Wednesday, June 09, 2010

"Comet in the June Dawn"

photo by John Chumack

photo by Michael Jaeger

by Greg Bryant -

We rarely see a good comet when it's at its best. Most comets are brightest when nearest the Sun — just when they’re most likely to be hidden in the Sun’s glare or below the sunrise or sunset horizon.

That's the situation this spring with Comet C/2009 R1 (McNaught). Even so, observers in the Northern Hemisphere should be able to pick it up with binoculars just before dawn for at least part of June, during its runup in brightness.

And in fact, the comet is turning out to be 1 or 2 magnitudes brighter that we predicted in the June Sky & Telescope (page 60). Let's hope this behavior keeps up!

...Mid-June is when Comet McNaught should be most interesting, offering the best compromise between its increasing brightness and its decreasing altitude at the start of dawn. Moreover, the sky will be free of moonlight.

The helpful conjunctions continue as the comet passes about 1° north of the open cluster M34 in Perseus on the morning of June 10th, and 3° south of 1.8-magnitude Mirfak (Alpha Persei) on the 13th. It’s still about 15° high in the northeast as the sky starts to grow light on June 15th, but it appears roughly 1° lower every day after that. The comet passes zero-magnitude Capella on the 21st, and it’s very low by the 24th, when it passes 2nd-magnitude Beta Aurigae. By now Comet McNaught may be as bright as 4th or 5th magnitude, but moonlight is returning.

The comet will be lost to view by June’s end — just before it reaches perihelion on July 2nd, 0.405 astronomical unit from the Sun. It remains far from Earth throughout this apparition, never venturing closer than 1.135 a.u. (in mid-June). After perihelion it will fade rapidly as it heads to the far-southern sky.

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