Astronomy Picture of the Day (2007 Oct. 29) Explanation: What's happened to Comet Holmes? A normally docile comet discovered over 100 years ago, Comet 17P/Holmes suddenly became nearly one million times brighter last week, possibly over just a few hours. In astronomical terms, the comet brightened from magnitude 17, only visible through a good telescope, to magnitude 3, becoming visible with the unaided eye. Comet Holmes had already passed its closest to the Sun in 2007 May outside the orbit of Mars and was heading back out near Jupiter's orbit when the outburst occurred. The comet's sudden brightening is likely due to some sort of sunlight-reflecting outgassing event, possibly related to ice melting over a gas-filled cavern, or possibly even a partial breakup of the comet's nucleus. Pictured above through a small telescope last Thursday, Comet Holmes appeared as a fuzzy yellow spot, significantly larger in angular size than Earth-atmosphere blurred distant stars. Although Comet Holmes' orbit will place it in northern hemisphere skies for the next two years, whether it will best be viewed through a telescope or sunglasses remains unknown. Astronomy Picture of the Day (2007 Oct. 29) Erupting Comet Holmes

Astronomy Picture of the Day (2007 Oct. 26) Explanation: Comet 17P/Holmes stunned comet watchers across planet Earth earlier this week. On October 24, it increased in brightness over half a million times in a matter of hours. The outburst transformed it from an obscure and faint comet quietly orbiting the Sun with a period of about 7 years to a naked-eye comet rivaling the brighter stars in the constellation Perseus. Recorded on that date, this view from Tehran, Iran highlights the comet's (enhanced and circled) dramatic new visibility in urban skies. The inset (left) is a telescopic image from a backyard in Buffalo, New York showing the comet's greatly expanded coma, but apparent lack of a tail. Holmes' outburst could be due to a sudden exposure of fresh cometary ice or even the breakup of the comet nucleus. The comet may well remain bright in the coming days. Astronomy Picture of the Day (2007 Oct. 26) Erupting Comet Holmes

Campus Observatory At Resarch 1 building Monday 29 October: Start Time ~8:30 PM. Monday 12 November: Start Time ~8:30 PM. Monday 26 November: Start Time ~8:30 PM. Call observatory at 703-993-9558 Wait in the lobby

Advanced Question Chap. 8, Q31 in P206 Three-quarters of the radioactive potassium (40K) originally contained in a certain volcanic rock has decayed into argon (40Ar). How long ago did this rock form?

Advanced Question Chap. 8, Q31 in P206 Answer: \What is left of Potassium is 1-3/4 = ¼ ¼ = ½ X ½ Which means two half-lifes have passed for the Potassium From page 190, the half-life time of Potassium is 1.3 billion years. Therefore, the volcanic rock is 2 X 1.3 = 2.6 billion years old