The Sun is no longer the largest object in our solar system. The recently visible-to-the-naked-eye Holmes comet has achieved that distinction today. The comet has a larger gas and dust cloud known as the coma, and consequently it has a larger diameter than the sun according to astronomers at the University of Hawaii. Scientists don't seem to have a guess as to how big it will ultimately become.
The Holmes coma's diameter on Nov. 9 was 869,900 miles (1.4 million kilometers), based on measurements by Rachel Stevenson, Jan Kleyna and Pedro Lacerda of the University of Hawaii Institute for Astronomy. The sun's diameter, stated differently by various sources, is about 864,900 miles (1.392 million kilometers).Holmes is still visible to the naked eye as a fuzzy star anytime after dark, high in the northeast sky. You can find it by using this sky map.
On Monday, Nov. 19, the comet will create a unique sky watching event according to the Web site Spaceweather.com: "The comet will glide by the star Mirfak [also called Alpha Persei] and appear to swallow it-a sight not to be missed.
"NASA's Hubble Space Telescope has watched the bright core of Comet 17P/Holmes, which mysteriously brightened by nearly a millionfold in a 24-hour period beginning Oct. 23, 2007. "This amazing eruption of the comet is produced by dust ejected from a tiny solid nucleus made of ice and rock, only 3.6 kilometers (roughly 2.2 miles) in diameter," The Hawaiian astronomy team wrote in a press statement. The new image from the Hawaiian observatory also shows a modest tail forming to one side, now just a fuzzy region to the lower-right. That's caused by the pressure of sunlight pushing on the gas and dust of the coma. But the comet is so far away-149 million miles (240 million kilometers), or about 1.6 times the distance from Earth to the sun-that even Hubble can't resolve its nucleus.
Comets have gotten a lot of attention this year. For example, in October NASA said one of its satellites captured the image of a solar hurricane ripping off the tail of a passing comet. The resulting collision saw the complete detachment of the plasma tail of Encke's comet, which was traveling within the orbit of Mercury, NASA said. The comet is only the second repeating, or periodic, comet ever identified and has the shortest orbital period - about 3.3 years - of any known comet. Halley's comet was the first.
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