Astronomical Events Calendar: A Year In Review

Out Favorite Posts from whence the beginning of this emporium began:

Stjernedannelse I Carinatåken: Star Formation in the Carina Nebula

Occultation of 136199 Eris Gives Significant Data

Ens Sidus Quod non Debet Esse: The Star Which Should not ße

Hubble Discovers Fourth Moon of Dwarf Planet Pluto
 
Hubble Transits Jupiter

Seventeenth Anniversary of Jupiter's Impact by Comet Shoemaker-Levy

New Moonlets for Jupiter - How Many Are There Now?

Conjunction of Jupiter and Phobos

Wise Infrared Gives Us A Sample of Galaxies to Come

Four Planet Dance of 2011 - What Happened?

Is Vesta the Smallest, Terrestial Planet?

Video Courtesy of NASA.

Occultation of Minor Planet 136199 Eris Gives Significant Data

Last November 6, 2010, minor planet 136199 Eris occulted the star USNOA2 0825-00375767 in the constellation Cetus. What significance does this relate to? Before this occultation, trans-Neptunian object Eris was assumed to be smaller than Pluto, its presumably larger contemporary. But now, Eris' diameter has been measured and not guesstimated, but rather an exact measurement. The video below shows the occultation, as astronomers would have seen it on that November day.

http://www.youtube.com/watch?v=HxQ0b8p4cGY&feature=player_embedded

USNOA2 0825-00375767, with a magnitude of 17.25 is a very faint star, but nothing is too dim for the Belgian TRAPPIST telescope at ESO’s La Silla Observatory to see. This event has been described by ESO as a "very rare and difficult to observe" event becasue minor planets are very small - and an occultation is even rarer. But these things do occur, for Eris will occult again in 2013, ESO reports. Astronomers first observed the star using the MPG/ESO 2.2-metre telescope at ESO’s La Silla Observatory, and a another team carefully predicted the time and what would occur during the occultation. "Observing occultations by the tiny bodies beyond Neptune in the Solar System requires great precision and very careful planning. This is the best way to measure Eris’s size, short of actually going there," explains Bruno Sicardy, the lead author.

Twenty-six places global observed the occultation and were henceforth able to determine the diameter of Eris, which had not yet been accurately determined.  Eris is a dwarft planet, today known to be the most massive, of the Kuiper Belt - the region of the solar system which contains the "remains," as astronomers call it. Eris is a dwarf planet, as well as other well-known objects such as Pluto, Sedna, and Makemake. The planet itself is magnitude 18.7 and it orbits 97.56 AU, or 9,068,768,557.0108 miles from earth. It has one moon, Dysnomia, as shown in the picture below. This moon was used to help determine the mass of Eris - which is 27% heavier than Pluto, astronomers found.

Artist's conception of Eris (with Dysnomia above)

Previously estimated was the diameter of Eris at around 3000 km (or 25% larger than Pluto), but now, the research has proved that both minor planets are essentially the same size, as Eris' predicted diameter was 2326 km. (Pluto's diameter is approximately 2300 or 2400 km, as New Horizons will find out in 2016. Pluto's obstructive atmosphere makes occultation predictions hard to accurately define).

The below picture shows trajectories of the occultation, "the three oblique solid lines show the star trajectories relative to Eris, as seen from San Pedro, La Silla and CASLEO, with the arrow pointing towards the direction of motion," as multiple authors of A Pluto-like radius and a high albedo for the dwarf planet Eris from an occultation, a paper presenting their discoveries, write. The names below are observatories in Chile where this occultation was viewed.

 
“This density means that Eris is probably a large rocky body covered in a relatively thin mantle of ice,” comments Emmanuel Jehin, who contributed to the study. “It is extraordinary how much we can find out about a small and distant object such as Eris by watching it pass in front of a faint star, using relatively small telescopes. Five years after the creation of the new class of dwarf planets, we are finally really getting to know one of its founding members,” concludes Bruno Sicardy.

The New Vesta: Dawn Spreads the Asteroid's Secrets

O beautiful Vesta! Vesta has become quite a spectacular asteroid, not only because of its beauty (as you can see in the image below), but becasue of everything Dawn has sent us so far. After Dawn reached asteroid 4 Vesta this past weekend, continual pictures and information has been sent to our planet. Vesta isn't just any old asteroid.

Isn't the protoplanet beautiful?! Dawn sure thinks so! Vesta is the second most massive object in the asteroid belt, with Ceres being the first, so it's a big deal to see such wonderful surface features on this asteroid. Ground-based telescopes have been trying to get a good picture of Vesta forever, but nothing was as good until Dawn arrived.

"We are beginning the study of arguably the oldest extant primordial surface in the solar system," said Dawn principal investigator Christopher Russell from the University of California, Los Angeles. "This region of space has been ignored for far too long. So far, the images received to date reveal a complex surface that seems to have preserved some of the earliest events in Vesta's history." No spacecraft has ever visited the asteroid belt before, so this is a first for the whole earth. NASA has accomplished much, but nothing this significant yet. It was the first space exploration group to launch a craft to visit the asteroid belt, which is very impressive.

Here, you can view Vesta's size relative to other major asteroid bodies in the asteroid belt. Click on the picture to make it larger; if you can't do that: 21 Lutetia is on top (very massive), two under that is 243 Ida and moon Dactyl, and under that is 433 Eros, just naming the famous, well-known asteroids.

As people are still in awe of Dawn's arrival after traveling over 1.7 billion miles for four years, you have to admit Dawn did make good time. Being the first spacecraft to ever make the largest propulsive acceleration of any spacecraft, Dawn made a change of velocity of more than 4.2 miles a second, on account of its high-tech ion-powered engines.

"Dawn slipped gently into orbit with the same grace it has displayed during its years of ion thrusting through interplanetary space," said Marc Rayman, Dawn chief engineer and mission manager at NASA's Jet Propulsion Laboratory in Pasadena, Calif. "It is fantastically exciting that we will begin providing humankind its first detailed views of one of the last unexplored worlds in the inner solar system."

Dawn will keep on approaching Vesta for about three weeks, looking for hypothetical moons, observing surface features and properties. NASA writes, "In addition, navigators will measure the strength of Vesta's gravitational tug on the spacecraft to compute the asteroid's mass with much greater accuracy than has been previously available. That will allow them to refine the time of orbit insertion."

Dawn will leave Vesta in July 2012, making its way to minor-planet 1 Ceres in February of 2015. More of Dawn is here, along with Dawn's 'journal.' More of Dawn at Astronomical Events Calender is Here.