Sunday, October 30, 2011

Jovian Dual-Shadow Transit of October 31, 2011

Remarkable was the dual-shadow transit on October 24. But, there is yet another and unfortunately the final dual-shadow transit of Jupiter in 2011. October 31 will bring us one more "astronomical morsel" and this one will be presumably about the same as the last: Io will transit just beneath the waistline of Jupiter, and Ganymede at the exact bottom of the king of the planets. Both of the shadows will be cast on the planet for only sixteen minutes, from 18:10 to 18:26 UT. This will be during the day for Washington DC, at approximately 1:10 to 1:26 EDT. Although this is rather sad, the eastern world will be able to witness the last Jovian dual-transit for the great year of 2011. A comprehensive photo shoot (courtesy of The Transits Page) is shown at the end of this article. Below is a picture of the Jovian moons at 00:00 UT on October 31, 2011, or at 8:00 October 30, for us here in EDT.

Image Credit: Transits Page; Text entered by AstronomicalEventsCalendar

Callisto beautifully rests on top of the planet, as it's orbit appears to be above the planet, we must remember that these orbits are three dimensional - and that since Jupiter is titled towards us, it looks like Callisto orbits above. Sense Perception! Concerning the transit, you can see Io and Ganymede - Ganymede will swoop down and catch up to Io (they are not actually that far apart in the two-dimension scale, becasue of their orbits, but they appear to be far apart). The dual-transit itself will start at 17:46 UT and end at 18:22 UT, lasting only 36 minutes. If you can remember, this is very shorter than the October 24 transit.The next picture below concerns itself right before the transit - at 16:00 UT. Ganymede and Io are now very noticeable together.

Image Credit: The Transits Page; Text entered by AstronomicalEventsCalendar

If you're wondering what a Jovian dual-sahdow transit is? Look no further - Here, we can clarify the terms of dual-shadow transit, and dual-transit, becasue both can happen at the same time - the October 24 and 31 transits are great examples of these (among others). A dual-shadow transit occurs when two shadows of moons travel across the surface of Jupiter together (and yes this can also happen on any other planet with two or more moons, etc.), and then, when the two moons travel together, it is called a dual-transit. (The difference is just either the shadow or moon), but both have to cross Jupiter (or any other planet, etc.) at the same time. You can read more about Jovian transits in our last transit: October 24.

You can view images at the Jovian Dual-Transits Emporium, run by me, of course. 

Thursday, October 27, 2011

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.

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.

Wednesday, October 26, 2011

Jupiter at Opposition October 29, 2011

This October 29, Jupiter will reach the closest to earth, making observation excellent on cloudless nights. It is the closest approach the planet will ever get to earth between the dates of 1963 and 2022, so now is the time to study the king of the planets. On this day, earth will pass directly in between the Sun and Jupiter, making Jupiter the brightest, becasue it's closest. Although on this date the planet will be the brightest, it will be more noticed in November due to its movement in the sky. Currently, this planet is about 35 degrees from the horizon in the east, and the Galilean moons are very easy to view - even with binoculars.

Jupiter, taken by the Cassini space probe

Shining at magnitude -2.9, Jupiter is in Pisces and is 49.7 arc-seconds across. At 18:44:21 UT, Jupiter is at greatest opposition, being 3.96976 AU (Astronomical Units, distance of earth to sun, or 93 million miles) from the planet. This is 369,012,245.45797 miles away, respectively. What times can I see Jupiter? This is an excellent question - Jupiter is at opposition, therefore meaning that Jupiter will be visible all night. (Even when the moon is full, Jupiter is still bright and beaming!).

Jupiter, as seen by the Cassini space probe (the back spot on the planet is Europa's (moon) shadow)
Where Jupiter is in relation to the constellations

Viewing the Galilean Satellites

As some readers might note, Jupiter's moons are a big point of interest here at Astronomical Events Calendar. (We have even a blog dedicated to them). With just simple binoculars, you can make out all for of the Galilean moons: Io, Europa, Ganymede, and Callisto. The past few nights, I have seen the moons fairly easily and you can too. But how do I know which moon is which? As a general rule of thumb, the innermost moon is Io, the second Europa, then Ganymede, and Callisto's orbit is the farthest; all these moons, though, are at different positions and therefore hard to discern without a very strong telescope lens (you can tell by color, then) or a map of where the moons will be.

