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Sunday, 22 February 2009

Comet Lulin...

Right now it is 14.37 U.T and the sky is full off Grey cloud to the West-a little bit of Sun in the South and Grey cloud right the way round the East to the North-I fear its going to be a right off tonight and I was so looking forward to seeing this Comet for the first time-maybe March may be a little clearer but that also can be a funny month and it has been known to snow then-I think I will just have to stay as optimistic as I can about this Comet as this weekend as well as into next week will be the best viewing times for this-lets hope we all get a clear window sometime to see this as it will be well placed in the evening skies in the South East and South.

Tonight the Comet will be visible from 20.50 U.T onwards and according to the Ephemeris it is +/-magnitude +4.3? (around that Magnitude) Its closest approach to the Earth is 23/24 February at 0.41 AU and being now past Perihelion at 1.38 AU from the Sun-it Transits at 02.14 tomorrow Morning and will soon Transit before midnight.


Catch Comet Lulin at Its Best!

by Alan MacRobert and Greg Bryant

Comet Lulin was showing mere ghosts of a tail and an antitail on January 19, 2009, when Michael Jaeger took this image from Austria. He used an 8-inch f/2.8 astrographic camera for exposures through LRGB filters totaling 10 minutes.
Michael Jaeger

Comet C/2007 N3 (Lulin), discovered in July 2007, is the highlight comet of this season. It's predicted to reach about 5th magnitude in late February, and as of mid-February it's easily visible in binoculars — if you have good viewing conditions. Some observers have even reported detecting it with the unaided eye in a dark, moonless sky. In telescopes and low-light images, it's showing both a dim tail and an antitail.

To find when the Moon rises and sets at your site, make sure that your location and current time zone are in our online almanac; uncheck the Daylight Saving Time box if necessary.

Below is a calendar (often updated) of the comet's doings past, present, and future (and here's an ephemeris). But the comet's brightness behavior may be a bit unpredictable, because it's on a nearly parabolic orbit that suggests this is its first visit to the inner solar system. You never know what a pristine comet might do.

The comet spent January rapidly getting higher and brighter in the morning sky as it moved across Libra. The beginning of January found it glowing at 7th magnitude, not quite as bright as predicted. It was at perihelion (closest approach to the Sun) on January 10th, at a solar distance of 1.2 a.u. (181 million km). But after perihelion Lulin continued brightening as its diminishing distance from Earth more than compensated for its moving away from the Sun.

Jan. 17: Mariano Ribas in Argentina writes: "Despite Moon interference, the comet right now is an easy target for amateur telescopes of 10 to 20 centimeters (4 to 8 inches) and big binoculars here in Buenos Aires, a city with strong light pollution (limiting magnitude about 4). Today, 1½ hours before sunrise, I saw the comet again and estimated its visual magnitude about 7.0, with a coma 3&prime in diameter and moderately condensed (DC: 5/6). But no signs of tail."

Jan. 21: "Quite visible in 10x50 binocs in spite of the crescent Moon being close," reports Amar Sharma in Bangalore, India. "20x80 binocs gave a better view as a fuzzy globular, and the 8-inch scope did reveal a condensed fuzzy coma ~4–5 arcminutes in diameter."

Jan. 22: Still only about mag 6.8 or 7.0 according to reports, about 1 magnitude below predictions.

Jan. 25: "I picked it up instantly with 10x30 binoculars this morning," says S&T's Tony Flanders, who was under a dark country sky. "It seemed comparable in overall brightness to M53 [a 7.7-magnitude globular cluster in Coma], but bigger and with lower surface brightness. In a 12.5-inch Dob at 227×, it was a very bright circular blob getting continuously brighter toward the center. I couldn't make out a stellar nucleus. I thought I saw an antitail, but it might well have been my imagination."

Jan. 30: On the other hand, in the light-polluted suburb of Arlington, MA, this morning, Flanders could not detect the comet with 10×30 binoculars. A 70mm refractor showed it dimly. Light pollution makes a big difference.

Jan. 31: "Comet Lulin is a very easy target for small telescopes and binoculars in Buenos Aires´s sky, despite our light pollution (naked-eye limiting magnitude 4.5)", writes Mariano Ribas. "With the Sun still 18° below the horizon, here in Buenos Aires the comet appears 50° over the east horizon." He estimated its visual magnitude at 6.5, "a half magnitude better than 10 days ago," using a 90mm refractor at 25×. "The coma looks asymmetrical, oval in shape, and moderately condensed (DC: 5). Still, I can´t see any of the tail (because our light pollution)."

Take a look at Jeremy Perez's visual sketch of the comet as seen in an 8-inch scope at 120×.

