The June 5, 2012 Transit of Venus: Never Again Until 2117

Fred Espenak's composite image of the Transit of Venus 2004

After waiting since 2004 for another Transit of Venus, the 2012 Transit of Venus has finally arrived, preparing millions of viewers worldwide to see the spectacular event. Loosely described as the quiet silhouette passing across the luminous disk of the sun, the rare astronomical phenomena of the Transit has stunned and amazed astronomers throughout the ages and now another is upon us. You, who are reading this article now, will never be able to witness another Venus transit again in your lifetime: as the next comes in 2117. 

As we already know that Venus transits are rare, coming in couplets distributed over hundred year periods, what exactly is a transit, defined in an astronomical sense? Though eloquent as it may sound, planetary transits are far less common then eclipses, as the planets align much less frequently then the moon does. The Oxford Dictionary of Astronomy states that a transit is "the passage of one object across another of larger apparent diameter, such as Mercury and Venus in front of the Sun, or its shadow across the face of a planet." Correctively speaking, when a shadow crosses a larger object, it is hence called a shadow transit. So, there are two types of transits: shadow transits and regular transits (with no special name except for ‘transit’). Transits of planets across the Sun will not have a shadow cast, but usually transiting moons do. 

Io usually casts a shadow when transiting Jupiter’s surface (the Sun’s light help Io cast shadows), while Mercury won’t because it transit’s across the Sun’s disk—nothing is there to cast a shadow. That brings me to an important observation: only two planets may transit the Sun as viewed from earth. They are Mercury and Venus. Because earth is the third planet in planet progression in the solar system, we can only see two planets transit, whereas Saturn can see five; Mercury, Venus, earth, Mars, and Jupiter. Jupiter is probably big enough to blot out the Sun as viewed from Saturn, so it could be considered a planet eclipse. These are rare occurrences; and not much interest has been given to it. 

Yet, the history of such a rare astronomical phenomena is quite spectacular. Unlike eclipses that have been viewed from so early on in the books of the past, about one-thousand BC, the first transit (of any celestial body) was viewed on November 7, 1631 by French astronomer Pierre Gassendi. It was a transit of Mercury across the Sun’s disk; predicted by Johannes Kepler just four years before. Mercury also transited in years that followed; on November 7,1677 Sir Edmund Halley (who discovered Halley’s Comet) was the first man ever to witness a complete transit of Mercury, Gassendi obviously did not catch a whole transit, but a partial one. All that you really see is a black spot moving across the Sun’s surface. Mercury takes up 1/194 of the Sun’s disk, so although it may seem like nothing, it is an extremely rare astronomical event. 

Venus, because of having a larger orbit, transit much less frequently, making it an extremely rare event. Only seven events have ever been viewed since the making of the telescope (as of 2010). Just one month after Gassendi viewed the transit of Mercury, Venus transited, but when Gassendi tried to view it, he tried in vain, because the transit was not able to be seen in Europe. Later on, astronomers Jeremiah Horrocks and William Crabtree became the first two men ever to witness a transit of Venus, but there has been some controversy to that. On May 24, 1032 AD, Persian polymath Avicenna had claimed to be the first man ever to observe a transit of Venus. He wrote Compendium of the Almagest (a commentary on Ptolemy’s Almagest) in which he concluded that Venus is closer to Earth than the Sun. This was a great step in astronomy at the time, because geocentric views of the universe were taking shape. If the universe was geocentric, that meant the earth was the center of the universe. The heliocentric view (Sun is the center of the universe) was not used at all.

As mentioned before, only two planets may ever transit the Sun as viewed from earth. Mercury appears as a small speck on the Sun’s surface, while Venus is a bit larger. Edmund Halley, also used transits as a great help: “Edmund Halley first realized [in 1716] that transits could be used to measure the Sun's distance, thereby establishing the absolute scale of the solar system from Kepler's third law. Unfortunately, his method is somewhat impractical since contact timings of the required accuracy are difficult to make. Nevertheless, the 1761 and 1769 expeditions to observe the transits of Venus gave astronomers their first good value for the Sun's distance” stated the Transits Page at NASA’s eclipse website. This helped us determine how far the Sun is away from us, and gave Halley the credit for his observation. 

