Lepus, the noble bunny


Tom Burns - Stargazing



At Perkins, we spend quite a bit of time in the winter talking about Orion and his environs. His faithful huntin’ dawg Canis Major follows at his feet. His club is raised in unending battle with the pugnacious bull, Taurus. He stands with brave resolution on a helpless bunny.

In the latter case, we’re talking Lepus, the Hare, a somewhat sturdier version of our domestic rabbit. In fact, Orion has good reasons for standing on the bunny.

In fact, the reason for Orion’s odd fortitude traces far back to a massive and deadly (no kidding) outbreak of rabbits on the Greek island of Leros. Orion was strong. Orion was brave. Orion killed all the bunnies.

You know, come to think of it, the story is a pretty good one. Perhaps I’ll tell it to you sometime.

We spend little time talking about Lepus up at Perkins. Its stars are faint compared to the intensity of Orion’s bright stars, and the constellation is practically erased by the light pollution from Columbus, our neighbor city to the south. It isn’t exactly full of objects for the stargazer to look at.

One object is a globular cluster marked as M79 on most star maps. This dense ball of more than 100,000 stars is as bright as perhaps 90,000 of our suns, but it’s so far away that it isn’t much to look at.

M79 is visible in binoculars as a faint, fuzzy patch. A moderate-sized telescope will begin to resolve some of the stars around its edges. At 42,000 light years away from Earth, M79 is about as far away as you can get and still be in our Milky Way galaxy. (One light year is equal to six trillion of your puny Earthling miles.)

It took 170 years after the invention of the astronomical telescope for French astronomer Pierre Méchain to stumble upon it in 1780. Still, it’s worth a look if you can escape the city light pollution and if you have access to a telescope big enough to resolve it into a myriad explosion of stars.

The diehard telescopists among us have noted its odd shape and informally dubbed it the “Starfish Cluster.” Check it out if you get a chance.

Lepus wouldn’t be worth bothering about except for one really strange and spectacular star called R Leporis. Long ago, when I was the one on the front lawn at Perkins pointing a telescope, I always found time to point my big ‘scope at this strange star.

Over about 428 days, “R” changes from very dim, so that it can be seen only in a large telescope, to bright enough so that it can be glimpsed by the naked eye under very dark, rural skies, and back to bright again.

Such variable stars have extreme changes in their brightness because they’re very old.

As stars get older, they have less and less hydrogen to burn into helium. As their thermonuclear fires falter, they cool off. The explosive pressures at their center cause them to expand to enormous size, radiate a lot of energy into space, and get temporarily brighter.

As heat and light is radiated, the central explosive pressures lessen. Gravity takes over, allowing them to contract a bit and become dimmer. This cycle can repeat itself millions of times before the star finally burns out.

At less than 6,000 degrees Fahrenheit, R’s temperature is much lower than that of a yellow star like our sun, which is medium hot at 10,000 degrees.

Its low temperature allows R to keep a lot of carbon in its shell. As its light shines through its atmosphere, the blue light is filtered out by the carbon, which enhances its distinctly red color- already quite ruddy owing to its relative coolness.

And that’s what makes R so special. In a sky filled with white stars, bluish stars, and even pale orange stars, R shines a deep crimson.

Its discoverer, J.R. Hind, described it in 1845 as “resembling a drop of blood on the background of the sky.” Color, especially red, is hard to discern at night. Hind’s Crimson Star, as R Leporis is sometimes called, simply blows you back from the telescope.

Observing a star like R can be a frustrating experience because its brightness affects its color. One year, it is easy to find in binoculars, but it looks more coppery than red. The next year, only a telescope will show it, but then it looks like a glowing drop of deep red wine on the face of the night.

However, its bright red color never fails to amaze. Observed over time, it looks like a crimson heart beating oh-so-slowly to the rhythm of the cosmos.

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Tom Burns

Stargazing

Tom Burns is director of the Perkins Observatory in Delaware.

Tom Burns is director of the Perkins Observatory in Delaware.