domingo, 3 de junho de 2012

Partial Lunar Eclipse of June 04

Partial Lunar Eclipse of June 04

The first lunar eclipse of 2012 occurs at the Moon's ascending node in southern Ophiuchus about 6° northeast of Antares (mv = +1.07). It is best seen from locations in and near the Pacific Ocean (Figure 3). Most of the Americas will experience moonset before the eclipse ends while eastern Asia will miss the beginning of the eclipse because it occurs before moonrise. The Moon's contact times with Earth's shadows are listed below.
                 Penumbral Eclipse Begins:    08:48:09 UT
                 Partial Eclipse Begins:      09:59:53 UT
                 Greatest Eclipse:            11:03:13 UT
                 Partial Eclipse Ends:        12:06:30 UT
                 Penumbral Eclipse Ends:      13:18:17 UT

At the instant of greatest eclipse the umbral eclipse magnitude will reach 0.3705. At that time the Moon will be at the zenith for observers in the South Pacific. In spite of the fact that just a third of the Moon enters the umbral shadow (the Moon's southern limb dips 12.3 arc-minutes into the umbra), the partial phase still lasts over 2 hours. 

Figure 3 shows the path of the Moon through the penumbra and umbra as well as a map of Earth showing the regions of eclipse visibility. New England and eastern Canada will miss the entire eclipse since the event begins after moonset from those regions. Observers in western Canada and the USA will have the best views with moonset occurring sometime after mid-eclipse. To catch the entire event, one must be located in the Pacific or eastern Australia. 

The table below gives times of each phase of the eclipse for various time zones in North America and Hawaii. 

Partial Lunar Eclipse of 2012 June 04
EuropeNorth AmericaPacific
Penumbral Eclipse Begins: 08:48 am 04:48 am 03:48 am 02:48 am 01:48 am 12:48 am 10:48 pm
Partial Eclipse Begins: 10:00 am 06:00 am 05:00 am 04:00 am 03:00 am 02:00 am 12:00 am
Greatest Eclipse: 11:03 am 07:03 am 06:03 am 05:03 am 04:03 am 03:03 am 01:03 am
Partial Eclipse Ends: 12:06 pm 08:06 am 07:06 am 06:06 am 05:06 am 04:06 am 02:06 am
Penumbral Eclipse Ends: 01:18 pm 09:18 am 08:18 am 07:18 am 06:18 am 05:18 am 03:18 am
                    Time Zone Abbreviations

                    GMT  - Greenwich Mean Time
                    EDT  - Eastern Daylight Time (GMT - 4 hours)
                    CDT  - Central Daylight Time (GMT - 5 hours)
                    MDT  - Mountain Daylight Time (GMT - 6 hours)
                    PDT  - Pacific Daylight Time (GMT - 7 hours)
                    AKDT - Alaska Daylight Time (GMT - 8 hours)
                    HST  - Hawaii Standard Time (GMT - 10 hours)
The June 04 partial lunar eclipse belongs to Saros 140, a series of 77 eclipses in the following sequence: 20 penumbral, 8 partial, 28 total, 7 partial, and 14 penumbral lunar eclipses (Espenak and Meeus, 2009). Complete details for the series can be found at: 

The 2012 Transit of Venus

On June 5th, 2012, Venus will pass across the face of the sun, producing a silhouette that no one alive today will likely see again.

Transits of Venus are very rare, coming in pairs separated by more than a hundred years. This June's transit, the bookend of a 2004-2012 pair, won't be repeated until the year 2117. Fortunately, the event is widely visible. Observers on seven continents, even a sliver of Antarctica, will be in position to see it.

The nearly 7-hour transit begins at 3:09 pm Pacific Daylight Time (22:09 UT) on June 5th. The timing favors observers in the mid-Pacific where the sun is high overhead during the crossing. In the USA, the transit will be at its best around sunset. That's good, too. Creative photographers will have a field day imaging the swollen red sun "punctured" by the circular disk of Venus.

Observing tip: Do not stare at the sun. Venus covers too little of the solar disk to block the blinding glare. Instead, use some type of projection technique or a solar filter. A #14 welder's glass is a good choice. Many astronomy clubs will have solar telescopes set up to observe the event; contact your local club for details.

