Great views from Namibia (Image: Christophe Lehenaff/Getty Images/Photononstop)

This rock’s got some bling. A star that is about to wink out over Africa will give us a good look at the first known asteroid with rings.

Last month, astronomers described icy rings around the asteroid 10199 Chariklo. They were found during an occultation, when the asteroid crossed in front of a star from Earth’s perspective. Seen from South America, the star’s brightness dipped in a distinctive pattern, indicating a set of sharply defined rings.

At 23.14 UTC on 29 April, Chariklo will pass in front of another star, an event that will be visible from a narrow path across South Africa, Namibia and possibly Botswana.


The star is the brightest one that Chariklo will cross in 2014, and it should be easy to spot with amateur telescopes. Some of the scientists who helped find the rings are also hoping to watch the event from regional observatories, such as the South African Astronomical Observatory in Cape Town and the International Amateur Sternwarte in Namibia.

Clear skies

The star will seem to vanish for up to 19 seconds, and records of where people saw the event and how long it lasted at their location will be compiled to recreate the asteroid’s “shadow”. This information could help better pin down Chariklo’s size and shape, perhaps giving clues to its composition.

The rings will cast a much wider shadow across southern Africa, visible 300 kilometres out from the centre of the asteroid’s path. “With the right equipment, I would hope an observer could record some variation in the star’s light as the rings occult the star,” says Steve Preston, president of the International Occultation Timing Association. That could tell astronomers more about the rings’ orientation, and perhaps offer clues as to how they have survived.

For instance, the gravitational pull of a “shepherd” moon could be corralling the rings into a tidy shape, akin to what happens in the rings around Saturn and Uranus. Such an orbiting body would cause a further dip in brightness that may be noticeable as the asteroid slips in front of the star.

“It’s a good occultation, as there are major observatories in South Africa and places in the Namibian desert where it is good to observe from,” says Colin Snodgrass at the Max Planck Institute for Solar System Research in Göttingen, Germany, a co-discoverer of Chariklo’s rings. “And the skies will almost certainly be clear.”