Sky Talk January 2010: A Celestial Kaleidoscope

The sky abounds with analogies to things terrestrial. (After all, the starry heavens were the story and history books of the ancients.) In next month’s installment of this column, we’ll be exploring a celestial campfire. Here we discuss a most colorful and fascinating device with which we’re all familiar — the kaleidoscope. But this one is in the sky!

“Incidentally, it may be mentioned that for the casual visitor who merely wishes to see something brilliant and surprising, few objects excite more admiration than a first-magnitude star thrown slightly out of focus.” So wrote the famous astronomer William H. Pickering back in 1917 to describe his experience with showing the stars to thousands of visitors at his observatory through a telescope. This is also true if using a pair of binoculars — and even the defocused unaided eye.

Pickering’s remark is especially apt (and sensationally so!) if the star happens to be the brightest in the entire sky seen at a time when it’s just rising above the eastern horizon in early evening. That star is radiant Sirius, leader of the entire heavenly host. And the time is now — in mid-winter with its crystal-clear sparkling nights. This wondrous luminary is normally blue-white in color. But at this time of the year atmospheric turbulence is at its greatest, as the Earth quickly radiates its accumulated daytime heat into the cold night sky. The churning turbulent layers of air lying near the horizon act like multiple prisms, with the result that normally-blue Sirius flashes glorious prismatic rays of every imaginable heavenly hue from its pulsating heart! Here truly is a kaleidoscope of cosmic proportions!

To be sure you’re looking at just the right time for maximum effect, first get as unobstructed a view of the eastern horizon as possible (the seashore being ultimate for the purpose!). Next, set your Edmund Scientifics Star and Planet Locator (#30092-27) to see what time Sirius rises on whatever date this month you’re out observing. For example, on January 15th this great star just pops over the horizon at 6 p.m. as seen from mid-northern latitudes. (The corresponding time is 7 p.m. on the 1st and 5 p.m. on the 31st.) For most observers, the best view will actually come 5 to 10 minutes or more after the star rises, allowing time for it to get up and out of the densest atmospheric layers at the horizon that dim its light. The effect can still be seen for an hour or longer, but continues to decrease the higher Sirius gets in the sky.

If you’re fortunate enough to have a small telescope like the Scientifics Astroscan at 16x or the more recently introduced Celestron FirstScope (#31512-75) at 15x, simply defocus the eyepiece (in or out — try both ways) slightly while pointed at Sirius. If you don’t (yet!) own a telescope, look at the star with your Edmund binoculars slightly defocused. And if you have no optical aid available at all but are near-sighted, simply remove your glasses to get much the same effect.

–James Mullaney
Former assistant editor at Sky & Telescope magazine and author of seven books on stargazing.

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