In 1631, 1639, 1761, 1769, 1876, 1882, and 2004 Venus was seen transiting. It is much rarer (Mercury transits so much more) because Venus’ orbit is much larger than Mercury’s. The larger the orbit of a planet is; the less likely an astronomical transit is to take place. Only in early June and December can you view one; if there is an eclipse in early June as well, then two spectacular events will occur in one week! On June 5/6 2012 (depending where you live on the globe) Venus will transit the Sun for the last time until 2117. On June 4^th (2012), a partial lunar eclipse will occur, so this week will be a treat for all who live around the Pacific Ocean. It turns out the complete visibility for the transit of Venus one/two days later is also the Pacific! (These may also be viewed In North America—but at sunset).

Transits of Venus are special—not only because they are so rare, but because they come in pairs of eight years. That explains why Venus transited in 2004 and will again in 2012. This is because the orbital periods of Venus (224.701 days) and earth are in an eight year (2922 days) resonance within each other. It takes eight years for earth to orbit around the Sun, and Venus thirteen, for both the orbits to exactly line up with each other. The first two times earth and Venus meet with each other, a transit is produced, but, Venus arrives twenty-two hours earlier the third meet, resulting in earth missing Venus completely. That’s why transits are so rare. The next one takes 105.5 or 121.5 years to make another transit. Two Mercury transits, on the other hand, are consecutive between 3.5, 7, 9.5, 10 or 13 years. This pattern is very complex on account of Mercury’s elliptical orbit. From there, a plethora of different year combinations come up, each resulting in a different calculation of years. By adding the years between transits, for example, one used commonly is 10 + 10 + 13 which equals 33, produces a better fit than just 10 or 33. Hundreds of combinations like these can be combined, giving us an irregular pattern of transits. 

Another boggling concept is transit ‘Saros.’ Just like the eclipse Saros, transits can be grouped into families. The Venus transits of the years 1518, 1761, and 2004 would belong to one family, while transits in 1639, 1882, and 2125 would belong to another. Those groups were determined by a period of 88,756 days (or 243 years) in which this transit ‘Saros’ is grouped. Mercury’s transits can also be grouped, as in one set (separated by 16,802 days or 46 years) separate the years 1957, 2003, and 2049 belong to one group, and 1960, 2006, and 2052 belong to another. Although a little too complex to explain in a short paper, transit ‘Saros’ is a very original idea; for almost all astronomical phenomena can be grouped in some way or another!

It is plain to see the history of transits is spectacular. But, will I be able to see the transit of Venus on June 5-6? The answer is yes and no. Yes: everyone on every continent at various times will be able to see the event. No: you need a special filter (to block out dangerous rays from the sun) and a telescope to see the actual planet. DO NOT LOOK DIRECTLY AT THE SUN, as its rays will blind you—many astronomy companies sell special filters for such events. 

Visibility map from eclipse-maps.com

For more on this amazing celestial events, Sky&Telescope has a plethora of information about viewing times and what you'll see with a telescope (and special filter!). 

SLOOH Space Telescope featuring Transit of Venus

See more images of the 2004 Transit of Venus Gallery thanks to Spaceweather.com

Simultaneous Planetary Transit: Mercury Transits Jupiter

Simultaneous astronomical planetary phenomena are rare spectacles only for those with pure, theoretical interest in astronomy becasue of the rarities and 'abstract' thought concerning it. Yes, we here on earth have and will experience transits of planets (only two, respectively Mercury and Venus), but Jupiter and the other planets have a better variety, with Neptune having the cadence of them all! Jupiter is able to see Mercury, Venus, Earth, and Mars transit the surface of the Sun, and it is an incredible finding that we were able to discern it!

On November 28, 2011, the planet Mercury will transit the face of the Sun, as seen only by Jupiter. But how can this be?, after all, we cannot even see it. Because the synodic period (orbital period) of each planet is 89.792 days, a formula can be calculated to determine such events, as shown below. P represents the sidereal orbital period of Mercury (which is respectively 87.968435 days) and Q represents the orbital period of Jupiter (respectively 4330.595 days). If we plug them into the equation we achieve these:

 

Now, of course, these simultaneous planetary transits are not very recent; below is the title of an article publish by the Royal Astronomical Society in 1886, Note on the Transit of the Planet Mars and its Satellites across the Sun’s disc, which will occur for the Planet Jupiter and its Satellites on April 13, 1886. It can be accessed here. Below is some general information about the transit, i.e., where will the planet pass and what coordinates will the sun be relative to Jupiter, etc.

