Stellar scintillation

Did you ever sing the little ditty that goes, "Twinkle, twinkle, little star. How I wonder what you are. Up above the world so high. Like a diamond in the sky?

Did you ever wonder why stars twinkle? What makes the starry host as viewed from a dark-sky place seem to look like so many blinking Christmas lights against a dark background?

Why do stars twinkle? The answer is quite simple, it is caused by stellar scintillation. See, isn't that easy?

Stellar scintillation is a big, fancy term for when turbulence in Earth's atmosphere bends (refracts) star light many times and in random directions. This bending causes the light to look like it is moving a bit and winking in and out.

When this action enters our eye and goes to our brain, the brain interprets it as twinkling. When viewed from outer space, stars do not twinkle.

Conversely, neither do planets. Planets are much larger than pinpricks of light so atmospheric turbulence does not affect them so they don't appear to twinkle--unless the atmosphere is very turbulent. Or as an astronomer would say, "lousy seeing."

Okay, why all this stuff about twinkling stars. Because tonight, and for the rest of January and February and perhaps even into March one of the sky's premier twinklers will be on display in the evening sky about one to two hours after local sunset. Look just above the southeast horizon for our old friend, Orion, the Hunter.

Find the three stars of Orion's Belt and extend a line through them down toward the horizon until you find a very bright star--Sirius, the Dog Star. Sirius is the brightest star in Canis Major, the Big Dog. It is also the brightest star in the night sky.

Sirius will be close to the horizon and its light will be traveling through the thicker part of Earth's atmosphere, thus it should be a real sparkler. If you really want to see it sparkle, view it through a pair of binoculars and prepare to have your socks knocked off.

If it is cloudy, or the horizon is clouded out not to worry, it will be in that position into early March, just remember to keep your viewing time close to sunset.

Now, how about a few more things to see with that new telescope.

You may want to wait until March or April, but the giant planet Jupiter is above the eastern horizon at about midnight. You could view it earlier, but that same atmospheric turbulence we just discussed will apply to Jupiter.

I might not twinkle, but it won't stand still either. If you wait until it is higher above the horizon the seeing will be much better, otherwise it will look like a pot of boiling oat meal.

Since we are out early, and we just used Orion to find Sirius, go back to Orion and point your scope to the middle "star" of the sword. You will see it is not a star at all, it is a giant nebula, and a jewel for observing it is.

Just remember, It won't look like all the photographs in the fancy magazines, it will appear a slight shade of gray. Since we were looking at Sirius earlier, how about looking at an open star cluster?

About five degrees below and right of Sirius is the open cluster M-41, also called the Little Beehive. Check it out with binoculars first.

SKY WATCH: First quarter moon, Saturday, January 16. January 15, moon below and right of Uranus, the next day above and left of the planet.

NEXT WEEK: More objects to look for and more astronomical blathering.