Astronomer W H Finlay from Royal Observatory, Cape of Good Hope discovered this comet on 23rd September, 1886. The presence of the comet was confirmed by Finlay around the 27th of September, 1886. The comet was named comet Finlay after its discoverer, astronomer W H Finlay.
Observations made about comet Finlay include:
- The comet appeared faint and had no tail.
- It appeared condensed at the centre.
- The comet gained some brightness in October. It was bright at 2.5 arc minutes in October.
- Fading started by November and December onwards. The comet faded excessively and was last seen in April.
- This comet was observed as having a parabolic orbit.
The magnitude noted of comet 15P/Finlay on discovery in September, 1886, was 11. The next apparition in 1893 revealed a magnitude of about 11 while the comet appeared faint and diffused. It reached a magnitude of 6 on its 1906 return and appeared bright during the last few days of August and September. However, subsequent apparitions were very faint and were unfavourable till 1953.
The perihelion distance (nearest to the sun) of comet 15P/Finlay is noted at around 0.976 AU while its aphelion distance (far from the sun) is noted at 6.019 AU.
On its discovery, the orbital period of comet 15P/Finlay was noted at 4.32 years. During June 1910, comet Finlay passed about 0.45 AU from Jupiter, which changed its orbital period from 6.54 to 6.69 years.
Astronomer Finlay recovered the comet on 18th May, 1893. It appeared diffused and very faint. The 1899 return was unfavourable and hence, the comet was missed but it was recovered at a very favourable return in 1906. The comet 15P/Finlay appeared very bright as it reached perihelion. However, the 1913 apparition was missed but the comet was recovered again in 1919 and was again favourably recovered in 1953.
Encounters of comet 15P/Finlay include the following:
- Close encounter with Jupiter in June, 1910, which increased the perihelion distance and changed the orbital period.
- Close encounter with Jupiter in September, 1993, which decreased the perihelion distance from 1.09 AU to 1.04 AU
- Close encounter with Jupiter in May, 2004, which decreased the perihelion distance from 1.03 AU to 0.97 AU.
Next perihelion is expected around 13th July, 2021. The last perihelion of the comet 15P/Finlay was on 22nd June, 2008 and 27th December, 2014.