Comet Holmes shines above the street lamps

Session name: 20071106.2000

Skies cleared up after the rain where a naked eye limiting magnitude was in the neighborhood of magnitude 5. Comet Holmes continues to be seen naked eye from New York City, even from well lit spots in the city. Find some shade if you can and look toward Mirfak to see an obvious non-stellar object nearby.

Artists' Rock, an outcrop of Manhattan Schist behind Artists' Gate is not the ideal place to observe from (view of area) yet this photo shows a good likeness of the night sky with acute vision unaided. The four brighter stars of Alpha Persei Association show between Mirfak and delta Per.

The comet continues grow in size, my estimate based on ~7 comet diameters to in the 22x60 binoculars' 2.1° field of view is about 18'. The brightness profile consists of an evenly illuminated central condensation surrounded by a paler ring. The coma is about 3 central condensation diameters across. The psuedonucleus was not detected. In acsii it could appear like __/---\__

Its location has moved west, north of west, morphing the right triangle it created with Mirfak and delta Per last week to a flat isosceles.

I find the observation with 7x50 binoculars to be the most pleasing. It takes in the large, richer field of stars that contrast sharply with this dandelion interloper, ready for a breath of air to blow it apart.

Another pleasing view was the Double Cluster observed in the Tak bins. Framed nicely the clusters reveal the stardust that clings around some of the brighter stars; all the while sitting on a bed of uneven faint light.


Marked up photo || unmarked photo

20071030 - 17P/ Holmes Observing Report

Sketch in Moleskine notebook & astromick image on iPhone.

Prior to a brief session, I attended the monthly planetarium show, Celestial Highlights, at New York's Hayden Planetarium. Comet Holmes was given some time both as an object in Perseus and in a series of slides given at the end of the sky tour.

The presenter described Comet Holmes as difficult from the city with unaided eye but revealing in binoculars and scopes. I wanted to disagree but it was his show. He followed up with three images of the comet (one by Pete Lawrence) and for contrast, showed Comet Hale-Bopp with two tails trailing long and high into the sky.

After the show, I went for a brief session to TotL to take in the comet naked eye and with the 22x60 binoculars. I carried the Tele Vue Ranger to get tighter shots of the comet but it wasn't unpacked.

On my way around the Great Lawn I ran into Mark the Literary Agent. He stayed and we observed the comet and the passing people watching the two guys watching a comet. I didn't invite people to the bins nor did anyone ask but a few. One was Ken the Pilot who stopped to say, "Hello." He peeked in the bins and said, "Oh that's the comet. Not that impressive." I described the same features to look or that I described to Mark earlier.

My observation is that comet 17P/Holmes appears to be dimming. I compare to delta Per which is celestial-South, or around 9:00PM EDT, directly to the right naked eye. Their brightness looks nearly equal. The pedestrians that stopped to observe it naked eye agreed. They added the description that it looked fuzzy compared to the other stars (naked eye). Same observation to me. Late last week, the comet's brightness was almost midway between the brightness of delta Per and Mirfak, alpha Per. The comet's size is obviously growing.

Location in field of view
There are two ways that I help the pedestrians look for the comet, one from the direction of Cassiopeia and the other from Capella in Auriga. Around 9:00PM EDT, Capella has risen almost 25­° above the horizon due manhattan-north. The brightest star in the area is unmistakable and difficult to miss. With an extended, open right hand put your thumb on Capella and rotate your pinky up to about a one o'oclock direction. You'll notice another bright star, Mirfak. Consider Mirfak the apex of a tall, isosceles triangle. Two fainter stars are seen below Mirfak. Relax, give it a moment or two for your eyes to adjust to see the triangle. The base star to your left, may appear fuzzy, since this is the comet. Easily seen from the city as many pedestrians made it out with a little coaching.

In the binocular 2 degree field of view, the comet appears near the inside right corner of a right triangle. These three stars: mag 6.18-HIP17772; mag 7.72-HIP17713; and, mag7.55-HIP17476. In my mental image 17772 & 17713 are the base of the right triangle.

Size
The separation between the two base stars is 23'15". I estimate that separation to be 2 1/4 ~ 2 1/2 comets yielding a size of 9.3' ~ 10.3' for the head of comet.

Brightness
I didn't perform an in-out test for brightness. That is choosing stars of similar magnitude and bring them out of focus so that the star's size increases to s large as the diameter of the comet. If the comet's brightness appears equal to the star's de-focused brightness then the comet's brightness is assigned a value of the star used for testing.

The outer coma exhibits an uneven brightness, a darkening can be seen on the leading edge side. It is arcuate and extends almost halfway around the central condensation (what I have been calling the nucleus.)

