Halley Absolute Magnitude Analysis (1985-1986)

Following the last return of P/Halley, I began collecting observations from around the world to conduct an analysis of the brightness of this comet. Starting with nearly 5000 visual observations obtained from August 1985 through June 1986, I began eliminating those that were in considerable error. After these eliminations, nearly 4800 observations remained. I decided to divide the observations into pre-perihelion and post-perihelion groups.

Interestingly, at the time, my computer software was not able to analyse all of the observations, so I began determining averages for each day. I also decided not to trust a daily average if based on fewer than 10 observations, so that, ultimately, only 4242 observations were used. All of these observations were corrected according to the instrument used.

To properly analyse the light curve, the existing brightness determinations were converted to absolute magnitudes---or the brightness of the comet if situated exactly one astronomical unit (slightly less than 93 million miles) from both the Earth and Sun.

The first chart represents the comet's brightness trend from August 24, 1985, to January 28, 1986. Using 2201 observations, the absolute magnitude was determined as 4.69+/-0.35, while the "n" factor was 5.0. As can be seen in the chart, this is not a straight line, but it bends early on, indicating the comet suddenly "turned on" and began brightening more rapidly than when observations began in August. (I hope to include a further set of charts on this in the near future.)

Pre-perihelion light curve

The second chart represents the brightness trend of the comet from February 23, 1986 until June 10, 1986. Using 2041 observations, the absolute magnitude was determined as 3.71+/-0.12, while the "n" factor was 3.0. This chart shows the comet's brightness to be very consistent following perihelion, although some very minor variations are noted.

Post-perihelion light curve