Passage of Mercury across the Sun as seen from Jupiter

Transits of Mercury from Jupiter: 2005-2100
December 25, 2005	September 5, 2053
March 26, 2006	May 10, 2059
November 28, 2011	August 8, 2059
February 26, 2012	June 23, 2065
January 12, 2018	February 26, 2071
September 17, 2023	May 27, 2071
December 15, 2023	April 11, 2077
October 31, 2029	December 16, 2082
July 6, 2035	March 15, 2083
October 3, 2035	January 28, 2089
August 18, 2041	April 29, 2089
November 17, 2041	January 1, 2095
July 22, 2047	November 17, 2100
June 6, 2053

This is a rather central transit; as you see in the yellow Sun above with the path of Mercury, Mercury passes right through the center. February 26, 2011's transit (other link above) passes at the very top of the Sun. Therefore, this transit is rather rare.

Recent and Upcoming Transits

AD  2011 Nov 28  20:51 C     Transit of Mercury on Jupiter
    AD  2011 Dec 30  16:46 G     Transit of Mercury on Saturn 
    AD  2012 Feb 26  04:38 G     Transit of Mercury on Jupiter
    AD  2012 Mar 28  12:20 C     Transit of Mercury on Saturn 
    AD  2012 May 06  11:34 C     Transit of Venus on Saturn   
    AD  2012 Jun 06  01:31 C     Transit of Venus on Earth    
    AD  2012 Jun 25  08:10 C     Transit of Mercury on Saturn 
    AD  2012 Sep 20  09:54 C     Transit of Venus on Jupiter  
    AD  2012 Sep 22  04:16 C     Transit of Mercury on Saturn 

A Quintet of Saturnian Moons

Although not in transit, eclipse, occultation, or conjunction, these five Saturnian moons have perfectly fit into view of Cassini's camera, allowing us this picture. In the picture from left to right, the moon Janus (179 km across) is farthest left, then Pandora (81 km ac. - orbiting within the A & F ring in middle of image), Enceladus (504 km ac.) in center, Rhea (1,528 km ac. - Saturn's second largest moon), and Mimas (396 kn ac.) far right. NASA writes from the official publication of this picture:

This view looks toward the northern, sunlit side of the rings from just above the ringplane. Rhea is closest to Cassini here. The rings are beyond Rhea and Mimas. Enceladus is beyond the rings. The image was taken in visible green light with the Cassini spacecraft narrow-angle camera on July 29, 2011. The view was acquired at a distance of approximately 1.1 million kilometers (684,000 miles) from Rhea and 1.8 million kilometers (1.1 million miles) from Enceladus. 

Image Credit: NASA/JPL-Caltech/Space Science Institute

Yet, Jupiter's moons are much more acclaimed, Saturn is some competition. Jupiter has (approximately!) 64 confirmed moons. Saturn has 62 moons, although only 53 have been officially named. Astronomers are finding new moons every day, so these numbers will change, hopefully, as astronomers discovers new worlds of learning - after all, every moon is unique and is an individual!

Just for interest - here are the officially named Saturnian moons - funny how they look un-American: Aegaeon, Aegir, Albiorix, Anthe, Atlas, Bebhionn, Bergelmir, Bestla, Calypso, Daphnis, Dione, Enceladus, Epimetheus, Erriapus, Farbauti, Fenrir, Fornjot, Greip, Hati, Helene, Hyperion, Hyrrokkin, Iapetus, Ijiraq, Janus, Jarnsaxa, Kari, Kiviuq, Loge, Methone, Mimas, Mundilfari, Narvi, Paaliaq, Pallene, Pan, Pandora, Phoebe, Polydeuces, Prometheus, Rhea, Siarnaq, Skadi, Skoll, Surtur, Suttung, Tarqeq, Tarvos, Telesto, Tethys, Thrym, Titan and Ymir.

A Full Text of "Astronomical Events: Eclipses, Transits, Occultations & Conjunctions" is Finally Available to Read Online At Astronomical Events Calendar!

Written by Matthew Winter in the spring of 2011, this comprehensive essay discusses the nature and occurrences of eclipses, transits, occultations, and conjunctions. These rare phenomena have enchanted the mind of many -- especially unto the extent of mutual phenomena -- like an eclipse & transit occurring at the same time. Now, Astronomical Events Calendar has finally published this celestial masterpiece, and it can be obtained by clicking HERE!!

To define unknown terms:

Eclipse - a passing of a celestial body into the shadow of another, or casting one upon another. (From there, ou can distinguish solar & lunar eclipse. There are also exo-lunar eclipses, planetary eclipses, etc. All are defined in detail in the paper).

