Simulation of simultaneous transit of Mercury and Venus across the disk of the Sun on July 26, 69163. Mercury is the small dot in the upper left. Source: Journal of the British Astronomical Association, 2004
The transit of a planet across the Sun, like that of Mercury from Monday, May 9, is always a fascinating phenomenon: it offers us a perspective unusual, without mediation, the ecliptic dynamics and our place in the solar system. From the Earth, the planets passing across the sun, we can observe only two. The two innermost orbit than our Mercury and Venus . The first with an average rate of around the dozen years, the second much more rare – the last time was three years ago, and next we will have to wait until 2117.
But will ever happen to see them pass along ? Two spots simultaneously on the solar disk? Well, the answer is yes. Or rather, not us, but our descendants yes: the rare celestial condition is scheduled for Friday, 26 July 69163 . That is to say, over 671 centuries. And to determine it has succeeded for the first time, in 2004, a pair of scientists including an Italian: the Belgian meteorologist Jean Meeus and Aldo Vitagliano , a professor of chemistry University Federico II of Naples.
on 26 of July 69163. the date of the next simultaneous transit of Venus and Mercury across the Sun. Vitagliano Professor, what is it that makes this astronomical event so rare?
“Oh, yes, it’s a really rare event. It can be estimated to occur no more than 5 or 6 times over a million years. Because a planet appears to us passing across the solar disk, it is necessary that just at the time of inferior conjunction with the Sun, the planet is in close proximity to one of the two points (the “nodes”) in which its orbit intersects the ecliptic plane . The approximate coincidence of the conjunction with the transition from a node is already set to be an event not too frequently (in 1000 years we have on average 165 13 transits of Mercury and Venus), but to have a simultaneous transit of two planets must have four coincidences. Meanwhile, one of the nodes: the plans of the two orbits must cross the ecliptic plane roughly along the same line. Then, for both, you must have the coincidence of the conjunction with the transition from the node. And finally the two conjunctions should occur simultaneously, with a tolerance of a few hours. “
At the moment, the situation in which we are?
“Currently the nodes of the orbits of Venus and Mercury are within 28.3 ° along the ecliptic. The transits of Mercury can only occur about a month away from those of Venus: the first half of May and November for Mercury, and the first half of June and December for Venus. Therefore simultaneity is obviously precluded. But the lines of the nodes of the planetary orbits revolve slowly over time, with different speeds, and those of Venus and Mercury are approaching, with a half period that varies between 50 and 55 thousand years (overlapping each 50-55mila years). Next you will overlap in the 13th millennium: that is to say, between the 11th and 15th millennium, the nodes of the two planets will be close enough to offer the possibility of a simultaneous transit. But it should also be present for the other three coincidences mentioned above, which, however, will not occur. It will be necessary to wait until the next favorable period, 55 thousand years later, and toward the end of this period the happy event will occur. Really a long gestation! “
Professor Aldo Vitagliano (courtesy)
your publication dates back to 2004. Before then, no one had been able to establish the event date. Because? No one had tried? O is also a difficult calculation?
“In a sense, both reasons. A planetary system is a system of N bodies reciprocally interacting through gravity. Until the 80′s, the calculation of planetary positions was conducted with analytical or semi-analytical methods (modern variants of Laplace methods), expressing the solution of equations of motion, not obtainable exactly, through explicit formulas consist of numerical series, the sum of innumerable periodic terms. The limit of the method is that the results are reliable only within a time span of just a few thousand years. Beyond this limit, the need to truncate the series to a finite number of terms means that the accuracy degrades rapidly, for which these methods with the provision of a such long-term transit would become extremely difficult if not impossible. “
Then what happened?
