Comets & Asteroids

Tonight, Oct 7th, Comet 103P Hartley 2 will pass directly north of the double cluster, NGC869 and NGC884. The comet should be nearly at peak magnitude for this apparition, as it is near both close approach to the Earth (Oct 20) and perihelion (Oct 28th).

Through the night the comet will pass about 30' north of the center of both clusters, quite likely with coma and outlying cluster members intermingling. The view should be spectacular in binoculars or a low power telescope view. This will also be a wonderful photographic opportunity, as the clusters and comet will be well matched for magnitude. There will be no moonlight to interfere with the view as New Moon occurs today as well.

A comet visible to the unaided eye is an anticipated event amongst the amateur astronomy community. Sometimes we know the comet is coming, sometimes we get caught by surprise when a new comet is discovered, occasionally a known comet experiences an outburst and brightens dramatically. Whenever a bright comet offers, telescopes across the globe slew around to enjoy the spectacle, comets are to be enjoyed whenever they appear.

In this case the comet is a well known comet that is making a favorable apparition. Comet 103P/Hartley 2 will pass 0.12AU from Earth, a mere 11 million miles in October of this year. The near approach allowing even a modest comet to become quite bright. Predictions are that the comet will be brighter than 5th magnitude, easily visible to the unaided eye from a dark site.

The comet was discovered in 1986 by Malcolm Hartley. When discovered it became apparent that this was a periodic comet, one who's orbit was regularly within the inner solar system during a 6.4 year orbit, why hadn't it been discovered before 1986?.

Calculations showed that the comet had previously followed an orbit that never brought the comet closer than 1.6AU to the Sun, far enough away from the Sun to lessen the activity of the coma and escape detection. In 1982 the comet swung near Jupiter, where the strong effects of the giant planet's gravity modified the comet's orbit, changing its perihelion to a distance of 0.9 to 1.0AU. The comet now swings much nearer the Sun, the increased solar radiation nearer the sun creating a brighter coma and tail, leading to it's discovery and the occasional much better view for earthbound observers. This fall the comet will make a close approach to Earth, the best appearance since discovery, passing within 0.12 AU (11 million miles) on October 20th, 2010.

Currently the comet is visible in the constellation Andromeda, within easy reach of small telescopes. It is moving westward in the sky and will cross into Cassiopeia and Perseus over the coming month making it well placed for viewers in the northern hemisphere through the close approach. Its path takes it along the Milky Way and near any number of nebulae and star clusters. Around the 9th of October the comet will pass quite close to the Double Cluster, NGC 869 and NGC884, possibly providing a very nice photo opportunity.

While 5th magnitude is not that bright, it should be relatively easy to see under a dark sky. Even in mid-August the comet showed a small tail in photos, hopefully this tail will brighten to allow nice telescopic or even binocular views. In any case it should provide a nice photographic target. Of course when predicting the behavior of comets it is important to remember the words of comet discoverer David Levy... "Comets are like cats, they have tails and do exactly what they want"

Tonight at the VIS I had hoped to get a glimpse at Comet McNaught. This was not to be. Despite hoofing my 76mm refractor and an alt-az mount up a small cinder cone at 9000ft, the comet was not visible. I found Castor and Pullox easily in the twilight. Unfortunately the correct position for the comet put it just behind the ridgeline from my vantage point. I was stymied by the bulk of Mauna Kea itself.

It was a great night at the VIS, a good crowd, lots of questions all night long. Mild temperatures and no wind combined with a wonderful sky made for a perfect star gazing evening.

Tomorrow I am upping the ante in my comet hunt! I am scheduled to work the day at the summit anyway, so I will just stay up a couple more hours to sunset and attempt to find the comet from the summit, without the mountain in the way. If it is possible, I will see it from 13,600ft!

I am hoping to spot Comet McNaught while it is at it's brightest. But so far this exercise has proven futile, clouds getting in the way. This evening it wasn't clouds, but vog that made it impossible. As I was coming home I noted that I couldn't see Haleakala in the vog and haze, showing that a comet near the horizon was just not going to be spottable. I need to get above the vog!

Comet C/2009 R1, McNaught, is predicted to peak in brightness around July 1st at a little dimmer than second magnitude. This is easily visible to the unaided eye if the viewing conditions are favorable. Unfortunately conditions are not favorable, as the comet is quite near, or below the horizon after it gets dark. For the next few days the comet is approaching the head of Gemini, passing quite close to Castor and Pullox. This puts it quite low on the northwestern horizon at sunset, about 10° elevation, right above the Sun. Perihelion, or closest approach to the Sun will be July 2nd for the comet.

For much of the world the comet has ceased to be visible, the late twilight further north hiding the comet from view, southern observers are frustrated by the northern declination of the comet. But here in Hawai'i, or anywhere else of similar latitude, it should be possible, barely, to see the comet as it peaks in brightness. At least that is the answer I get from my computer as I examine dates and positions. I have to try it and find out.