Comet Lulin on February 2nd, glowing at magnitude 6.5 with tail and antitail. Click image for larger view.
Paolo Candy

FEBRUARY: Peak Brightness, Peak Speed

As Comet Lulin nears Earth, it brightens and its speed across the sky increases.

February 4: "Today we were lucky enough to capture an intriguing phenomenon," write Ernesto Guido, Giovanni Sostero and Paul Camilleri. "In our images of comet Lulin, clearly visible is a nice disconnection event (DE) in the plasma tail. The DE indicates that the comet recently passed through a disturbance in the magnetic field carried by the solar wind; that destroyed the original plasma tail, creating a new one. The separation of the two ion tails is visible in our image as a kind of elongated and diffuse knot along the plasma tail." See the images on their blogsite.

February 6: This morning the comet passed close by the wide binocular double star Alpha Librae; see gorgeous photos.

February 7: Its reported magnitude is now 6.1.

Even through the moonlight on February 12th, Jim Janusz recorded both the gas tail (bottom) and dust antitail (top). He took this image from Arizona Sky Village using a 180-mm (7-inch) Astro-Physics EDF refractor with an Apogee U16-MA camera for 19 one-minute unguided exposures. He combined the exposures using the comet's nucleus as the reference point. Click image for larger view.
Jim Janusz
After moving about 1° per day at the start of February, by February 11th Lulin was creeping westward at 2° per day as it crossed into Virgo. On the night of February 15–16 it passed 3° north of Spica, while now traveling 3° per day.

The sky is dark and moonless again from about February 16th to the 28th. And the good observing times for Lulin are now more convenient: midnight or late evening rather than early morning.

February 17: Mariano Ribas writes from Buenos Aires, "I observed comet Lulin again, this time with Orion´s 90 mm refractor (25x). We still have the Moon causing some interference, but despite of its glare, the comet is a very bright object in my telescope. Using the "In-Out" method and two stars of mag. 5.7 and 5.3, I estimated Lulin´s magnitude at 5.6 . Its coma is clearly bigger (8–10 arcminutes) and more concentrated (DC:6) than just five days ago. I could not see any of its tail or antitail."

"If that brightening continues in the next days, comet Lulin will reach magnitude 5.0 or even better during its closest approach on February 24th. A good comet to celebrate the International Year of Astronomy!"

February 18: Alan MacRobert in the Boston suburbs: "It was easy and obvious to sweep up with 10×50 binoculars, looking out my bathroom window at 2 a.m. It even had the flying-saucer shape familiar from photos. Gray with barely a hint of green. The stubby antitail was fairly easy, the other tail not so much. This was with the binoculars held very steady with their homemade image stabilization."

"The Sword Comet — I have named it so!" writes Paolo Candy of the Cimini Astronomical Observatory & Planetarium in Italy. As of 0:30 UT February 20th, when Candy took this picture, the dust antitail (left) had grown in prominence to quite outdo the gas tail (right), which points away from the Sun. The small spiral galaxy below the comet is NGC 4546.

Candy used a 10-inch f/3 Baker-Schmidt Zen astrograph, and an SBIG STL 6303E camera, for L, R, G, and B exposures 3, 1, 1, and 2 minutes long, respectively.

Paolo Candy

Here's a NASA press release (Feb. 20) on the Swift satellite's observations of the comet in X-rays and the ultraviolet.

On the night of February 23rd, in a moonless sky and near its peak brightness, Comet Lulin passes 2° south-southwest of Saturn.

Lulin's closest approach to Earth, 0.41 a.u. (61 million km), occurs on February 24th, when the comet may be at a peak of magnitude 5.0. By now it's high up by late evening.

On the night of February 25th the comet goes through opposition, nearly 180° from the Sun in our sky. Will there be an "opposition effect" brightening of its dusty coma and dust tail?

And it's now speeding along at just over 5° per day! That's about 1 arcsecond every 5 seconds of time, enough to show obvious motion during a short telescopic observing session. Similarly, that's 1 arcminute per 5 minutes of time if you're using binoculars.

After that Lulin moves away from both Earth and the Sun, so it fades quickly. The evening of February 27 will see it at about 6th magnitude within 1° of Regulus. Moonlight starts interfering again around the 28th.

Weird Orbital Geometry

Strangely, as you may have noticed on the charts, this comet is traveling almost exactly along the ecliptic — backward! Could this really be just be a coincidence? The comet's nearly parabolic orbit indicates that it has never much interacted with the planets at all. Yet its orbital inclination is 178.4°, meaning that it's orbiting in the opposite direction from the planets just 1.6° from the ecliptic plane. (Manipulable 3-D orbit diagram).