Transit - the passing of a body across another, such as the sun. (Do not confuse 'eclipse' with 'transit,' for a transit is a mini-eclipse. The reason why is in the paper.)

transit of venus, date ?

Occultation - the sudden disappearance of an object behind another. There are stellar occultations, planetary occultations, and lunar planetary occultations (find out more in the paper.)

Conjunction - the passing of two or more objects very close relative to each other as seen from earth. (Anything can conjunct. The moon and Saturn, Io (a Jovian moon) and Dione (a Saturnian moon) can conjunct as viewed from a certain location, etc.)

Extra-Planetary Eclipses and Transits

Our universe is a beautiful collection of celestial bodies revolving and rotating around the sun. Earth’s eclipses are best seen from earth, but who would think that other planets have eclipses as well? Every other planet in the solar system has natural satellites (except for Mercury and Venus—they grant us the favor of transits, though!) Why not their moons eclipse as well? Well, if our moon eclipses, then it’s true that other planet’s moons eclipse as well. Called extra-planetary eclipses, other planet’s moons eclipse wherein some planets with many moons do quite often. Take Mars for an example, March 5th 2004 was a historic day for NASA when they released the first pictures ever taken of an eclipse as seen from the surface of another planet. The pictures were taken by the Opportunity land-rover a day earlier. The pictures showed the moon Deimos passing like a tiny speck over the sun's disk. Actually, this is considered a transit, but it can also be referred to as an eclipse. Mars’ moons are way too small to create totality of darkness on the planet, unlike our moon (which was perfectly designed to eclipse perfectly!) The same goes for Jupiter and Saturn. They are so big that their tiny moons can only cast small shadows that look like specks of dust on the planet’s surface.

Phobos Transit as seen by Opportunity

But concentrating on Mars, Cornell University astronomer Jim Bell said “While Deimos would produce just a small speck traveling across the surface of the sun, we expect Phobos, because it's much closer to the surface (of Mars), to blot out half or more of the sun, it's a very quick event—it happens in 30 or 40 seconds or so.” It’s true that eclipses occur much more often on Mars than earth, but nothing compares to our moon eclipsing. Because Phobos, one of Mars’ moons, is only approximately twelve by fourteen miles in apparent size and orbits very swiftly, eclipses of Phobos would only last about thirty seconds because it takes it seven hours and thirty-nine minutes to orbit the planet. If the Martian day is twenty-four hours and thirty-seven minutes long, Phobos can eclipse twice daily! Annular eclipses are its only option because like annular eclipses of our moon, Phobos can never cover the entire Sun, but can fit inside it. Deimos, though, is considered not to eclipse, but to transit. Because it is five by six miles in apparent size, it is only viewed as a small object moving across the sun’s surface; this could be noted as an eclipse, but under more technical terms, it’s a transit.

 According to Jan Curtis, in his Predictable Astronomical Events, “Io (I), Europa (II), Ganymede (III), and Callisto (IV) act as a mini solar system. The moons’ commensurabilities with one another cause them to orbit with near perfect resonance. This means that these four giants cannot eclipse, occult, or be at greatest elongation with Jupiter all at the same time, although combinations of these phenomena occur.” Jupiter perhaps gives us a whole other solar system! With sixty-three moons and counting, Jupiter and its moons eclipse singularly (one moon at a time) non-stop—note that dual eclipses occur. Io, named from Ovid’s Metamorphoses—a fair virgin whom Jupiter (king of the Roman gods) fell in love with, even though he was already ‘married,’ has an orbital period of 1.769 days. This means every two days it will transit across the surface of Jupiter. Often eclipsing, Io is very ‘busy’ because it spends 10.8% of its orbital period transiting, eclipsing, and occulting daily! Europa, also named (as well as the rest of the Galilean moons) from Ovid’s Metamorphoses, who Jupiter falls in love with, has an orbital period of 3.551 days and spends 6.75% of its orbital period transiting, etc. Then Ganymede, with an orbital period of 7.155 days and spending 4.2% of its orbit ‘busy,’ and Callisto, having an orbital period of 16.689 days and spending only 2.5% ‘busy’ both transit, etc. but, not as often because their orbits are more elongated, then those of Io and Europa.

