Last Story Transit of Venus Cover in the 21st Century K. SMILES MASCARENHAS Planet Venus is fast approaching the Sun for a rendezvous on the 6th of June 2012. If you miss it, you will have to wait till the year 2117! “We are now on the eve of the second HESE prophetic words were written by When two heavenly bodies apparently transit of a pair, after which there will be William Harkness, an astronomer who cross each other’s path as seen from the no other till the twenty-first century of our Tled the American efforts for the 1882 Earth, we have the following three era has dawned upon the Earth, and the transit of Venus, and the one who almost possibilities: June flowers are blooming in 2004. When single-handedly achieved the final 1. Eclipse: When two heavenly objects the last transit season occurred the American result. It is remarkable that having apparently the same size (that is, intellectual world was awakening from Harkness was trained in medicine, and they appear to be roughly the same size the slumber of ages, and that wondrous served as a surgeon in the Union Armies as observed from the Earth) cross each scientific activity which has led to our during part of the American civil wars, other’s path, we say an eclipse takes present advanced knowledge was just before he became a full-fledged place. For example, during the eclipse of beginning. What will be the state of astronomer! the Sun, even though the Moon is much science when the next transit season Yet another Venus transit is fast smaller, it appears to be of the same size arrives God only knows. Not even our approaching – on 6 June 2012 to be as the Sun, because it is nearer to us. children’s children will live to take part in precise. If you miss this event, you may Therefore, it can completely hide the Sun the astronomy of that day. As for perhaps not be alive to witness it when it behind it. th ourselves, we have to do with the occurs next on the 11 of December 2117. 2. Occultation: When an apparently larger present . .” But before we proceed further, let us try to heavenly object covers an apparently get an idea about what a transit actually smaller one, we say an occultation occurs. is. For example, when the Moon blocks the SCIENCE REPORTER, MAY 2012 8 Cover Story Black drop effect Penumbra Umbra Moon Earth SUN Anatomy of transits of Venus occur in pairs separated Transits of Venus occur in pairs an eclipse by eight years. But these pairs are very because the length of eight Earth years is rare! They occur once every 113.5 years almost the same as 13 years on Venus, so or 129.5 years (on the average roughly every eight years the planets are in roughly every 121.5 years). It is remarkable that the same relative positions. This the pairs occur alternately in the month approximate conjunction usually results in light coming from a star, we say that the of June and December! a pair of transits, but it is not precise Moon has occulted the star. We are now on the eve of the second enough to produce a triplet, since Venus 3. Transit: When an apparently smaller transit of the pair in the twenty first century. arrives 22 hours earlier each time. The last object traverses in front of an apparently The last transit of Venus occurred on 8th of transit not to be part of a pair was in 1396 larger one, we say a transit occurs. For June 2004 and the next is predicted to A.D., the next will be in 3089. example, it is known that the inferior planets happen on the 6th of June 2012. Transits of Venus had great importance Mercury and Venus (inferior, because their If the orbit of Venus were not inclined during the early history of modern orbits lie within the orbit of the Earth; all the to ours, a transit would occur every time astronomy. In fact, it was the only time when other planets are called superior planets Venus moves in between the Sun and the astronomers had a chance to determine because the radii of their orbits are greater Earth, that is, at inferior conjunction. The the value of the Astronomical Unit (or AU than that of the Earth) can occasionally orbit of Venus, however, is inclined at an as it is called, the average distance cross the Sun’s disc when viewed from the angle of 3.4 degrees to the ecliptic (the between the Sun and the Earth). During Earth. plane of Earth’s orbit), which causes Venus modern times, the AU can be estimated There can be many transits of Mercury to usually pass above or below the Sun at to a greater accuracy using space probes during the century. But the transits of Venus inferior conjunction as seen from the Earth. and radar techniques. So the transit of across the disc of the Sun are among the Only when both Venus and Earth are Venus arouses interest not because of its rarest of planetary alignments. Indeed, approximately at the line of the nodes, importance to astronomy, but because it only six such events have occurred since along which the orbital planes of Venus is so rare! the invention of the telescope (1631, and the Earth cross, there is a possibility for The next Venus transit pair after the 1639, 1761, 1769, 1874 and 1882). The a transit to take place. 