Stefan Réner, Ahmed Daassou and Zouhair Benkhaldoun took this image of Pluto and
the target star, using the T60cm from Atlas Golf Marrakesh on the night 12 to 13
June. Credit
Although the suddenness of such an event is rather peculiar (as such an event should have been in ephemerides without such short notice), Pluto perhaps will occult the a star, P20120614 of the 13.7 magnitude during the night of June 13-14. In an alert entitled "Possible Pluto occultation Wednesday night (2012/06/14 03:28 UT) from US East coast" issued by Leslie Young, we find that Pluto's occultation hopefully will conclude to be helpful for more insight to Pluto, as it is a world of which we do not have much information from. The occultation is planned to last around sixty-eight seconds starting on June 14 at 3:22 UT (June 13 11:22 pm EDT) at a low altitude in the sky for the eastern United States and Canada. The RA (Right Ascension) of the star is 18h 35m 48.69s while declination is at –19° 17' '43.6".
From the alert, we learn that stellar occultations prove to help us learn more about Pluto, but particularly its atmosphere. "Pluto's thin, nitrogen atmosphere is in vapor-pressure equilibrium with the surface ice, and changes seasonally", so observable occultations will help astronomers learn more about the atmosphere. When Pluto passes in front of a star, we get a good view of the atmosphere by the light from the star behind the planet and meanwhile, at ~10 km resolution, temperature and pressure is measured accordingly. More information can be obtained here.
Visibility Map: Across the globe pictured above, the three solid lines correspond to the
northern limit, centerline, and southern limit of Pluto's shadow. The northern
and southern limits correspond to a radius of 1400 km. The upper and lower
dashed lines indicate 3-sigma errors. The shaded area represents where the sun
is more than 12 degrees below the horizon.
Position Angle (Pluto relative to the
star; measured north through east)
–6.40 degrees
Geocentric Velocity
22.89 km/sec
Occultation Star R magnitude
13.8
Table 2: Reference Star Position
Reference star position:
(at epoch of event)
RA (h:m:s; J2000)
Dec (d:m:s; J2000)
Notes
P20120614 Catalog
18 35 48.6931
–19 17 43.617
P20120614 Measured
18 35 48.6883 ± 0.002
–19 17 43.639 ± 0.009
From
5 SMARTS Telescope frames.
Table 3: Projected KBO Offsets from Reference Ephemeris at the Time
of the Event
Body
RA (arcsec)
Dec (arcsec)
Pluto
–0.1392± 0.041
+0.225± 0.023
Above Tables and Visibility Map Thanks toP20120614 Occultation June 14, 2012. Below map credit same site the image of Pluto and Star (beneath the title) was accessed.
Dark gray is night and light gray is astronomical twilight (Sun
at less than 18° below the horizon). Shadow moves from right to left, each red dot is
separated by one minute, the nominal occultation time on the map, is for the big
red dot, the closest approach
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 4th (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!).
Being the second major solar eclipse event of 2012, the annular eclipse of May 20, 2012 is sure to bring about some impressive photographs as the moon passes in front of the sun. Unlike typical solar eclipses, annulars constitute a niche in astronomical classification for eclipse not only because of their rarity, but mostly because of their peculiarity. An eclipse, loosely defined, occurs when the moon passes in front of the sun, leaving a certain place on earth with no or some part of the sun, as seen by inhabitants of a region. The moon literally blocks out part of the sun for observers. However, depending whether the moon is at apogee and perigee can help define whether such an event will be annular or not. As defined in Matthew Winter's Astronomical Events: Eclipses, Transits, Occultations and Conjunctions, we get a good picture on the elements of an annular eclipse.
It [an annular solar eclipse] is defined as ‘a solar eclipse
in which the Moon's antumbral shadow traverses Earth (the Moon is too far from
Earth to completely cover the Sun). During the maximum phase of an annular
eclipse, the Sun appears as a blindingly bright ring surrounding the Moon,’
from NASA’s Glossary of Solar Eclipse
Terms. Annular eclipses are straightforward as well; the moon is fully
inside the Sun’s disk, but does not cover it. This is because the moon is at
perigee. The closer the earth to the moon, the more frequent the annular
eclipse. The sun appears as a great ring, because the moon’s orbit is not
completely circular, rather it’s an ellipse that travels in an oval.
Unfortunately, the Sun’s corona is lost, but a few phenomena occur; annular eclipses only produce shadow bands, but are usually
hard to see, even if any occur. It cannot produce Baily’s beads or the
diamond-ring affect, because those can only happen under complete totality. So,
on occasions, shadow bands will come into view, but don’t count on it. They’re
blurry and difficult to relate to if you see any.
In short, annular eclipses have only one important criterion that must be met in order to form such an event: the moon must be at perigee, or farthest from the sun; only then can the sun be seen as a complete ring, which was named accordingly. (Annulus is the Latin word for "ring").
Visibility for the May 20, 2012 eclipse
Statistics for this eclipse, the visibility and frequency of others of its kind, are great. Visibility entails where the event will be able to be seen: from Eastern China across the Pacific Ocean to the Southwestern States are among the multitude of places that spectators will be able to witness the eclipse. "In the United States, the eclipse begins at 5:30 pm PDT and lasts for two hours. Around 6:30 pm PDT, the afternoon sun will become a luminous ring in places such as Medford, Oregon; Chico, California; Reno, Nevada; St. George, Utah; Albuquerque, New Mexico, and Lubbock, Texas. Outside the narrow center line, the eclipse will be partial. Observers almost everywhere west of the Mississippi will see a crescent-shaped sun as the Moon passes by off-center," Spaceweather.com comments. The point of greatest visibility will take place just south of the Aleutian Islands in the North Pacific for five minutes and forty-six seconds. This will be the place where the ring, or annulus, will be seen the greatest.
Taking part in Saros Cycle 128, the annular eclipse of May 20 2012 repeats every eighteen years and eleven days, altogether containing 73 events. "Solar eclipses of Saros 128
all occur at the Moon’s descending node and the Moon moves northward with each eclipse.
The series began with a partial eclipse in the southern hemisphere on 0984 Aug 29.
The series will end with a partial eclipse in the northern hemisphere on 2282 Nov 01.
The total duration of Saros series 128 is 1298.17 years," NASA's eclipse website propagates. For more about Saros 128, NASA's eclipse website's database is superb. More information about Saros can be found there as well.
When viewing this annular eclipse, like any other solar eclipse, it is important that one realizes the safety precautions that need to be made known. Do NOT attempt to look at the sunwithout the appropriate filter (or even sunglasses), because of the high risk for blindness. Many astronomical websites have stores where you can buy the appropriate equipment for viewing the sun.