“Since the ’70s and’ 80s, the development of electronic computers has made feasible the use of numerical integration . Said in brief, means starting directly from the forces (relatively simple) into play: once they have known positions and velocities of each planet at a given instant, the mathematical model of gravitational forces allows to calculate the accelerations undergone by each, and can be anticipating new positions and velocity after a suitably short time interval. The procedure can be repeated step-by-step, so as to propagate the orbits as long as you want, with an accuracy that degrades over time much less rapidly than it does with the explicit formulas of analytical methods. The amount of calculations to be made is frightening, but it does not matter if it’s repetitive calculations and whether to get them is a machine capable of millions (today billion) operations per second.
The numerical integration was applied by NASA-JPL to the calculation of ephemeris from the end of the ’60s, under the pressure of space missions, and was mainly aimed to obtain a high precision within a relatively short time interval. The JPL mathematical models were (and are) very sophisticated, including among other things the effects on the motion due to General Relativity. I am therefore very “heavy” for the amount of calculations and ill-adapted to use over long time intervals. But there is a way to simplify them, renouncing the short-term extreme accuracy, but preserving adequately the (still moderate) who has long-term. So I would say that, as of the end of the 80s, the prediction of a transit to 100 thousand years later would be possible and even fairly simple for any researcher holding an appropriate software. “
But no one has done …
“Yeah, so you have to say that no one has thought of it. And the reason is simple: the transits are rare geometric curiosity, primarily cosmetic changes, which have taken on the public and interested above all astronomy amateurs, but they have no scientific value today if not as elegant exercise of development of the methods of calculation. It can be concluded that, to those who possessed the right tools, this type of use was not interested, while those who would be affected lacked the proper tools. My adventure began in the mid-90s, has been to build the bridge, which is the tool (the Solex program) with which any amateur with a little ‘of expertise and skills can play to flush curiosity of this type “.
Given that we are precluded, let us in the shoes of our descendants of 692esimo century. Concretely, what to see, those who will be able to witness the rare phenomenon?
“Provided that our civilization has failed to self-destruct, see (having the celestial north pole facing up) the dark disk of Venus through the circle of the Sun at the top. And near the end of the crossing, they will see the black dot of Mercury enter the Sun not far from the top, and then end their transit when Venus is already out for over an hour.
<'p > This far into the future. You have also done the calculation of the past? I mean, when was the last time that happened?“At the time I had come to 280 thousand years in the past, without unearth some. I found then that the latest simultaneous transit should have happened – adopting the calculated date with the Julian calendar, and according to a uniform atomic time, not to T.U. based on the Earth’s rotation – 17/9 / -373 172. To an age so far we are to limit the predictability of the event, but given that the planned transit is central to the disk of the Sun and is also reproduced using different models, it is likely that you have really occurred. Let’s say that having to bet, I would play the two against one. “
How come there has competed just her, which is a chemical in these astronomical calculations?
“This is not a rare case. Astronomy is the only science in which amateurs can make, and historically have given, of the relevant contributions. Just mention Heinrich Olbers, who was a doctor, William Herschel (a musician) and Percival Lowell (a diplomat). A little ‘less common are amateurs who have worked at a desk instead of a telescope (the same Jean Meeus by profession was a meteorologist, now retired for a long time), but even here there is a reason: despite my amateur interest for astronomy, I’m a daytime animal, and even as a boy I have never been able, except in exceptional cases, to stay awake after 23! “
next Monday, the transit of Mercury, there will be no need to remain standing until late at night … she will accompany him, although it will be a “trivial” transit with only one planet?
“As for the transit of Venus on 8 June 2004, will go on building solar paving of the Department of Chemistry with a binocolone 20 × 60, hoping that the weather is favorable and sunscreens built for that occasion they are still good. Then it was a success, even enjoyed by many colleagues and students. I hope it is this time. “
Learn more:
- Read the Journal of the British Astronomical Association article “Simultaneous transits”, by J. Meeus & amp; A. Vitagliano
- Go to the orbits of Solex calculation program web site developed by Aldo Vitagliano
These other Media INAF articles devoted to transit May 9:
source: Media INAF | Written by Marco Malaspina
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