from the playing-cat-and-mouse-with-the-dog-star dept.
On Monday night, for a few areas of South and Central America, as well as the Caribbean, Sirius will probably briefly disappear. This will occur as a small asteroid passes in front of the star, occulting it for up to 1.6 seconds, according to the International Occultation Timing Association. (Yes, the acronym is IOTA).
In this case, the asteroid 4388 Jürgenstock will have an apparent diameter just an iota bigger than Sirius. The angular diameter of the asteroid is about 0.007 arcseconds (an arcsecond is 1/3,600th of a degree of the night sky), whereas the angular diameter of Sirius is 0.006 arcseconds. Thus, as the asteroid passes in front of Sirius, the star will briefly dim, perhaps completely, before quickly brightening again. Sirius may appear to blink once, slowly.
[...] With a diameter of 4.7km, this inner-asteroid belt object was discovered in 1964 by an astronomer named—you guessed it—Jürgen Stock. This occultation should allow astronomers a rare opportunity to better characterize the dimensions of the asteroid. It is likely to have an irregular shape—further contributing to the uncertainty about the extent to which it will block the light from Sirius.
It's not just Saturn and gas giants such as Uranus which have rings in our solar system – as a tiny dwarf planet has just been spotted with its very own.
It's the first dwarf planet beyond Neptune to be spotted with its own ring – and could prove that such rings are not uncommon in the outer solar system.
takyon: Haumea has two known moons as well as this newly discovered ring:
A stellar occultation observed on 21 January 2017 indicated the possibility of a ring system around Haumea. As published in Nature on 11 October 2017, this occultation was confirmed to be a ring, representing the first such ring discovered for a TNO. The ring has a radius of about 2,287 km, a width of ~70 km and an opacity of 0.5. The ring plane coincides with Haumea's equator and the orbit of its larger, outer moon Hi'iaka. The ring is close to the 3:1 resonance with Haumea's rotation.
Haumea is known for its extremely elongated shape, a consequence of its rapid rotation.
The size, shape, density and ring of the dwarf planet Haumea from a stellar occultation (DOI: 10.1038/nature24051) (DX)
NASA's New Horizons team will again attempt observations of a stellar occultation of 2014 MU69, provisionally nicknamed Ultima Thule. Previous observations made when the object passed in front of a background star suggested that it was a contact binary and may have a small moon:
The goal is to learn as much as possible about 2014 MU69, nicknamed Ultima Thule, which New Horizons will zoom past on Jan. 1, 2019. "This occultation will give us hints about what to expect at Ultima Thule and help us refine our flyby plans," New Horizons occultation-event leader Marc Buie, of the Southwest Research Institute in Boulder, Colorado, said in a statement.
This is not the mission team's first shadow rodeo. Last summer, scientists traveled to Argentina and South Africa for occultation observations; the Argentina crew hit the jackpot, gathering data that helped set the planned flyby distance at 2,175 miles (3,500 kilometers).
[...] Ultima Thule lies about 1 billion miles (1.6 billion km) beyond Pluto, which New Horizons famously flew by in July 2015. Scientists think Ultima Thule is about 20 miles (32 km) across if it's a single object; if it's two bodies, each component is probably 9 miles to 12 miles (15 to 21 km) long.
For over 70 years, scientists have been predicting the existence of a certain kind of object in the outer Solar System. Small in size, these potential bodies are thought to constitute an important early step in the planet formation process.
Since these hypothetical objects are only between 1 and 10 kilometres in radius (0.6 to 6.2 miles), it's tricky to spot them from where we sit. But now astronomers think they have done it. By staring at the sky for hours, they've obtained evidence of an object just 1.3 kilometres (0.8 miles) in radius, in the vicinity of Pluto's orbit. The find could finally be a representative of this proposed class of small, 'kilometre-sized' Kuiper Belt objects.
Given their small size and dimness, the objects can't be seen directly. So astronomers from the National Astronomical Observatory of Japan tried another method - occultation. This means essentially lying in wait and staring at a star, waiting for an object to pass in front of it and block some of its light. They picked out 2,000 stars, and spent a total of 60 hours observing them with the help of two small, 28-centimetre (11-inch) telescopes. The work paid off - the team found evidence of a tiny body called a planetesimal orbiting the Sun at a distance of 32 astronomical units (AU). This actually places it within Pluto's orbital range, which is between 29 and 49 AU.
[...] And the team isn't done yet. They have their sights on a much more distant prize. "Now that we know our system works, we will investigate the Edgeworth-Kuiper Belt in more detail," [NAOJ astronomer Ko] Arimatsu said. "We also have our sights set on the still undiscovered Oort Cloud out beyond that."
Also at Space.com.
A kilometre-sized Kuiper belt object discovered by stellar occultation using amateur telescopes (DOI: 10.1038/s41550-018-0685-8) (DX)