Tuesday, October 29, 2013

A Halloween Star and an Exploding Comet

Click on image for larger view

This is comet 17P/Holmes near the "Demon Star", Algol. I took this picture almost 6 years ago, a year before I started this Photo Blog, so many have not seen this image. I put this up for two reasons.

  • First, there is a fairly new comet that is very similar to comet Holmes. Both of them are "exploding" comets. Back in October 24, 2007, comet Holmes shocked astronomers with a spectacular eruption. In less than 24 hours, this extremely faint comet (17th magnitude), brightened by a factor of nearly a million and became a naked eye object. At the time I took this photo in January, it had expanded into an object larger than the Sun. The new comet, C/2012 X1 Linear, is now doing the same thing. It was seen to first explode on October 20th of this year and amateur astronomers have seen the comet's brightness increase 100 times. It is not as bright as Holmes at this point, but can be captured by astrophotograhers. See the middle of the page on Spaceweather.com for pictures and where it is located in the morning sky.
  • Second, in the above photo, comet Holmes passed near the bright, naked eye star Algol, in the constellation Perseus. Algol is usually the second-brightest star in Perseus, but only when it is not being eclipsed by it's companion star. During the eclipse, which occurs regularly every 2 days, 20 hours and 49 minutes, Algol dims from 2.1 magnitude to 3.4 and lasts roughly 10 hours. This "dimming" can be seen without the aide of a telescope, so more than likely it was known in ancient times, but the variability of Algol was first recorded in 1667.
What makes this a good "Halloween" star is the mythology involved with this star: Perseus, the mythical Greek hero, used the Gorgon Medusa's severed head to turn the sea monster Cetus into stone. Algol represented the "evil eye" of Medusa to the ancient Greeks. An evil eye that winks at you for 10 hours approximately every 3 days.

We know Algol as the "Demon Star", derived from Arabic "ra's al-ghul", meaning "head of the ghoul". In Hebrew folklore, Algol was known as "Rosh ha Satan", or "Satan's Head". In Chinese astronomy, it is known as the Fifth Star of the Mausoleum and also had the grim name "Tseih She", meaning "Piled up corpses". What better star than this for "All Hallows Eve"?

Click on image for a larger view
During the Fall and early Winter, Algol can be located high in the north east sky after sunset.

Chart created with SkySafari Pro.
Comet Holmes image was taken with a 300mm f/4 Canon lens on a Canon Xti DSLR piggybacked on telescope. 29 - 2 minute exposures.

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