Naked Eye Comet

By Michael on October 24, 2007 at 2:59 pm | In Blog Posts |

The folks over at space.com are reporting on a comet that has brightened ridiculously and is now visible to the unaided eye.

Comet Holmes…was no brighter than magnitude 17 in mid-October…But the comet’s brightness has suddenly rocketed all the way up to 3rd-magnitude, brightening nearly 400,000-times in less than 24-hours!

Go try see it.

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  1. This almost certainly indicates that the nucleus has split into several pieces. If so, there may be even more activity in the next while.

    Comment by dougwelch — October 24, 2007 #

  2. I took a look tonight. It looked non-stellar to me and about V=3 or so. It looked redder than Delta Persei (which is quite a blue star at B-V=-0.12).

    Comment by michael — October 24, 2007 #

  3. This almost certainly indicates that the nucleus has split into several pieces.

    This may be naive, but if L2/L1=400,000 and the luminosity is proportional to R^2 then the new radius R2=R1*sqrt(400000)=R1*600. So the nucleus got 600 times bigger?

    Comment by michael — October 24, 2007 #

  4. The brightness of a comet usually depends on the activity from certain spots on its surface. These spots generally are a small fraction of the surface area. When a comet breaks up, it exposes a huge amount of active surface at once.

    The active areas spew gas and dust into space resulting in a luminous volume far more effective at scattering light than the tiny (and usually very dark) nuclear surface of the comet.

    Comment by dougwelch — October 25, 2007 #

  5. This is also an unusual event in that the comet never gets all that close to the Sun. Its maximum distance from the Sun is 5.2 AU (Jupiter-ish) and its minimum distance is 2.2 AU (outside the orbit of Mars). Since it has apparently done this before, it may be an out-gassing event instead of a break-up - we’ll know more soon!

    Comment by dougwelch — October 25, 2007 #

  6. The active areas spew gas and dust into space resulting in a luminous volume far more effective at scattering light than the tiny (and usually very dark) nuclear surface of the comet

    Still, if we assume that this wasn’t happening before and it is happening now and that the light is all reflected (i.e. no change in temperature) then we are seeing an increase in effective surface area, aren’t we? And perhaps a change in albedo.

    Comment by michael — October 26, 2007 #

  7. From what I’ve read, this comet had outbursts before, but nothing as great as the current apparition.

    We showed it off to the public last night at our observatory’s open house, and by the time we left you could easily see that it was non-stellar even to the naked-eye.

    Comment by Kevin — October 28, 2007 #

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