2012 event will occur on 11th of December 9 SCIENCE REPORTER, MAY 2012 Cover Story 2117 and on 8th of December 2125 (before for Mars or Saturn; but otherwise very calendar were to be followed, the date 1526 A.D, Venus transits occurred on May accurate. Like another astronomer, Omar would be 4th of December 1639). and before 1396 A.D, they occurred in Khayyam, Horrocks was also a poet, and As it always happens, it turned out to November; till the 44th century, transits of he wrote his poetic verses in praise of his be a cloudy day. Although he was Venus will occur only in June or telescopes and the heavenly objects! uncertain of the exact time, Horrocks December!). In 1627, Johann Kepler (1571-1630), calculated that the transit was to begin at The time of occurrence of the 21st using his laws of planetary motion approximately 3:00 pm. Horrocks focused century Venus transits shows that the 2004 prepared the Rudolphine tables, consisting the image of the Sun through a simple transit was placed comfortably for viewing of a star catalogue and a table of telescope onto a piece of card, where from India, from the start to the finish. Many planetary positions. Based on it, he the image could be safely observed. After amateur astronomers in India observed it predicted the December 1631 transit of observing for most of the day, he was lucky by simply projecting the Sun’s image on Venus, but wrongly predicted that in 1639 to see the transit as clouds obscuring the the walls of their room. Only the closing Venus would narrowly miss transiting the Sun. Sun cleared at about 3:15 pm, just half an stages of the 2012 transit will be visible from Kepler never lived to see his 1631 hour before sunset. India. Still, there will be live coverage of prediction come true, having missed it by Horrocks is remembered on a plaque this rare event by many TV channels. just one year! in Westminster Abbey and the lunar crater Horrocks corrected Kepler’s Horrocks is named after him. In 1859 a History of Observations calculation for the orbit of Venus and marble tablet and stained glass window The transit of Venus was claimed to have realized that a transit would indeed been observed by medieval Islamic occur in 1639, and concluded that William Crabtree watching the transit of Venus in AD 1639 astronomers. The Persian astronomer transits of Venus would occur in pairs Avicenna claimed to have observed the eight years apart. Horrocks made 24 May 1032 Venus transit of the Sun. Soon his observations from his house in after, he wrote the Compendium of the England on the 24th of November Almagest, a commentary on Ptolemy’s 1639. (Did I not say that transits of Almagest, in which he concluded that Venus took place only on Venus is closer to the Earth than the Sun. December after the year 1396 A.D? Jeremiah Horrocks (1619-1641), a The confusion arises because British amateur astronomer, could be one before 1752, Britain followed the of the two persons to observe the first old Julian system of calendar! If the recorded transit of Venus in 1639. He was present Gregorian system of one of the first Englishmen to appreciate the astronomical revolution going on in Europe following the works of Tycho, In 1627, Galileo and Kepler. It was Horrocks who Johannes first proved that the orbit of the moon is an Kepler ellipse. Horrocks died at the young age of (1571-1630), 22 and it is anybody’s guess how much using his more he could have discovered had he lived longer. Yet, he is considered to be laws of the father of British astrophysics for the planetary remarkable depth of his motion accomplishments. prepared the Johannes Kepler According to Horrocks’s Law, all the Rudolphine then-known planets would appear the same size if viewed from the Sun. Not true tables SCIENCE REPORTER, MAY 2012 10 Cover Story Jeremiah Horrocks with his telescope Plaques commemorating Horrock’s achievements commemorating him were installed in The Perhaps the transit of Venus during atmosphere, and indeed it was held to be Parish Church of St Michael, Much Hoole.