CLOSE ENCOUNTER WITH A COMET: Today, Dec. 16th, Comet 46P/Wirtanen is making an historic close approach to Earth–only 11.5 million km away. This puts Wirtanen in the top 10 list of comet flybys during the Space Age. It’s easy to find in the constellation Taurus, shown here in a photo taken just last night by Alan Dyer of Gleichen, Alberta:

This is Comet Wirtanen 46P in Taurus on December 14/15, 2018 accompanied by a Geminid meteor, caught by chance of course. The meteor has left a yellowish “smoke” cloud.
Yellowish Aldebaran and the Hyades are at bottom, the pink California Nebula (NGC 1499) is at top, in Perseus, while the blue Pleiades are at centre. They form a nice colour contrast with the cyan-green comet. The Taurus Dark Clouds of interstellar dust are at left.
Comet Wirtanen was two days before its closest approach to Earth and nearly at its brightest. It was visible to the unaided eye.
I got a chance to capture this and other views after Chinook clouds cleared off near midnight on Dec 14/15.
This is a stack of 5 x 2-minute exposures with the filter-modified Canon 5D MkII camera at ISO 800 with the Sigma 50mm lens at f/2.8. The meteor is from one of those frames. The camera was on the Star Adventurer tracker.[/caption]

“This is a tracked image with my camera mounted on a Star Adventurer tracker,” says Dyer. “A sporadic meteor dashed through the field of view during the 2-minute exposure–a busy sky!”

Dyer caught Comet 46P/Wirtanen splitting the gap between the Pleiades star cluster and Aldebaran, the red eye of the Bull. These are excellent landmarks that can guide you to the comet tonight. Indeed, you might need the help.

Although the comet is very close to Earth, it is not very bright. 46P/Wirtanen is a relatively small comet and, thus, barely visible to the unaided eye despite its proximity. Rural observers describe it as a faint misty cloud of 4th magnitude, about the size of a full Moon. It is nevertheless an easy target for digital cameras. Even a short exposure reveals the comet’s spherical form and emerald green hue.

Still can’t find it? Try using binoculars. Observers in urban areas say they are having good luck finding Wirtanen using hand-held optics. Simply scan the constellation Taurus for the green blob. Sky maps: Dec. 15, Dec. 16



From the Hubble, we have this image of the Ghost Nebula.
This deep space object is located in Cassiopeia.


Something for those chilly nights. Get a peek for one will not have another chance to enrich their experiences and tales for the grandkids.

A HYPERACTIVE COMET IS APPROACHING EARTH: Small but hyperactive Comet 46P/Wirtanen is approaching Earth and could soon become visible to the naked eye. On Dec. 16th, the kilometer-wide ball of dirty ice will be less than 11.5 million km away–making it one of the 10 closest-approaching comets of the Space Age. It already looks magnificent through amateur telescopes. On Nov. 26th, Gerald Rhemann took this picture using a 12-inch reflector in Farm Tivoli, Namibia:

“The comet is currently gliding through the southern constellation Fornax,” says Rhemann. “If you look carefully at the image, you can see galaxy NGC 922 near the comet’s head, and another galaxy ESO 479-2 on the left.”

Rhemann says that the comet’s emerald green atmosphere is 50 arcminutes wide. In other words–almost twice as wide as a full Moon. Its apparent diameter could double in the weeks ahead as the comet comes even closer. Because Wirtanen’s brightness is spread over such a wide area, it is diluted just below the limit of naked eye visibility, with a current magnitude near +6.0. We don’t yet know if the comet will ultimately become visible to the unaided eye–but it will certainly be an easy target for binoculars and backyard telescopes in December.

The nucleus of 46P/Wirtanen is small (~1 km) compared to greater comets such as Hale-Bopp (~30 km) and Halley (~15 km). It makes up for this deficit by hyperactivity. Recent measurements show that the core of 46P/Wirtanen is spinning once every 8.9 hours and spewing almost 1028 water molecules every second. This exceeds the expected production of such a small comet. [snip]


Here’s a preview of December Skies. At different times during the month, features of Sky and Space will be posted.


From Space

A COMET WITH TWO TAILS: Newly-discovered Comet Machholz-Fujikawa-Iwamoto (C/2018 V1) has sprouted a tail. Actually, two tails.  Michael Jaeger of Jauerling, Austria, photographed them both on Nov. 18th as the comet was gliding through the star fields of Virgo:
Why does Comet Machholz-Fujikawa-Iwamoto have two tails? Almost all comets do. The sun-warmed nucleus of a comet spews a mixture of dust and gas into space. Quickly, the mixture separates into two distinct tails: The gaseous “ion tail” is pushed straight away from the sun by solar wind. The weightier dust tail resists solar wind pressure and aligns itself more or less with the comet’s orbit. In Jaeger’s short video, the long ion tail points up and left; the stubby dust tail points up and right.

Comet Machholz-Fujikawa-Iwamoto appears to be a first-time visitor to the inner solar system. It is plunging toward the sun on nearly-parabolic orbit that will take it just inside the orbit of Mercury. Closest approach to the sun (0.38 AU) is on Dec. 3-4; closest approach to Earth (0.67 AU) is Nov. 27th. Amateur astronomers can find it–and its two tails–shining like a star of 8th magnitude in the constellation Virgo in the pre-dawn sky.


November 23 Full Moon. The Moon will be located on the opposite side of the Earth as the Sun and its face will be will be fully illuminated. This phase occurs at 05:40 UTC. This full moon was known by early Native American tribes as the Full Beaver Moon because this was the time of year to set the beaver traps before the swamps and rivers froze. It has also been known as the Frosty Moon and the Hunter’s Moon.


Here’s a preview of November Skies. At different times during the month, features of Sky and Space will be posted.