For the next couple days the comet sets within a couple minutes of 8pm, while sunset is at 7:15, giving a nice window when spotting the comet should be possible. It will require a low and clear northwestern horizon. Fortunately I will have access to such a horizon tomorrow night, at the VIS. I will have to hike up Pu'u Kalepeamoa, but that is just a 5min walk from the VIS. From there the view is spectacular, even better if that view includes a bright comet sporting a tail!

The dwarf planet Ceres is the largest of the asteroids in the inner solar system at 932km (579miles) in diameter. This is enough mass and gravity to pull it into a round shape, thus qualifying for dwarf planet status, not merely an asteroid.

Today Ceres will pass through opposition, visible at magnitude 7.1 in the constellation Sagittarius. While fairly bright, the thick Milky Way star fields may make the dwarf planet difficult to spot just 3°47' west of M8, the lagoon nebula.

Comet C/2009 R1 McNaught is currently just bright enough to see without a telescope and is predicted to get even brighter. The comet is likely to brighten to around 2nd magnitude in the last days of June and the first days of July.

Reports indicate the comet is easy to spot without optical aid, and quite nice in binoculars. No tail is currently visible, creating a view much like that shown in the photo at left of Comet Lulin taken last year. Photographs do show a nice tail, which will hopefully brighten along with the comet in coming weeks.

The comet is currently crossing the constellation Perseus, low in the northeast in the last hour before dawn. Setting the alarm clock early will be necessary to see this comet. It will be closest to Earth on June 16th and 17th, at a distance of about 1.1AU (100 million miles). This is a newly discovered comet on what is possibly it's first pass through the inner solar system, thus the predictions of how bright it may get are uncertain, be prepared for surprises.

Through the month of June the comet will progress rapidly eastward though Perseus to Auriga and Gemini. For viewers in the north this will allow viewing of the comet completely through maximum brightness around the first of July. For observers in more southerly climes the comet will dip out of sight briefly during the last week of June, appearing in the evening sky during the first week of July as it passes by the stars Castor and Pollux. Here in Hawai'i, at latitude 20°N we should be able to catch the comet when it is still quite bright, just a few days after maximum.

A bright comet is always a treat, providing a show that should not be missed.

An opportunity to see a comet without a telescope occurs this month. Comet C/2007 N3 Lulin is currently in the morning sky, near the center of the constellation Libra. It is slowly brightening as it nears the Earth. Perihelion, close approach with the Sun, occurred January 10th.

The comet is expected to reach fifth magnitude in late February, just bright enough to be seen from a dark location without the use of a telescope of binoculars. Mag 5 is not very bright and will require some effort to locate and see as a small fuzzy star. The view will certainly be much better with some form of optical aid, binoculars should show the comet well.

Comet Lulin was discovered by Asian astronomers in July 2007.¹ Chinese astronomer Quanzhi Ye, a student at Sun Yat-sen University (Guangzhou, China), found the comet on images obtained by Chi-Sheng Lin (Institute of Astronomy, National Central University, Jung-Li, Taiwan) at the Lulin Observatory. The discovery was a product of the Lulin Survey, an project to map small bodies in the solar system.

Because of the geometry of our view of this comet has two tails. The odd part is that one tail points in one direction and the other is seen in the completely the opposite direction, an anti-tail. Contrary to most expectations comet tails do not point behind the comet as it moves. The dust tail is buffeted by the solar wind and always points away from the Sun from the comet's nucleus. The second tail in this case is cometary dust in the plane of the comet's orbit. As the comet orbits in nearly the same plane at the Earth this dust is seen edge-on and becomes bright enough to be visible.

The photo at the right is processed to show both tails by inverting the image. Astronomers often use inverted images to more readily show faint structure that might otherwise go unnoticed. The normal tail is seen to the right of the coma, while the dust plane anti-tail is seen to the left.

The comet should be easily observable through much of February. An ephemeris of the comet can be found at the Minor Planet Center. For finder charts and magnitude estimates go to Seiichi Yoshida's comet page for Comet Lulin.



1) Discovery announcement in IAUC8857 published by the MPC, 18 Jul 2007

After we had a nice view of comet C/2007 W1 Boattini a few months back it disappeared into the Sun's glare. It has reappeared again in the dawn sky. It should be even brighter as it is closer to the Sun, recent estimates put it at magnitude 5.5, visible to the naked eye from a true dark site, easy with binoculars.

Look for this bright comet just west of the circlet of Cetus for the first couple weeks of this month. Around mid month the moon moves into the morning sky and will interfere with observing. The comet will probably fade quickly, so the next couple weeks are your best chance to see this comet at it's brightest.