This is a comet to brighten rapidly around the perihelion passage. The
light curve is asymmetric and it keeps bright for a long time before
the perihelion passage.
Especially, the rapid brightening before the perihelion passage is
furious. It starts brightening about three months before the
perihelion passage, then it brightens 6-7 mag within two months and
immediately becomes visible visually. The brightness evolution turns
to slow after that, and keeps bright for about 45 days.
After the perihelion passage, it keeps bright with slow fading for a
while. But about 20 days after the perihelion passage, it starts
fading out rapidly. Not so steep as brightening before the perihelion
passage, but it fades out rapidly and returns to the original faint
state about three months after the perihelion passage.
The comet is usually almost asteroidal and so faint as 18-20 mag in
the other time.
In the Northern Hemisphere, it is observable before the perihelion
passage. In the Southern Hemisphere, observable after the perihelion
passage. The condition is better to observe in the Northern
Hemisphere.
In the Northern Hemisphere, it is observable visually when it passes
the perihelion between September and February. Especially, if it
passes the perihelion in mid or late December, it approaches to the
earth and brightens up to 6.5 mag. The condition is also excellent to
observe. On the other hand, it is not observable in its bright time
when it passes the perihelion between April and August.
In the Southern Hemisphere, it is observable visually when it passes
the perihelion between January and August. However, the maximum
brightness becomes 8 mag at best, much fainter than the Northern
Hemisphere. On the other hand, it is not observable in its bright time
when it passes the perihelion between September and December.
Kazuo Kinoshita's calculation revealed no significant change of the
orbit from mid 18th through the end of 21st century.
However, the brightness of the comet has been declining. At its
discovery in early 19th century, it was brighter than now by 4 mag. It
reached to 3.5 mag at best and visible as bright as Andromeda Galaxy
with naked eyes. Now it reaches to 6.5-7 mag at best.
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