Transits of Venus first gained worldwide attention in the 18th century. In those days, the size of the solar system was one of the biggest mysteries of science. The relative spacing of planets was known, but not their absolute distances. How many miles would you have to travel to reach another world? The answer was as mysterious then as the nature of dark energy is now.

Venus was the key, according to astronomer Edmund Halley. He realized that by observing transits from widely-spaced locations on Earth it should be possible to triangulate the distance to Venus using the principles of parallax.

The idea galvanized scientists who set off on expeditions around the world to view a pair of transits in the 1760s. The great explorer James Cook himself was dispatched to observe one from Tahiti, a place as alien to 18th-century Europeans as the Moon or Mars might seem to us now. Some historians have called the international effort the "the Apollo program of the 18th century."

Photo from the 2004 Venus Transit showing Venus and the International Space Station crossing the sun.
A double transit: the International Space Station and Venus on June 8, 2004. Photo courtesy of Tomas Maruska. 

  In retrospect, the experiment falls into the category of things that sound better than they actually are. Bad weather, primitive optics, and the natural "fuzziness" of Venus’s atmosphere and other factors prevented those early observers from gathering the data they needed. Proper timing of a transit would have to wait for the invention of photography in the century after Cook’s voyage. In the late 1800s, astronomers armed with cameras finally measured the size of the Solar System as Edmund Halley had suggested.

This year’s transit is the second of an 8-year pair. Anticipation was high in June 2004 as Venus approached the sun. No one alive at the time had seen a Transit of Venus with their own eyes, and the hand-drawn sketches and grainy photos of previous centuries scarcely prepared them for what was about to happen. Modern solar telescopes captured unprecedented view of Venus’s atmosphere backlit by solar fire. They saw Venus transiting the sun’s ghostly corona, and gliding past magnetic filaments big enough to swallow the planet whole.

2012 should be even better as cameras and solar telescopes have improved. Moreover, NASA’s Solar Dynamics Observatory is going to be watching too. SDO will produce Hubble-quality images of this rare event.

World map show visibility of transit of Venus on June 5-6, 2012. › View larger
World visibility map for June 5-6, 2012 Venus Transit. Credit: M. Zeiler

Sol sobreviverá à colisão da Via Láctea com Andrômeda

Simulação mostra como parecerá o céu noturno na Terra logo no início da fusão da Via Láctea com a galáxia de Andrômeda, daqui a 4 bilhões de anos Nasa
RIO – Astrônomos da Nasa usaram dados do telescópio espacial Hubble para simular um dos eventos mais extremos que nossa vizinhança cósmica vai passar, o choque da Via Láctea com a galáxia de Andrômeda (M31), prevista para acontecer daqui a 4 bilhões de anos. De acordo com os modelos, o Sistema Solar, e a Terra, deverão sobreviver à colisão, mas provavelmente serão lançados a uma nova região do espaço.
- Nossos achados são estatisticamente consistentes com uma colisão de frente entre Andrômeda e nossa Via Láctea – disse Roeland van der Marel, do Space Telescope Science Institute (STScI), que administra o Hubble.

A simulação foi possível após detalhada análise de dados do telescópio espacial sobre o movimento de Andrômeda. A galáxia hoje está a cerca de 2,5 milhões de anos-luz de distância, mas avança velozmente em direção da Via Láctea devido à atração gravitacional mútua. O modelo ostra ainda que serão necessários outros 2 bilhões de anos para que as duas galáxias se unam completamente, deixando para trás seus formatos espirais e transformando-se em uma imensa galáxia elíptica.

- Depois de quase um século de especulação sobre o futuro destino de Andrômeda e da Via Láctea, finalmente temos um cenário claro de como os eventos vai se desdobrar nos próximos bilhões de anos – contou Sangmo Tony Sohn, também do STScI.

Embora as galáxias entrem em choque, as estrelas dentro delas estão tão afastadas uma das outras que elas não deverão colidir no encontro. Apesar disso, elas serão lançadas em novas órbitas em torno do novo núcleo galáctico e as simulações indicam que nosso Sistema Solar provavelmente será lançado para mais longe dele do que atualmente está. Para deixar tudo ainda mais complicado, no entanto, a galáxia do Triângulo (M33), anã companheira de Andrômeda, vai se juntar à colisão e provavelmente se fundir ao par Andrômeda-Via Láctea. Há ainda uma pequena chance da M33 se chocar com a Via Láctea antes de Andrômeda.


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