Sky&Telescope provides a "wobble*" map, showing where these moons will be in relation to Jupiter. Below are some pictures of where these moons will be positioned on certain dates.

Jupiter will be visible in the sky through the rest of 2011, but note that it will be getting dimmer. Note that Jupiter will be the closest to earth only this year until 2022 again, and keep an eye on the glorious moons of our favorite planet: Jupiter!

*for November

Monday, October 24, 2011

Occultation of Mercury: October 28, 2011

The third and final occultation of 2011, Mercury's occultation this October 28, 2011 will be an astronomical treat for those in Australia, New Zealand, & southern Oceania. Although it was a true fact that each of these occultations this year (2011) were poor to view, 2012 brings yet another smorgasbord of events, as listed at the end of this article.

"It will be observable after sunset from French Polynesia," the Transits Page writes in correspondence of the event. From there, the whole southern Oceanic hemisphere, centered in Australia & New Zealand, will see Mercury occult, right through the center of the Moon. This is a "central one," referring that Mercury will pass through the center of the Moon. Basic information is below.

Greatest Occultation = 2011-Oct-28 02:11:32 TT
Occulted Planet = Mercury
Occultation Series = 7560
Member = 1 of 1
Elongation from Sun = 18° E
Moon illuminated fraction = 2 %
Lunar Magnitude = -5.9
Planetary Magnitude = -0.3
Gamma = -0.21966
Gr. Longitude = 158° 31.4' E
Gr. Latitude = 32° 43.0' S
Gr. Duration = 94m 10.3s
ΔT = 66.64s

Credit: the Transits Page

This occultation occurs in the 7560 series (similar to the Saros of eclipses), and will be the best to view. Mars' Tahitian occultation in July, and Venus' Mediterranean occultation in June both occurred with poor lunar conditions, but the moon will only be two percent illuminated this time! Mercury will pass swiftly - starting on the 27th of October at 23:56 UT and ending on the 28th at 04:24 UT - four hours and twenty-eight minutes total. Below is a picture of Mercury's entrance and exit passage at the green dot in the above picture (in between Australia and New Zealand).

Credit: Transits Page
Local Circumstances—Greatest Occutation

Longitude = 160° 42' 51" E
Latitude =  32° 08' 34" S
Elevation = 0m.

Greatest Occultation = 2011-Oct-28 02:16:20.4 UT
Altitude =  77.8°
Azimuth = 353.7°
            Calendar Date and Time          Planet           Sun     Limb
                Universal Time         Azi    Alt    PA      Alt      PA

Ingress    2011-Oct-28 01:29:10.9 d   39.2°  74.8°  102.4°   69.7°  290.8°
Egress     2011-Oct-28 03:03:56.2 b  311.7°  72.9°  287.7°   56.0°  290.4°

Duration    94m 45.3s

Mercury's occultation is hoped to be great - so watch the Moon, if you live in the area of occultation!

Friday, October 21, 2011

Extragalactic and Nearby Comet Storms

Just recently, the Spitzer Telescope of NASA has detected signs of a comet storm in the exoplanetary system of Eta Corvi, respectively (and presumably) in the constellation Corvus, the crow. These frosty masses of ice and stone fling themselves into the members of this system, creating much dust and possibly signs of water. (More presumably, you've heard about the water detected in the stellar disk of TW Hydrae, correct? Peculiar to note is the close similitude of the name as it is related to water!) To this fact, astronomers strive to believe that life will form on in this system, becasue that's what they think about us. NASA is always trying to find new life in our universe - we should be content with the life we have here.

Using special instruments that scientists applied Spitzer with (mainly the infrared detectors), astronomers are starting to analyze light that is recieved from the stellar dust emitted by Eta Corvi. "Certain chemical fingerprints were observed, including water ice, organics, and rock, which indicate a giant comet source," NASA writes. If you noted the Almahata Sitta meteorite that fell in fragments in 2008, you might remember the close similarities between Eta Corvi and meteorite Almahata Sitta. The dust from both of these 'objects' are very similar and NASA implies that the common "birthplace" is the same in our universe; saying that Almahata Sitta came from, or is just coincidentally resemblant to Eta Corvi's dust. (Astronomers assume that this meteorite comes from the Kuiper Belt, discussed below).

