Visibility conditions at 25° S, 25° N and 50°
N
for the comets
C/2001 Q4 (NEAT) & C/2002 T7 (LINEAR)
during their peak brightness around May 2004
This brief website introduces various tables and diagrams created
by D. Fischer to
visualize the viewing geometry of two potentially bright comets
that may become visible almost simultaneously in May 2004:
For each comet, the ephemeris - in 20-minute steps - was generated with the
JPL Ephemeris Generator,
the table was read off the ephemeris and the diagram was plotted
from the table. This was repeated for the three latitudes which are
representative of e.g. South Africa, the Canary Islands and
Germany.
In the diagrams, each column represents the time
interval per night during which the respective comet is at least
5° above the horizon and it is either nautical or astronomical
twilight or the Sun is even lower. One square equals one hour,
dark shading means that there is no moon at all in the sky (or at
less than 5% illumination), light shading means the moon is
present but with less than 25% illumination and no shading
means the moon is present and a nuisance.
Columns going up mean evening or all-night visibility windowns
(as are all for NEAT), columns going down mean morning visibility
windows (as are some for LINEAR). The small numbers above
some columns denote the maximum elevation at which the comet
is visible in dark, moon-free skies on that particular day. Also an
approximate light curve is provided as delivered by the JPL
Generator; it may be too optimistic, but one never knows. Neither
the maximum value nor the slope tilts are guaranteed!
The tables list only days when the comet is higher up
than 5°; what the columns mean is explained in the files
themselves. There are additional days (evident from the
ephemeris, e.g. for LINEAR at 50° North) when the
comets are just crawling along the horizon in bright (civil) twilight:
If they exceed the predictions they could still become visible
under these conditions.
What it all means is described in great detail in a
German-language page, but in a
nutshell the diagrams tell us
- that the phases of the moon are favorable for both comets,
i.e. they can be seen at the times of greatest brilliance (May 6 and
17, resp.) in dark skies and - at least at 25° S - well above the
horizon;
- that for observing NEAT alone, 25° N and S are about
equally fine, with the Southern locale better immediately around
and after peak brightness and the Northern locale better later in
the month; but
- that to see LINEAR properly you have to be at 25°
S or even farther South (and even then the elevation near
greatest brilliance in dark skies rarely exceeds 20°);
- that one can »use« the total eclipse of the moon
on May 4 to get an extra hour of dark-sky time for NEAT, but this
probably only works when you are in Africa; and finally that
- there is one interval, May 4 to 23, that incorporates the
times of greatest brilliance for both comets and even wastes
no time: From 25° South NEAT can be seen, often high, in
dark skies every evening, and LINEAR can be followed first in the
morning and then evening skies around its peak brilliance from
May 15 to 22.
Both comets have the potential in principle to become about as
bright as Hyakutake got in 1996, but even if they stay below that
level, say at +3m, they would still match
Ikeya-Zhang of 2002 which was a fine sight even under mediocre
skies. Having two such (or, of course, brighter) comets in the sky
almost simultaneously would be a very rare and probably visually
striking event, certainly worthy of a trip to a dark, southern
location with a high probability of clear skies ...
Version 1.0 of Oct. 28, 2003 - more links and news are
here!
