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:

NEAT Visibility Diagram (smaller) Visibility Table Ephemeris
LINEAR Visibility Diagram (smaller) Visibility Table Ephemeris

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

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!