A piece of 8TA9D69, or Almahata Sitta in the Sudanese desert. Credit: APOD

Spitzer also located a rather large ring of frigid dust (discovered in 2005), respectively in location at the far edge of the system. The report does note how far this 'edge' is assumed to be: 150 AU, or approximately 8.390111903e-25 light years, and they believe that this location is a "reservoir" for icy, cometary objects - making a correlation between our own solar system. One of the most fascinating places in our solar system is the Kuiper Belt, which is closely compared to Eta Corvi's dust ring. The Kuiper Belt is home to thousands of icy bodies, including Pluto, Eris, and Sedna to name a few. Our minor planets page discusses these - picture section.

So, in conclusion, astronomers believe that similar to Eta Corvi's, icy objects from the Kuiper Belt is what impacted many minor planets - such as lunar craters and other observable ones. Although their views are evolutionary, it is still a good hypothesis yet. "We think the Eta Corvi system should be studied in detail to learn more about the rain of impacting comets and other objects that may have started life on our own planet," said Carey Lisse, senior research scientist at the Johns Hopkins University Applied Physics Laboratory in Laurel, Md., and lead author of a paper detailing the findings. The findings will be published in the Astrophysical Journal. Lisse presented the results at the Signposts of Planets meeting at NASA's Goddard Space Flight Center in Greenbelt, Md., Oct. 19.

An artist's concept of a comet storm around Eta Corvi. Image credit: NASA/JPL-Caltech

Another thing to note, the Orionid meteor shower is peaking, specifically October 22. "Although this isn't the biggest meteor shower of the year, it's definitely worth waking up for," says Bill Cooke of the NASA Meteoroid Environment Office. "The setting is dynamite." Over the past few days, more than fifteen metoers will slash across the night sky, but the most dramatic ones are at dusk.

A map of the morning sky on Saturday, Oct. 22nd at 5:30 a.m. local time, viewed facing southeast. Click to view a larger, more complete map.

Wednesday, October 19, 2011

Jovian-Dual Shadow Transit for October 24, 2011

After having such a prolific season of simultaneous Jovian dual-transits last May-June, it will be hard to accept the fact that we have only two more this 2011 season: October 24, 2011 and October 31, 2011. Each transits are an exact week apart (although times differ) and both are dual-shadow transits. Io and Ganymede both partake in each event, as their orbits must be aligned perfectly just for this week. According to Simultaneous Transits of Galilean satellites and their shadows across Jupiter during 2011, a paper that lists each of dual-transit phenomena in full (can be found here), the October 24 dual-transit is the longest of the two (the other being October 31, respectively) with both moons transiting over 1 hour 18 minutes, with both shadows on the planet over the span of 58 minutes. A comprehensive photo shoot (courtesy of The Transits Page) is shown at the end of this article.

Image Credit: Transits Page; Text entered by AstronomicalEventsCalendar

Looking at the above image, we see the Galilean moons on October 24, 2011 at 00:00 UT (times forth are Universal Time, or UT). The transit begins 14:22 UT and ends comprehensively at 15:20 UT - a rather long dual-transit at 1 hour and 28 minutes, although the longest was on January 10, 2011 (2 hrs & 15 min). The next image shows the Jovian satellites at 14:00 UT, on the same date. Note how close Io and Ganymede are, and the shifting of Callisto and Europa.

Image Credit: The Transits Page; Text entered by AstronomicalEventsCalendar

In the above image, you can see Io and Ganymede about to enter transit. Callisto has shifted further away from Jupiter as it completes its orbit, and Europa is shifting down, as its orbit is completed. During transits with Ganymede, because of Ganymede's orbital eccentricy, it orbits near the south pole of Jupiter, making transits involving it shorter than transits with Europa. Europa and Io orbit very closely around the belt line of Jupiter, making dual-transits more facile; Callisto only dual-transited once this year, on January 10 (which was the longest, partially becasue Callisto is the farthest moon, and orbits slower than Europa, who shared the transit. Other than that, only Io transits the rest of 2011, with either Ganymede or Europa, see for yourself here.)