As the comet grows larger its surface brightness decreases. The brightness is distributed across a greater surface area of the comet. (Consider the brightness and the appearance of M33.) This results in less contrast with the background sky and appears dimmer to the eye.
With unaided eye, compared to delta Per, 17P/Holmes' brightness is approaching delta's brightness, Late last week it was almost midway between alpha Per (Mirfak) and delta Per. Over the past few days I feel it is dimming, due to the explanation above.

Shape
The comet appears round with three sections of varying brightness. The coma appears with a bright central core which is about two-fifths of the comet's diameter and off-center relative to the outer coma ring. It is south of the leading (drift) direction. Within that brighter central condensation on its trailing side, a stellar condensation is evident. Its obvious in most photographs of the comet. I did not see any evidence of a tail.

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With the gang - 17P/Holmes

Session name: 20071027.1935

Larger images: Marked up | Unmarked
Compare with this Perseus image from this post, where Comet Holmes is obviously unseen in the general area.

The comet continued to capture out attention and interest. Under other circumstances a disappointing lunar occultation of the Pleiades past midway on our moonrise would have been center stage. But not. Not with the comet of 2007 juicing up Perseus. Tycho had SN1572 in Cassiopeia and we have comet Holmes. Different as they are in nature is as great as the excitement of this new temporal light in the sky.

I arrived at TotL to see Ben already set up with his Tele Vue 76 aimed at Comet Holmes. He invited me to the scope asking if I saw any peculiar features. After getting eyepiece-adapted, a bright stellar point was visible on the interior, southwest edge of the nucleus. This larger nucleus continued to appear off center towards the east-southeast direction (towards the trailing side in the refractor's field of view) within the coma. The coma's circumference had a bright, consistent brightness, however, its interior was uneven with some dark patches. This was most pronounced on the leading edge, like a backward "C". This was the greater side of the coma as mentioned earlier that the nucleus was slightly displaced to the trailing side. AAA'er Bruce Kamiat (report) pointed out this feature which Ben & I agreed to seeing.

Ben & I disagreed on sizes. At first, I grossly over-estimated the size with a wrong mental image of Jupiter. I suggested the size of the nucleus to be something four jovian diameters, the overall sie of the head to about 6 jovian disks. Ben's estimate was more reserved as one jovian disk. Mars had cleared the trees so we used the ~12 arc second martian diameter to measure the components of the comet's head. I estimated the nucleus to be 3~4 martian diameters across, if I remember Ben's was less. On the leading edge, the coma was about 2 nucleus diameters and on the trailing edge about 1 1/2 nucleus diameters.

Down to our south, an area we call Turtle Pond Observatory (TPO) another crowd of astronomers had naked eye and optics turned to the sky to show the passing public. Turns out it was Kentaurian with some of the AAA'ers: Rich Rosenberg, Bruce Kamiat, and Joe; Rik Davis joined shortly after. They came up to TotL to join in on the cheer. Hawaiian George came by and so did Team Totl'er Kin riding in with a small group of TIME'S UP! riders led by Rich. Debbie, a dog owner, who used to observe with us appeared tonight. We had a thin regular flow of pedestrians passing through as we were eager to share sights with pointed fingers and optics.

Seeing was not the best and a light breeze caused scope shake when the magnification was increased to 117x on the Takahashi refractor. When the air calmed for a steady view the Moon was absolutely stunning along the terminator. Cruising along the line sunset it was difficult to ignore craters Langranus and Petavius. Rimae Petavius runs across the crater's floor. To the northeast, sunset begins where the far eastern walls of Mare Crisium try to repel blackness. Not for long.

A small diversion while near the comet was to spot NGC1528. A bright open cluster that I prefer with a darker sky without a nearby ~17d moon. Tonight only the brighter members stood out in a loose, sparse arrangement of crisscrossing arcs of stars. The same comments apply for M31 and M32 but for one pedestrian we gave here a small survey of the different heavenly objects.

During our observing session we placed a towel on one of the street lamps to block of the glare in our direction. The other lamp to our east spilled its light casting long thin shadows to the west. From high in the east, Moonlight competed casting darker, harder, shorter shadows. Crisp as bacon.

Lastly we visited Mars before packing up. It was still rising and seeing was not greatat even at an altitude of ~34°. I thought I may have seen some detail at magnification 117x but it didn't agree with Brian Tung's Mars Map. I thought I saw a dark band running central across the diameter of the disk, rather a large chord instead of an equatorial band. The trailing limb had a greater darkening on it.

Kin, Ben and I packed up for the evening a bit past 1AM. We pulled the towel from the street lamp to bring back the illumination and shadows leaning east.