Comet Corner

By Don Pearce

 

This is a periodic update on observational aspects of visible comets.

April 3, 2009

 

(Editorial note: Currently, the Comet Corner will only report on either the brightest or most interesting one or two comets each month)

 

Comet C/2007 N3 (Lulin) was discovered by two Chinese astronomers and named for oneís observatory in Taiwan. It was an inbound long-period comet that reached perihelion on Jan. 10th (1.21 AU), and then reached closest approach to Earth on Feb. 24th at .41 AU. Currently, Lulin is in Gemini at about 9th magnitude.It was moving fairly rapidly (as it approached the Earth), but has slowed down, dramatically, as it recedes from the Earth (and Sun) and its motion in the sky has slowed to the point that it will appear to begin retrograding around April 23rd , spending most of the rest of 2009 in Gemini. Lulin has an extreme retrograde orbit, which places it almost in the plane of the ecliptic; in fact, its orbit even crossed the ecliptic in late Feb. This had given rise to the ongoing appearance of an anti-tail, which ended about February 26th. (It should be noted that the requirement for the appearance of an anti-tail require that the Earth pass through the cometís orbital plane, which, in this case, happen to almost coincide).Lulin peaked at magnitude 4.8 around Feb. 23rd, close to the date of closest approach to the Earth. In fact, there was a sequence of significant events all within a short period of time.First, Lulin had its closest approach to the Earth at around 11pm (CST) on 2/23. Secondly, at around 1 am on 2/25 Lulin crossed the ecliptic going from N to S. Thirdly, at about 2 am on 2/26 the comet was in opposition to the Earth.The changing geometric perspective has given rise to the very beautiful and changing tail structure. The cometís coma had a very distinct greenish color, due to the abundance of cyanogen and diatomic carbon. Its nucleus may be tumbling with a corkscrew motion.Currently, Lulinís orbit will evolve into a long elliptical orbit (leading to an orbital period of about 42,000 years), even though it currently has a hyperbolic orbit.Lulin is still well placed for observing in the evening sky, currently setting about 2 am, and it will still be up until about midnight by the end of April.

 

Comet C/2009 E1 (Itagaki) was discovered on March 14th by Koichi Itagaki with an 8-inch F/3 reflector plus CCD from Yamagata, Japan. Although originally projected to peak at about 10th mag. when it reaches perihelion on April 7th at .6 AU, it already is about 8th mag., but, probably wonít get much brighter. Itagaki is currently about to enter Triangulum (from Aries) and will end the month of April in Pisces as it moves northwesterly. On April 13th it will pass less than two degrees from M 33.

††

Current comet magnitudes (April 3) and observable region (April 1)

†† Comet††††††††††††††††††††††††† Magnitude†† Trend†† Observable††† When visible
†† Itagaki (2009 E1)†††††††††††††††††† 8††††† steady70 N to 15 Nearly evening
†† Lulin (2007 N3)†††††††††††††††††††† 9††††† fade††† 70 N to 55 Sbest evening†† 
†† Christensen (2006 W3)†††††††††††††† 9.5††† bright70 N to5 Nmorning
†† Cardinal (2008 T2)†††††††††††††††† 10††††† bright70 N to 20 Sbest evening
†† 144P/Kushida†††††††††††††††††††††† 10††††† fade††† 70 N to 50 Sevening
†† 67P/Churyumov-Gerasimenko††††††††† 10††††† fade††† 65 N to 15 Searly evening
†† Siding Spring (2007 Q3)††††††††††† 11††††† bright35 N to 80 Sevening
†† 22P/Kopff††††††††††††††††††††††††† 11††††† bright45 N to 80 Smorning
†† McNaught (2008 A1)†††††††††††††††† 11.5††fade††† 70 N to 20 Nmorning
†† 116P/Wild††††††††††††††††††††††††† 12††††† steady70 N to 40 Sbest evening
†† 29P/Schwassmann-Wachmann†††††††††† 12 ?††† varies70 N to 35 Sevening
†† Broughton (2006 OF2)†††††††††††††† 12††††† fade††† 70 N to 25 Sevening
†† LINEAR (2007 G1)†††††††††††††††††† 12.5††† fade††† 20 S to 80 Sevening
†† 19P/Borrelly†††††††††††††††††††††† 13††††† fade††† 70 N to 20 Sbest morning
†† 65P/Gunn†††††††††††††††††††††††††† 13.5††† steady70 N to 45 Sall night
†† 210P/Christensen (2008 X4)†††††††† 14††††† fade††† 65 N to 55 Sbest morning
†† McNaught (2006 Q1)†††††††††††††††† 14††††† fade††† 70 N to 35 Sbest morning