Astronomer John Griggs of Thames, New Zealand discovered this comet on 23rd July, 1902 in the constellation of Virgo during a monthly survey of the skies. Griggs could confirm its presence only after 27th July as the skies cleared. He observed the comet on 30th July, 1st and 2nd August but could not inform the authorities in time about this new, unknown comet. Astronomer James Francis Skjellerup of Cape Town, South Africa discovered a comet on 17th May, 1922. James made observations about this comet and sent notices. Two astronomers, R. T Crawford and W. F Mayer pointed similarities about the orbit of the comet but its identity could be confirmed on its return in 1927. The comet was named after its two discoverers, Griggs and Skjellerup. In 1986, astronomer Lubor Kresak pointed out that this comet was actually seen in 1808 by Jean Louis Pons.
Observations about comet 26P/Grigg–Skjellerup include:
- The comet appeared as an extremely faint nebula.
- It also appeared twice the diameter of Jupiter.
- On its discovery in 1902, a parabolic orbit was computed.
- Coma diameter was between 4 and 5 arc minutes.
The nucleus appeared at 2.6 km in diameter.
On its discovery apparition in 1902, the comet appeared very faint under cloudy skies. On its second discovery in 1922, the magnitude of comet 26P/Grigg–Skjellerup was noted at 11. On subsequent apparitions in 1977 and 1982, the maximum brightness was revealed at magnitude about 9–9.5. However, the 1997 return was unfavourable when the magnitude was 13. The comet has experienced unfavourable apparitions at magnitude 16 also in some returns.
Perihelion distance (nearest to the sun) of comet 26P/Grigg-Skjellerup is noted at 1.084 AU while its aphelion distance (far from the sun) is 4.949 AU. The perihelion and aphelion distances also change due to the strong gravitational effect of the giant planet Jupiter.
The orbital period of comet 26P/Grigg–Skjellerup is noted at 5.24 years. This period, however, increases or decreases due to the gravitational pull of Jupiter.
Comet 26P/Grigg–Skjellerup was recovered on 17th May, 1922 by astronomer James Francis Skjellerup of Cape Town, South Africa. The comet was again recovered in December 2012.
Comet 26P/Grigg–Skjellerup made twelve close approaches to the earth and four close approaches to Jupiter in the 20th century. However, the astronomical predictions stated that comet 26P/Grigg–Skjellerup may have four close approaches to the earth in the first half of 21st century along with one encounter with Jupiter.
The next perihelion date of comet 26P/Grigg–Skjellerup is 1st October, 2018. Its last perihelion was 6th July, 2013 and 23rd March, 2008.