Before the transit begins, at 04:19 UT, Io and Ganymede will conjunct, as the picture below (first) shows us. Celestial Coordinates: [145.1" E; 20.6" S]. On the timing of the transit, Ganymede's shadow will ingress first at 14:06 UT (note before the actual dual-transit begins), and then Io's will at 14:22, signifying the start of the dual-transit. From there, Io will start its journey across Jupiter's luminous disk at 14:29 UT, and Ganymede at 14:34, starting the dual-transit of the moons.

Here, we can clarify the terms of dual-shadow transit, and dual-transit, becasue both can happen at the same time - the October 24 and 31 transits are great examples of these (among others). A dual-shadow transit occurs when two shadows of moons travel across the surface of Jupiter together (and yes this can also happen on any other planet with two or more moons, etc.), and then, when the two moons travel together, it is called a dual-transit. (The difference is just either the shadow or moon), but both have to cross Jupiter (or any other planet, etc.) at the same time.

You can see most of the events of this transit below, computer simulated, becasue 14:22 UT is 10:22 EDT; we here in America will not be able to view this transit (neither the 31). You can convert times here. {This is a rather sad fact for us here in America, but for those in East Asia, the Pacific, and some of the Middle East will enjoy seeing this treat. Jupiter here in America is high during night - and at Opposition, and it's very sad that we won't be able to see it!}


Monday, October 17, 2011

Dawn Provides Us With The First Official Information from Vesta

After the new "multimedia" was brought in in September, Dawn has yet brought back something else, and this time it's scientifical. Not to say that astronomical imagining is not scientific, Dawn has brought back information that proves scientifics, concerning the composition of Vesta, and topographical issues that have seen. At the annual meeting of the Geological Society of America in Minneapolis, Minnesota, astronomers brought forth their newly found evidence, here are some excerpts of what commenced and what comprised  the meeting:

"Dawn, which has been orbiting Vesta since mid-July, has found that the asteroid's southern hemisphere boasts one of the largest mountains in the solar system. Other findings show that Vesta's surface, viewed by Dawn at different wavelengths, has striking diversity in its composition, particularly around craters. Science findings also include an in-depth analysis of a set of equatorial troughs on Vesta and a closer look at the object's intriguing craters. The surface appears to be much rougher than most asteroids in the main asteroid belt..."

(The above quote was taken from JPL, a NASA affiliate, respectively). But astronomers do not know how these features on the surface of Vesta, formed. Yet, they presume some topographical information was caused by a massive impact, although not entirely sure yet.

The mission's principle investigator, Christopher Russell (University of California in Los Angeles), announced much at the meeting, including edits to previously held data. For example, "Russell said that the team has recalculated the rotational axis of the asteroid since Dawn’s arrival. Establishing a reliable coordinate system is essential for mapping Vesta’s many features, but the old coordinate system was 10° of," Sky&Telescope writes. Near the south pole of the planet, a giant basin lies now named "Rheasilvia," in tribute to the mother of Romulus and Remus This name is quite appropriate, for Vesta, in Roman mythology, is the goddess of the home, in that Rheasiliva was the leader of the Vestal virgins, those who worshiped that particular goddess. Sky&Telescope announces that "other features on Vesta will be named after related mythological characters," respectively.

Much of the southern hemisphere, including Rehasilva crater.

Other members of the team also did their share in discoveries. Carol Raymond (Jet Propulsion Laboratory), Dawn’s deputy principle investigator, has shown us a topographic map of Vesta, color-coded for different heights, near Rheasilvia. She's also helped us note the areas of different crater impacts, noting that "Vesta [has a] heavily cratered northern hemisphere and smoother areas in the south[ern hemisphere], the two halves separated by a set of grooves that gird the equator," Sky&Telescope writes. Hopefully, further study will help fill in unknown information. Andreas Nathues (Max Planck Institute, Germany) has shown us other color-coded topographical maps that notes craters and what they're comprised of. He suggests that, in the false-colored image, there "might be loosely packed material excavated during a low-angle impact," of a crater (from Sky&Telescope).

Shape model of southern hemisphere of Vesta showing complex structures, including the large south polar mountain, sinuous grooves, steep scarps and slumps.
Craters on Vesta shown in false color (left image) and clear filter (right image) of the FC. A color feature associated with the ejecta south of the main crater is one of the most prominent color features on Vesta’s surface


You can read much more at these links about Dawn & Vesta: