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 one’s 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 comet’s 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 comet’s 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, Lulin’s 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 won’t 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 steady 70 N to 15 N early evening
· Lulin (2007 N3) 9 fade 70 N to 55 S best evening
· Christensen (2006 W3) 9.5 bright 70 N to 5 N morning
· Cardinal (2008 T2) 10 bright 70 N to 20 S best evening
· 144P/Kushida 10 fade 70 N to 50 S evening
· 67P/Churyumov-Gerasimenko 10 fade 65 N to 15 S early evening
· Siding Spring (2007 Q3) 11 bright 35 N to 80 S evening
· 22P/Kopff 11 bright 45 N to 80 S morning
· McNaught (2008 A1) 11.5 fade 70 N to 20 N morning
· 116P/Wild 12 steady 70 N to 40 S best evening
· 29P/Schwassmann-Wachmann 12 ? varies 70 N to 35 S evening
· Broughton (2006 OF2) 12 fade 70 N to 25 S evening
· LINEAR (2007 G1) 12.5 fade 20 S to 80 S evening
· 19P/Borrelly 13 fade 70 N to 20 S best morning
· 65P/Gunn 13.5 steady 70 N to 45 S all night
· 210P/Christensen (2008 X4) 14 fade 65 N to 55 S best morning
· McNaught (2006 Q1) 14 fade 70 N to 35 S best morning