What is Wirtanen's background?

Discovery and Subsequent Apparitions

Wirtanen was discovered on Jan 17, 1948 by Carl Wirtanen at the Lick Observatory. Since then, it has been observed on every apparition except for its 1980 passage, when it remained within 20° of the Sun for months around perihelion.

Encounters with Jupiter

At aphelion, Wirtanen approaches Jupiter's orbit. Over the last few apparitions (and future ones), it has been close enough to Jupiter to experience a number of significant perturbations that have caused its orbit to evolve.

Date Distance from Jupiter Change in Perihelion Distance Change in Orbital Period
Dec 31, 1912 0.53 AU 1.62 →  1.43 AU 6.81 →  6.32 yr
Dec 25, 1923 0.52 AU 1.43 →  1.61 AU 6.32 →  6.65 yr
Apr 10, 1972 0.28 AU 1.61 →  1.26 AU 6.65 →  5.87 yr
Feb 26, 1984 0.47 AU 1.26 →  1.08 AU 5.87 →  5.50 yr
Nov 25, 2042 0.56 AU 1.06 →  1.22 AU 5.49 →  5.78 yr

It is not known if this is Wirtanen's first foray this close to the Sun, but if it is, then the decrease in perihelion distance means that it has been experiencing more intense heating in the past few orbits than it has before.

Recent and Upcoming Apparitions

Wirtanen's current orbital period is near 5.5 years, which means that its apparitions alternate between good and bad with respect to the Earth. The 2013 apparition was very poor, and only a few distant measurements were obtained in 2014, after its perihelion passage. The 2024 apparition will be equally poor.

On the other hand, the 2018 apparition is excellent, with the comet making a very close approach (0.077 AU) to the Earth. This encounter occurs just a few days after perihelion, so the comet is likely to be visible to the naked eye for up to several weeks. Furthermore, the approach occurs near opposition, which means the comet will be visible for many hours during the night, from both the northern and southern hemispheres. This presents a great opportunity to study this object. For more information, see the 2018 Apparition page and the Geometric Conditions page.

Many thanks to Gary Kronk and his Cometography books for contributions to this history.