Tails and Antitails

Because the comet stays nearly on the ecliptic, its tail (which points away from the Sun) aligns with the ecliptic and with the comet's own direction of motion across the sky. This is indicated by the direction the tail is pointed on the comet symbols on the finder charts linked to above.

Moreover, because Earth remains in the comet's own orbital plane, we see the comet with a very thin tail and an antitail, a spike pointing in almost the opposite direction from the main tail. Why? In three dimensions a comet's dust tail is often wide but it's always thin, confined to the comet's orbital plane. When we are in or near this plane, we can sometimes see parts of the wide, thin dust tail on opposite sides of the comet's head. We pass through most comets' orbital planes briefly. But this time, the situation will last and last.

And indeed, as early as January 7th Lulin did have an antitail, as shown in this image taken by Karzaman Ahmad in Malaysia with a 20-inch scope (image courtesy Here's another image, from Ernesto Guido, Giovanni Sostero and Paul Camilleri, taken January 8th. Here's an animation by Guido and Sostero showing the comet's motion between two images taken Jan. 16th and 17th, antitail and all. Here's a photo gallery of more.

A comet's blue-green gas tail, on the other hand, always points nearly in a straight line away from the Sun in space. Cometary gas is blown directly away from the Sun at high speed by the solar wind.

MARCH: Following Lulin Out

Comet Lulin crosses from Leo into Cancer at the beginning of March and, having passed opposition, is now better seen in the evening than the morning hours. But observers will have to contend with moonlight from about March 1st through 11th.

The night of March 5th sees the 6th-magnitude comet within 2° of both Delta (δ) Cancri and the Beehive Cluster, M44. But the Moon is also nearby.

Another conjunction occurs on March 16th when the comet, now around 7th or 8th magnitude but in a dark sky (and best seen in early evening), is 1° from Delta Geminorum.

As Comet Lulin recedes, its passage across our sky will slow. Indeed, from the end of March to the end of May (when Lulin may have faded to 11th magnitude) it will stay within a narrow, 3° strip of sky bounded by Epsilon (ε), Mu (μ), and 36 Geminorum. By May's end it will be lost in the afterglow of sunset.

Comet Lulin won't return again to the inner solar system for more than a thousand years.

Cooperative Discovery

Comet C/2007 N3 (Lulin) was discovered by Quanzhi Ye, a student (age 19) at Sun Yat-sen University in mainland China, as an apparently asteroidal object on images taken by Chi Sheng Lin (National Central University, Taiwan) with a 16-inch telescope at Lulin Observatory in Taiwan on the night of July 11, 2007. A week later, confirming images revealed the telltale presence of a coma. In China and Taiwan, the comet has been hailed as the "Comet of Cooperation."

Lulin was one of 223 comet discoveries on images taken from the ground and in space in 2007, an all-time record.

For a gallery of images and a light curve, check the Comet Lulin page on Seiichi Yoshida's Weekly Information about Bright Comets.


Postscript: What Happened to Comet Boethin?

By Greg Bryant

Another comet was expected to be visible in binoculars around this time: Periodic Comet 85P/Boethin. Discovered in 1975 by the late Rev. Leo Boethin (1912–98) in the Philippines, this comet orbits the Sun every 11 years. Or at least it used to.

Comet Boethin was recovered in 1985 and was predicted to brighten to no more than 12th magnitude during the winter of 1985–86 (when comet watchers were enjoying the buzz of Halley). However, it managed to surprise, reaching 7th magnitude in January 1986!

Did this outburst disrupt it completely? Comet Boethin was on track to return in 1997, but the poor circumstances of that return meant it could not be sighted. Nevertheless, astronomers decided in 2005 to redirect the Deep Impact spacecraft (now renamed the EPOXI mission) to study this comet, as its orbital path was ideal for the spacecraft.

In 2007 observers around the world and in space started searching for Comet Boethin, but to no avail. Not even a fragment has been found. Perhaps some tiny faint bit will be picked up by patrol telescopes in early 2009. But as of December 1, 2008, there was still no trace of it to 20th magnitude.

Fortunately, the EPOXI mission has now been redirected to the short-period comet 103P/Hartley 2. This one has been seen at four apparitions, so its orbit is secure.

This is not the first time that a periodic comet has been seen on two returns only to be lost. One example in the last century was 34D/Gale, discovered in 1927 from the inner suburbs of Sydney, Australia. It was recovered in 1938 but never seen again. Like Boethin, it too, coincidentally, had a period of 11 years.


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