A Small Asteroid Will Cover a Supergiant Star

Betelgeuse stands out as one of the celestial marvels, ranking among the top 10 brightest stars that grace our night sky. With a diameter nearly 8000 times that of the Sun and radiating luminosity exceeding 100,000 times, this stellar giant is at a secure distance of approximately 650 light years from Earth. Positioned within the prominent Orion the Hunter constellation, Betelgeuse’s presence makes it a captivating spectacle for astronomers and stargazers alike.

In 2019 and 2020, this red star surprised astronomers worldwide by undergoing a period of dimming that lasted for several months. Once again, we were looking forward to a small decrease in brightness, but this time it was because of an asteroid passing by. It was another peculiar event that would only last a couple of seconds.

This phenomenon is called occultation, a well-established concept in Astronomy. It’s when one celestial body hides behind another for a little while. If an observer is in the right spot and at the right time, they will notice that the object being hidden gets a bit dimmer for a short while. This could happen suddenly or gradually. For instance, the Moon could hide planets and stars, planets could eclipse stars, and passing asteroids might briefly cover up stars.

Given the abundance of asteroids, it’s likely that someone on Earth may witness one of them eclipsing a star on any given night. However, due to their relatively small size and the often faint luminosity of the stars they conceal, such occurrences are typically observable only with sophisticated and highly sensitive equipment.

Examples of star occultation by asteroid record. A small eclipse lasting a few seconds can tell a lot about the asteroid and the star (The Planetary Society / The Unistellar Network).

With the incredible view of the vast celestial panorama from our Earth, it’s not every day that we get to witness asteroids passing in front of prominent stars. That’s why the upcoming event on December 12th has got astronomers buzzing with genuine excitement.

On this day, observers located within certain countries bordering the Caspian Sea, Turkey, southern Europe, traversing the Atlantic Ocean, and reaching southern Florida (USA) will have a remarkable opportunity.

The second participant in this occultation is 319 Leona, an asteroid first identified by the French astronomer Auguste Charlois in 1891 at the Nice Observatory in southeastern France. Charlois, one of the most prolific asteroid discoverers of the 19th century, added Leona to his list of achievements as the 25th of the 99 asteroids he discovered during his distinguished career.

Leona’s diameter is estimated to be in the range of 49 to 89 kilometres, based on observations with infrared instruments and data from previous occultations. The margin of error in these measurements should improve as new occultations happen since each event gives us a chance to make more accurate observations.

Furthermore, this phenomenon is expected to greatly contribute to our comprehension of Betelgeuse brightness distribution across its stellar disk. Given the star’s distinctive behavioural patterns, the occultation holds dual significance, offering insights not only into Betelgeuse but also into the characteristics of the intervening asteroid.

Scheduled between 1:08 am and 1:26 am GMT/UTC on December 12th within the specified regions (note that for observers in Florida, the occultation becomes apparent before the end of December 11th), astronomers worldwide are gearing up for this event. Observatories in the predicted occultation zone are organising campaigns, welcoming both amateur astronomers and the general public to participate in observing and documenting this fascinating celestial phenomenon.

The collaboration between professional and amateur astronomers has proven to be very effective in uncovering new findings, particularly in the field of asteroid research. They have succeeded in collecting important data, such as determining the size and presence of moons associated with specific asteroids, by documenting occultations. This collaboration even resulted in the discovery of a ring system circling the asteroid Chariklo back in 2013.

Below, you’ll find a guide that will facilitate your participation in this captivating celestial event:

• If you’re curious about what happens during an occultation, we recommend watching this video recording captured in 2010 by the Samford Valley Observatory in Australia. This footage captures the asteroid Leona obscuring a faint star. Keep an eye on the star positioned near the video’s centre.
  Observe the stopwatch, including fractions of seconds, emphasising the critical importance of precise timing in recording occultations for scientific purposes. These fleeting seconds are invaluable, offering profound insights into both the characteristics of the asteroid and the occulted star!
• Record the upcoming occultation with your smartphone cameras. To use an accurate chronometer during the recording, consider utilising the Occult Flash Tag app.
• David Dunham, a representative from the International Occultation Timing Association (IOTA), has recently hosted this presentation, offering updated insights into the occultation and specifying the regions where it will be observable.
• For comprehensive details and organised observational campaigns across various countries, visit the IOTA website.
• This edition of the Journal for Occultation Astronomy features a thorough article, with detailed maps of the regions for optimal observation of the phenomenon.
• Steve Preston’s webpage stands as a key online resource for asteroidal occultations, offering maps and sky charts pinpointing the precise locations of these celestial events.

If you succeed in contributing valuable data to scientific endeavours by recording this rare phenomenon, please share your findings with us. We’re eager to showcase your contributions on our social media platforms!

Wishing you the best of luck and clear skies in your astronomical challenge!

See also:
LEARN – How can we characterise asteroids?