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Skywatch: How to find the dimmest constellation visible from Idaho
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Skywatch: How to find the dimmest constellation visible from Idaho

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Some constellations are conspicuous, comprising one or more bright stars, a distinctive pattern of stars, or both. Others are so faint that they require diligence to spot.

The ancient Greeks defined most of the star patterns recognized today, but made no effort to include the fainter stars, calling them “amorphotoi” (unformed).

By the 18th century astronomers had decided to repurpose the constellations as a way to subdivide the celestial sphere. Doing so required defining new constellations from the inconspicuous stars, so that every location in the sky was spoken for.

The last “empty” spots were filled in by French abbot and astronomer Nicolas-Louis de Lacaille, who traveled to the Cape of Good Hope, South Africa in 1750 to establish a surveying baseline from Paris for triangulating the distance to the sun and moon. Because the southernmost sky was never visible to the ancient Greeks, he defined fourteen new constellations, published posthumously in 1763.

Among Lacaille’s constellation inventions was Mensa, the Table Mountain, representing the iconic landmark overlooking Cape Town. The remaining thirteen included commemorations of the technology of the age, including the alchemist’s furnace, the compass, the telescope, the pendulum clock, and the microscope.

While Mensa, whose lucida (brightest star) is the dimmest of the 88 constellations, never comes above the horizon in Idaho, Microscopium, with the second dimmest lucida, does.

This time of year it appears hugging the south-southeast horizon at the start of morning twilight. Its brightest star, Gamma Microscopii, is dimmer than the faintest star of the Little Dipper. To find it, you’ll need to be at a dark location, away from city lights. Look about twenty degrees (an outstretched hand span at arm’s length) to the right of Fomalhaut, the brightest star near the southeast horizon around 3:30 a.m.

Next column: The length of the seasons.

Chris Anderson manages the College of Southern Idaho’s Centennial Observatory in Twin Falls. He can be reached at 732-6663 or


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