Eclipses of the Galilean moons are perhaps the most spectacular. Although you can view Jupiter clearly with the naked eye, but viewing the Galilean moons requires more equipment, such as a small telescope or even a good pair of binoculars. “...Strung along Jupiter’s waistline,” The Rough Guide to the Universe describes these moons so vividly. But, how do these moons play their role in the universe? Discovered between 1610 and 1612, Galileo first observed four moons of Jupiter. After observing them for a while, he was soon able to create tables and predictions of the movements of these satellites that were actually correct. But later in the 1600s, Giovanni Domenico Cassini (the satellite ‘Cassini’ that went to explore Saturn in 1997 was named after him), also contributed works on Jupiter’s moons. Using his charts, he determined Io’s correct longitude; and as measured today, he was just off one degree. So, these four moons (Io, Europa, Ganymede, and Callisto) have an incredible history, let alone they have been orbiting throughout the ages.

More on eclipses, what actually is a Jovian eclipse? Although much different than an eclipse of our moon, Calsky (a website that calculates astronomical events) defines a Jovian eclipse as this: ‘if a moon enters the shadow cone of Jupiter, it gets eclipsed and disappears pretty fast.’ So, whenever a Jovian moon (or a Galilean subset—Galilean moons are a subset of Jovian moons; Jovian moons include all moons of Jupiter—all sixty-three) enters Jupiter’s shadow cone, it will be eclipsed. Eclipses can be partial, in where only a portion of the moon is eclipses, or total, where the whole moon is eclipsed. One such example of series (yes, Jovian eclipses follow their own ‘Saros’ too!) of Jovian eclipses occurred in 1999. Jupiter and Saturn returned to the sky in autumn of that year; Jupiter was at its best to view in a long time. Jupiter and its moons were easily observed with a small telescope, and two of three phenomena could easily be seen. Transits and occultations were easy to see, but not so much eclipses. That’s what makes eclipses so amazing. Capitol Skies (the newsletter of the Madison Astronomical Society) tells us this about Jovian eclipses: “Jupiter provides a virtual smorgasbord of events to watch. Of the three events, eclipses are by far the most scientifically interesting, because the timing of the precise disappearances and reappearances of the moons can be used to calculate orbital elements of the moons. For this reason, precise timings of the Galilean moon eclipses are sought by the Association of Lunar and Planetary Observers (ALPO).”

Just like eclipses here on earth, precise timings are everything; not as much location. If you can see Jupiter, then you can see an eclipse. Because its shadow cast is very magnificent, when a Galilean moon passes behind it, it disappears completely from view, but has not been occulted. As well as that, because the shadow cast is so steep, the Galilean moons may be viewed entering and exiting the shadow on the same side of the planet! But the closer Jupiter is to opposition (when Jupiter is opposite from the Sun in the sky), the closer these eclipses happen to the disk of Jupiter, making them harder to view. Depending on Jupiter’s position relative to the earth and to the Sun, the eclipses may be viewed easily and is best viewed when Jupiter is near quadrature. Quadrature is simply being ninety degrees west or east from the Sun; away from ‘hard-to-see’ opposition.

Saturn, Uranus, and Neptune have moons that eclipse as well, but aren’t widely as known as Jovian eclipses. Pluto, on the other hand, has three moons that eclipse. It’s rare for a dwarf planet to have moons, but Pluto does; as also does Eris. Eris is a dwarf planet far beyond Pluto (ninth largest body to orbit the Sun), and has one moon: Dysnomia, which orbits every 15.8 days.  Nothing is clearly known whether its moon eclipses, because it’s just too far away to detect. More than likely, it does, along with other events! But, Pluto and its three moons (Charon, Nix, and Hydra) have another story to tell. February 1985 and October 1990 were the years in which Pluto experienced solar eclipses that lasted for hours; but on average ninety minutes. In order to view this event, you had to be on Pluto, and I doubt anyone was there.

Basically, solar eclipses on Pluto are caused by Charon (which is big enough to make Pluto experience totality—Charon is more than one-half the size of the dwarf planet!), passing in front of the Sun, blocking its light. Of course Hydra and Nix can eclipse as well, but they are much smaller, so Pluto would not experience totality on its surface; it’s more of a transit. But, Nix and Hydra did not eclipse then, because they weren’t even discovered until 2005! An eclipse of this sort can only occur when one of the satellites’ orbital nodes are lined up with the apparent position of the Sun, as seen from Pluto. Because of the fact that all three of its satellites orbit in the same plane, the times at which this is possible are the same for all three. Pluto has a steep axial tilt, so eclipses can only occur around the dwarf planet’s perihelion and aphelion (the closest and farthest point of a planet’s orbit).

