Mark Kidger
March 16, 1997
I am currently updating the light curve once or twice a day, as new data arrives and time permits. The latest light curves at
http://www.iac.es/comet/obser.html
are now based on over 800 observations and show the remarkable behaviour of this comet. I will add tail length and coma diameter plots next week. Some tail estimates are getting up to around 1AU true length for the gas tail, although the majority of observers are seeing a tail around 80-100 million kilometers long at dark sites. Some time this week I'll add in another data file which will increase coverage of the comet's light curve especially for last Autumn.
As you can see when you look at the light curves the comet is continuing the amazing linear rise in brightness when its brightness should have almost topped-out by now. As of today there is no sign that the brightness increase is flattening out, which is consistent with the observations that the comet's gas and dust emission is increasing faster than could be explained by the decrease in heliocentric distance.
At present Hale-Bopp's absolute magnitude is increasing rapidly (if one assumes that the increase in brightness that we are seeing is caused by an increase in absolute magnitude). From -0.5 about two weeks ago it has gone up to about -1.2 and is closing in on the second brightest absolute magnitude ever recorded (the comet of 1577, sometimes called Tycho's Comet, which had and absolute magnitude around -1.8).
If this linear brightening were to continue to perihelion, Hale-Bopp would easily go past magnitude -2 (and then start to rival Comet West which was only poorly visible when at its very brightest), although this rate of increase surely cannot continue for much longer. Even if the light curve starts to flatten-out, as it should do, we can expect a maximum around magnitude -1.5 at maximum and certainly the comet will be no fainter than -1, although no comet should ever be relied-upon to behave itself beyond the last datum point.
No comet that I can remember has ever shown this kind of light curve behaviour.
Some time we will need to work out why the comet is behaving this way but, for
the moment, its a question of sitting back and enjoying it. Certainly we are
a long way from the predictions late last Summer that the maximum might only be
magnitude +3 and no brighter than +2.
Comet Hale-Bopp Home Page