15 December 2020
Perihelion Distance (q)
Aphelion Distance (Q)
Click for NASA orbit diagram
Hills Observatory: 1 January 2013 to 26 May 2020
This comet was discovered by Donald E. Machholz (Colfax, California, USA) on 13 August 1994
with a 0.25-m reflector. He estimated the brightness as magnitude 10 and said the coma
diameter was 3 to 4 arc minutes across. Machholz added that the comet was diffuse with little
condensation. The comet was confirmed in twilight by T. Kojima (YGCO Chiyoda Observatory,
Japan) on April 13.80. He said the comet was diffuse with condensation.
The first orbit was determined by S. Nakano (Sumoto, Japan) and was published on 15 August
1994. It was parabolic and indicated a perihelion date of 13 September 1994, a perihelion date
of 0.757 AU, and an inclination of 15 degrees. The first elliptical orbit was computed by Daniel
W. E. Green of the Central Bureau for Astronomical Telegrams and was published on 23 August.
He found a perihelion date of 17 September 1994, a perihelion distance of 0.753 AU, and an
orbital period of 6.81 years. By late September, further observations generally confirmed this
early short-period orbit, although the period had been revised to 5.23 years.
Michael Jäger (Vienna, Austria) reported his discovery of a second comet just 48 arc minutes
from comet Machholz 2 on 28 August. He said it appeared to have the same motion as Machholz
2 and estimated the magnitude as 11. This comet continued being observed during the days that
followed. A third object was independently found on 2 September by Petr Pravec (Ondrejov
Observatory) and on 3 September by Wayne Johnson (Anza, California, USA). It was 43 arc
seconds from the second object and about 1 magnitude fainter. Fourth and fifth objects were
found by Pravec on 4 September and confirmed elsewhere. Letter designations were assigned to
the 5 comets on 21 September. The primary comet was the most westward and was designated
"A". Working eastward, "B" was the fourth comet found, "C" was the third comet, "D" was the
second comet, and "E" was the fifth comet. Interestingly, Pravec reported that CCD images
obtained on 5 October indicated "D" exhibited two condensations within its coma.
Although initial brightness estimates indicated the comet would barely exceed magnitude 10, the
comet continued brightening as the various components were discovered, probably indicating
increased reflectivity because of excess dust output as a result of the breakup. The main comet's
maximum magnitude peaked at about 7 during the first days of September.
The comet was recovered by R. H. McNaught (Siding Spring Observatory, Australia) on 3 August
1999. The comet then appeared stellar, with the magnitude estimated as 20.3-20.8. Calculations
revealed this was comet "A", as designated from 1994, with the predicted orbit requiring a
correction of only +0.8 day. A search for other components failed to reveal anything.
The comet brightened slowly and finally came within range of the large amateur telescopes at the
end of October and beginning of November, when estimates of the brightness were near 12.
Interestingly, McNaught reported a single image obtained at Siding Spring on 17 October showed
component D had appeared. This was confirmed by Jäger and Gerald Rhemann on October 27.
Jäger and Rhemann said D was running about one magnitude fainter than A.
At the end of November both components A and D were near magnitude 12, with a diameter of
2 arc minutes. As December progressed, component A brightened, while D began to fade.
Around mid-month component A was near magnitude 11.5, and it had brightened to around 10
by month's end. Component D remained near 12 until near mid-month at which time it dropped
to 13. It was close to 13.5 as the month ended. As 1999 ended, component A was about 5 arc
minutes across, while D was typically estimated as 3-4 arc minutes in diameter.