[meteorite-list] Jan. 16 May Be Last Best Chance to Search for Comet ISON's Remains
From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Tue, 31 Dec 2013 12:38:04 -0800 (PST)
Jan. 16 May Be Last Best Chance to Search for Comet ISON's Remains
by Bob King
December 30, 2013
Comet ISON revolves around the sun in steeply inclined orbit. Earth will
pass through the plane of that orbit on Jan. 16. As we look "up" toward
the comet, ISON's dust stacks up along our line of sight and could appear
temporarily brighter. Credit: solarsystemscope.com with annotations and
additions by Bob King
Is there any hope of detecting what's left of Comet ISON after the sun
proved too much for its delicate constitution? German amateur astronomer
Uwe Pilz suggest there remains a possibility that a photographic search
might turn up a vestige of the comet when Earth crosses its orbital plane
on January 16, 2014.
On and around that date, we'll be staring straight across the sheet of
debris left in the comet's path. Whatever bits of dust and grit it left
behind will be "visually compressed" and perhaps detectable in time exposure
photos using wide-field telescopes. To understand why ISON would appear
brighter, consider the bright band of the Milky Way. It stands apart from
the helter-skelter scatter of stars for the same reason; when we look
in its direction, we peer into the galaxy's flattened disk where the stars
are most concentrated. They stack up to create a brighter band slicing
across the sky. Similarly, dust shed by Comet ISON will be "stacked up"
from Earth's perspective on the 16th.
This isn't the first time a comet has leapt in brightness at an orbital
plane crossing. You might recall that Comet C/2011 L4 PanSTARRS temporarily
brightened and assumed a striking linear shape when Earth passed through
its orbital plane on May 27.
Pilz, a longtime contributor to the online Comets Mailing List for dedicated
comet observers, has made a series of simulations of Comet ISON for mid-January
using his own comet tail program. He bases his calculations on presumed
larger particle sizes 1 mm-10 mm - not the more common 0.3-10 micrometer
fragments normally shed by comets. The assumption here is that ISON has
remained virtually invisible since perihelion because it broke up into
a smaller number of larger-than-usual pieces that don't reflect light
nearly as efficiently as larger amounts of smaller dust particles.
The images look bizarre at first glance but totally make sense given the
unique perspective. Notice that the debris stream becomes thinner as we
approach orbital crossing; any potential dust blobs appear exactly edge-on
similar to the way Saturn's rings narrow to a "line" when Earth passes
through the ring plane.
Besides the fact that not a single Earth-bound telescope has succeeded
to date in photographing any of ISON's debris, amateurs who attempt to
fire one last volley the comet's way will face one additional barrier
- the moon. A full moon the same day as orbital crossing will make a difficult
task that much more challenging. Digital photography can get around moonlight
in many circumstances, but when it comes to the faintest of the faint,
the last thing you want in your sky is the high-riding January moon. One
night past full, a narrow window of darkness opens up and widens with
each passing night.
Will anyone take up the challenge?
UPDATE Dec. 30 10 a.m. (CST): We may have our very first photo of Comet
ISON from the ground! Astrophotographer Hisayoshi Kato made a deep image
of the comet's location in Draco on December 29 using a 180mm f/2.8 telephoto
lens near the Mauna Loa Observatory in Hawaii at 11,000 feet. He stacked
5 exposures totaling 110 minutes to record what could be the ISON's debris
cloud. It's incredibly diffuse and faint and about the same brightness
as the Integrated Flux Nebula, dust clouds threading the galaxy that glow
not by the light of a nearby star(s) but instead from the integrated flux
of all the stars in the Milky Way. We're talking as dim as it gets. What
the photo recorded is only a tentative identification - followup observations
are planned to confirm whether the object is real or an artifact from
image processing. Stay tuned.
The sausage-like glow running from upper left to lower right in this negative
image may the dusty remains of Comet ISON as photographed on Dec. 29 from
Hawaii. The blue dot shows the predicted position of the comet; the green
type gives the names of stars. Click to enlarge. Credit: Hisayoshi Kato
Received on Tue 31 Dec 2013 03:38:04 PM PST