At the end of this month, stargazers may have the chance to enjoy a spectacular meteor shower in the night sky.
The reason is the 73P/Schwassmann-Wachmann 3 comet, which was discovered in 1930 when it passed by at 9.2 million kilometres from the Earth, and is now split into numerous fragments. At that time it was never bright enough to be visible with the naked eye, only through good binoculars or a telescope.
On the night of 30 May, it will be the first time the Earth and the trail of debris ejected by the comet in 1995 have crossed paths since the fragmentation. However, nobody knows exactly where the meteoroids have extended, so it is difficult to predict how many will be visible. The final intensity of the meteor shower will depend on whether the debris has spread far enough ahead of the comet.
This comet orbits the sun every 5.4 years. After 1930 it disappeared for quite a while. In fact, between 1935 and 1974, it came and went eight times without being seen and wasn’t visible again until March 1979. We missed its following return in January 1985, but saw it again in early 1990.
Astronomers expected the comet to make another uneventful return in the autumn of 1995. But in early October, the Central Bureau for Astronomical Telegrams suddenly began receiving "numerous reports from observers around the world of independent discoveries" of a comet with the naked eye, low in the western evening twilight and sporting a 1-degree-long dust tail. It was 73P/SW3, Space.com reported.
That was surprising because the comet was never closer to the Earth than 196 million kilometres in 1995 and should only have been visible through quite large telescopes. Still, there it was, shining 400 times more brightly than expected. The reason, as the European Southern Observatory at La Silla in Chile, discovered, is that its diminutive core had broken into four parts.
The comet was still quite bright on its following visit in the autumn of 2000, showing that two of the fragments detected in 1995 had returned, along with a new one, which probably broke off on its way back.
In the spring of 2006, the disintegrating comet made its return appearance, initially showing at least eight remnants, with some of the fragments themselves forming sub-fragments.
On 18 April 2006, the Hubble Space Telescope recorded dozens of fragments. Between 4 and 6 May, the Spitzer Space Telescope photographed the comet and, using its infra-red imaging camera, observed 45 of 58 fragments. In total, the 73P/SW3 finally divided into more than 68 fragments, and during its last appearance in March 2017 it showed signs of continuing to break up and was shedding more pieces every time it returned through the inner solar system.