It’s easy for Charon to eclipse, but not Hydra and Nix. We know that they are smaller than Charon, but we don’t know how big the really are. That’s when eclipses helped. During that period between 1985 to 1990, the solar eclipses that Charon and Pluto’s other moons made, helped determine their actual sizes. That was a great step in research about Pluto, because no man-made satellite has ever been there before. NASA sent out New Horizon’s mission which is expected to reach and explore Pluto in 2015. That will definitely be a great accomplishment! Eclipses were able to be viewed every day, and while Pluto experienced a solar eclipse, earth was able to view a transit of Charon across Pluto’s surface. During the start of this five year period, the eclipses began blocking the North Polar Region of the dwarf planet, but as the year progressed, the equator was blocked. By means of carefully measuring the brightness over time, it was possible to determine surface features. Pluto has a highly reflective south polar cap, a dimmer north cap, and dark features around its equator. All these were discovered by the help of a solar eclipse—a great step in research!

When the eclipses began, in order to measure the diameters of the moons, apparent diameters cast on the dwarf planet were taken, and the Hubble Space Telescope helped by taking pictures and sending them back to earth for studying purposes. Hubble’s images showed that Pluto’s diameter is 1413 miles wide; Charon’s is 728 miles wide. Although Nix and Hydra weren’t measured, we now have the correct diameters of these bodies in which we knew nothing about previously! The next eclipses will occur in October 2103, so none of this generation will be able to view them. They peak in 2110, and finish in January of 2117. Much more will be learned about this distant planet during those eclipses as well. Maybe Nix and Hydra will choose to eclipse next time.

As magnificent as transits of Mercury and Venus are, there are those that are more magnificent. How would you like to observe earth transit? Think about this for a minute, other planets can transit the Sun; but, we can’t see them. We can’t see Uranus transit, but it does as viewed from Neptune. Therefore, Neptune can transit as not viewed from Uranus, but from Pluto. Ranging from mutual planetary transits, solar-system planetary transits, simultaneous transits, extra-lunar transits, and so forth, much more occurs than what the average person knows. Mars might be transiting the face of Neptune as viewed from Mercury right now for all I know! A planet, the Sun, and another planet are all that it takes to create a special transit.

But before we discover true rarities, exo-lunar transits must be made known first. An extra-lunar transit simply put us a transit of another planet’s (other than earths) moon across the surface of it. As mentioned countless times already, the Jovian moons put on quite a show daily. One moon will either eclipse, occult, transit, or do two or all three in a single day. Io does frequently transit, as well as Europa, Ganymede, and Callisto. So does Saturn’s moons. On February 24th 2009, something happened so rare; it will probably never repeat itself again. “On Feb. 24th, there's going to be a quadruple transit of Saturn's moons,” says Keith Noll of the Hubble Space Telescope Science Institute. “Titan, Mimas, Dione and Enceladus will pass directly in front of Saturn and we'll see their silhouettes crossing Saturn's cloud tops—all four at the same time.” Sure enough, all four moons cast shadows as they transited as well. At the end of that magnificent event, each moon and shadow had been on the surface of Saturn, a true gem! Another event happened on Jupiter, but earlier. March 28th 2004 hosted a triple-transit of Io, Ganymede and Callisto all traveling across Jupiter’s disk. They also cast beautiful shadows that made this event rare as well. Something even more peculiar occurred to Saturn. Dione transited Titan, as seen by the Cassini probe; and in the background, Prometheus became occulted by the rings of Saturn. It’s not that common moon will transit another moon (exception—Saturn’s Enceladus transited Titan on February 5th 2006) and rings occult another. Not much like that happens every day!

Jovian dual transits are another wondrous thing. Although occurring in periods just about twice a year, two Jovian moons will line up with each other and transit the surface. Although three have occurred in 2011 already, the next ‘season’ starts May 7th 2011. Io will either transit with Europa or Ganymede; but more frequently Europa. Dual shadow transits, dual-transits just with both the moon’s shadows on Jupiter’s disk, instead of one, start on May 14th 2011 and run until June 26th 2011, while dual-transits end on June 15th. This will be a great time to photograph and record information.

Rare triple-transit on Jupiter

[This is a special interest story, written by Matthew Winter from his research paper entitled Astronomical Events: Eclipses, Transits, Occultations, and Conjunctions.]