indeed positioned so that it is pouring its imaginary water onto the Earth below. Plus, because it’s so high above the horizon, it makes it very easy to use the three stars of the Dipper’s handle as a finder to locate two wonderful stars of spring which are also very high above the horizon.
Simply draw an imaginary line through the handle of the Big Dipper and extend it in the same curve or arc as the handle and you’ll "arc to Arcturus," the brightest star of Bootes the Herdsman.
Then if you extend that curve, that arc, on from Arcturus you can speed on to Spica, the brightest star of Virgo, the Virgin. Once again, using the handle and its curve, arc to Arcturus then speed on to Spica. What could be easier?
Now brighter Arcturus is relatively close – only 37 light years away. That means we see the light that left it 37 years ago (1971).
Spica, however, is seven times farther away – 260 light years – than Arcturus. That means we see the light that left it 260 years ago and 28 years before the signing of the Declaration of Independence.
But to make finding Arcturus and Spica even more special, just remind yourself that when we look at them now we are really looking back in time, because when I say that Arcturus is 37 light years away, I really mean that when you look at Arcturus this month you are not seeing Arcturus as it actually exists now in the present but as it existed 37 years ago. And when you speed on to Spica and look at it this month you are really seeing Spica as it was 260 years ago.
So find the Big Dipper this month as it rains down April showers for May flowers, then arc to Arcturus 37 light years away and speed on to Spica 260 light years beyond.
Keep looking up.
Jack Horkheimer is executive director of the Miami Museum of Science. This is the script for his weekly television show co-produced by the museum and WPBT Channel 2 in Miami. It is seen on public television stations around the world. For more information about stars, visit www.jackstargazer.com.