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The July Occultation Of Jupiter By The Moon: July 15th ~12:30 UTC – July 15th 02:50 UTC

In the early hours of Sunday, July 15th, the Moon will pass in front of Jupiter and four of its moons. Luckily, and provided the cloud stays well away, Cornwall will be an area which will essentially witness a full-to-partial occultation (although I am very excited to see grazing occultation photos from the astronomical community), so I will be partaking in some lunar viewing with the hope of drawing what I see. If you are viewing in the U.K., the southeast and eastern parts of the south coast are on the edge of the occultation. The further north and west you go, the further the separation between the Moon and Jupiter.

Nonetheless, the view should be stunning where ever  you may be in England, and this occultation may give you your first naked eye view of Jupiter as it is extremely easy to spot. The crescent Moon, as seen around 01:54 UTC (02:54 BST) on the morning of the 15th of July, should occult Jupiter and four moons: with the set being (from left to right as seen from the northern hemisphere) Callisto, Ganymede, then Jupiter itself as the largest -1.9 magnitude source, followed by Io and Europa being occulted first. The predicted mid-occultation time will be approximately 02:05 UTC (03:05 BST).

The June 2012 Transit Of Venus: June 5th 22:09 UTC – June 6th 04:49 UTC

The transit of Venus is perhaps one of the most amazing and one of the rarest events we are likely to witness. It is the last one this century: the next being in 2117! (Venusian transits are among the rarest of predictable celestial phenomena and occur in pairs eight years apart*: the previous transit having been in June 2004, the next pair of transits will not occur until December 2117 and December 2125.) For this reason, the transit is truly the most amazing astronomical event of 2012. The transit will begin at 22:09UTC on 5 June 2012, and will finish at 04:49 UTC on 6 June. Depending on the position of the observer, the exact times can vary by up to ±7 minutes. So what is so amazing about a dark black dot crossing the solar disc early on Wednesday morning?

N.B.* This is only a general guide rather than a rule, some transits occur once every 105 years, e.g. 1153 A.D and 1396 A.D were singular transits. Of course, in years to come this will change.

One reason is the historical significance to the astronomical community. The first recorded transit, way back in 1639, was by Jeremiah Horrocks. Such early observations allowed Horrocks and his contemporaries to estimate the size of, as well as the distance to, Venus. However, rather remarkably Horrocks has also able to make an estimated measurement of the distance between the Sun and the Earth: a unit now known as the astronomical unit, the “A.U” (1A.U). The A.U is now one of them most fundamental yardstick for studies of our solar system and our local region of the Milky Way galaxy, serving as an excellent comparative measurement to quantify the sheer distance of many a planetary nebula and supernova remnant. By the 18th century it was realised that the best measure of an astronomical unit could be made by watching the transit of Venus from different places on the earth and then using trigonometry to calculate the distance. Exploiting such “parallax” measurements became an international cause of the age of enlightenment: as for the 1769 predicted transit astronomers from Great Britain were dispatched to all corners of the Empire to view the event from both hemispheres and from different latitudes as possible. Also, if you have ever travelled to Tahiti you may notice a place called “point Venus”. This is where Captain Cook and a team of astronomers were dispatched to record the impending transit.

Exploiting the parallax method was first proposed by the enigmatic Edmond Halley (for which, Halley’s comet is named after). In 1716 astronomer Halley calculated that you can quantify the distance from the sun to the earth by having observers across the globe time the passage of Venus across the sun.  Knowing he would not live to see the next transit, Halley predicted global sites that would be suitable for viewing a transit and called upon future generations to pursue his plan.  As mentioned in the pervious paragraph, the distribution of astronomers to all corners of the globe was the best way to accurately quantify the distance to the Sun. Without Halley’s predictions and mathematical genius, the 1761 transit and every transit opportunity since then, explorers would not have sailed to distant lands to time the transit.  The quest to time the transit of Venus in 1761, during the Seven Years War, marked one of the first times the international community cooperated to answer one of the leading scientific questions of the day. Although the AU has now been well designated by modern astronomical methods, a global effort to measure the distance to the Sun for the digital twitter-inspired age can be found at: [transit2012.org], where anyone can take part.

The safest way to watch a transit is to observe an image of the Sun projected onto a screen through a telescope, binoculars, pinhole or reflected pinhole The event can be viewed without magnification using filters specifically designed for this purpose, such as an astronomical solar filter or eclipse viewing glasses coated with a vacuum-deposited layer of chromium. However, the disk of Venus is tiny compared to the sun and not much will be seen. The once-recommended method of using exposed black-and-white film as a filter is not now considered safe, as small imperfections or gaps in the film may permit harmful UV rays to pass through. Observing the Sun directly without appropriate protection can damage or destroy retinal cells, causing temporary or permanent blindness. So please do not view the Sun directly!

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