Transit of Mercury
A transit of Mercury (from the Latin transitus, passage ',' pre-transition '), also Mercury transit or Mercury Passage, is a pre- pull of the planet Mercury from the sun. This Mercury migrates as a tiny black dot within several hours across the solar disk. Overall, it is 13 - or 14 times per century to a Mercury transit. Because of the small apparent size of the planet can not be seen with the naked eye a transit of Mercury. As the first man Pierre Gassendi observed on November 7, 1631 a Mercury transit.
In addition to a transit of Mercury can be observed from the Earth, a transit of Venus, since the orbit of Venus around the Sun - like that of Mercury - is within that of the Earth.
- 5.1 General Information
- 5.2 Mercury transit Dates 1950-2050
Basics
In a transit of Mercury Sun, Mercury and Earth are almost exactly in line. The principle of this rare planetary constellation is similar to a solar eclipse, when the moon moves in front of the sun and darkened it. Unlike a solar eclipse, a transit of Mercury, however, calls forth no noticeable eclipse on Earth, because the Mercury only - depending on the distance from the earth - between 0.026 ‰ and 0.043 ‰ of the solar surface covered. For solar eclipses the moon may obscure the whole Sun. Mercury can be seen from Earth during the transit as a tiny dot ( with magnification as small disc ), which travels within several hours from east to west across the solar disk.
The constellation in which a transit can occur is called inferior conjunction. Since the Mercury with a sidereal orbital period of 88 days significantly faster around the sun than the Earth, it comes about every 108-130 days at no additional that the Mercury Earth " inside outdated ". However, an inferior conjunction does not automatically lead to a transit, as the Mercury's orbit is inclined about seven degrees to the Earth's orbit and the planet thus at a lower conjunction usually passes above or below the sun disk. The Mercury's orbit intersects the Earth's orbit only in the two so-called railway junction. So order the Mercury can pass in front of the sun, must take place in the immediate vicinity of one of the two nodes one inferior conjunction.
Unlike Venus, with just under 225 days, a significantly longer circulation time than Mercury, come Mercury passes per century 13 - to 14- times before, during Venus passes only every 100-year old (and mostly in pairs with a distance of about eight years occur between the two transits ). A transit of Mercury can be a distance of 3 ½, 7, 9 ½, 10 or 13 years to the previous transit have. Here, the cycle of Mercury passages is significantly more complex than that of Venus passages, as the Mercury has an exceptionally high eccentricity of 0.2056. One cycle of Mercury passages repeats itself every 46 years. In this time are 46 rounds of the earth around the sun counter 191 rounds of Mercury. Then Mercury is from the Earth seen again at exactly the same position, the deviation from this cycle is only 0.34 days.
The two nodes of the orbit of Mercury are located at about 46 ° and 226 ° ecliptic longitude, where the earth is about on November 10 and on May 7. Transits at the ascending node thus in November, those on the descending node in May. In this case, a clear difference between the frequency of transits to the two nodes can be observed. During occur about two-thirds of all Mercury passes the ascending node in November, accounting for only a third of May and hence on the descending node. This is justified also by the high eccentricity of Mercury's orbit. In a passage in November, Mercury is farther from the earth than in a passage in May. This one passage is still possible than with inferior conjunction in May at a greater distance of Mercury to the intersection station during inferior conjunction. As slowly move the rail hub of the planet Mercury to larger values of ecliptic longitude, also move the dates for the Mercury passes over the centuries to ever later calendar data. Thus, for example, from the year 3426 Mercury transits take place in June and December.
In addition transits last longer than in May - November transits, as the Mercury at the May transits almost at sonnenfernsten point of its orbit, the aphelion, is thus almost has its smallest possible speed. In contrast, Mercury is in November transits only a few days before the perihelion, the closest to the Sun point of its path, and thus has almost its maximum possible path velocity. Again, the high eccentricity plays a role, as the web speed in the course of a cycle is more variable at higher eccentricity as a consequence of Kepler's second law. At perihelion, the path velocity of the planet at 59 km / s over 50 % higher than at aphelion ( 38.9 km / s).
The last transit of Mercury was held on 8 November 2006, however, was fully visible only from Oceania and the west coast of North America from. In Europe, the time of transit fell into the night and was therefore not observed there. The last Mercury transit, which was to follow completely from Europe, took place on the morning of May 7, 2003 and lasted for about 5 h 20 min. The next transit will take place on May 9, 2016 and this will be fully visible in Europe.
Expiration of a Mercury transit
During the transit of Mercury, a distinction - as with any transit of a planet from the sun - four contacts:
The first contact, the first contact of the small planetary disk with the sun, and thus the beginning of the transit represents only a few seconds later is given knowledge of the exact location on the edge of the sun the associated indentation recognizable. As a second contact is defined as the time at which the Mercury disc for the first time completely faces the sun and detaches from the solar limb. The phase between the first and the second contact is referred to as an entry, but it lasts for a transit of Mercury only between one and four minutes. After that, the planet wanders seemingly ahead of the sun. The third and fourth contacts represent a reversal of the first two contacts dar. the third contact of the discharge, which is terminated with the fourth contact, while also addressing the whole transit ends begins.
Can Immediately after the second and just before the third contact - as well as with a Venus transit - even with a Mercury transit the drop phenomenon (english black drop effect) can be observed.
The Mercury passages of the years 1999 and 2003, took advantage of three American astronomers to detect a drop phenomenon, as it was known primarily of Venus passages so far, even with Mercury transits. They used the space telescope and TRACE observed this phenomenon, despite the fact that it is outside the Earth's atmosphere and the Mercury has no atmosphere. In previous Venus passages (most recently 1882) was considered the drop phenomenon primarily as evidence of the atmosphere of Venus. Applying the results of the observation of Mercury passages of 1999 and 2003, the Venus, this claim has been refuted. Today it is known that the drop phenomenon is caused by the limited optical resolution of the telescopes used.
Historic Mercury passages
Since a transit of Mercury with the naked eye is not observable by optical aids without magnification, was before the invention of the telescope in the early 17th century, in all likelihood, no transit of Mercury was observed. So thought of living in the 12th century Moroccan astronomer Alpetragius, Mercury is transparent, because you never see him pass in front of the sun. However, there have also been several observations that were incorrectly interpreted as a transit of Mercury, for example, a sunspot, which was for eight days to see in the year 807 on the sun.
The first exact calculation of a Mercury transit succeeded the German astronomer Johannes Kepler in 1627 using the completed Rudolfine Tables, in which he predicted the planetary positions significantly more accurate than they were given in the tables previously used. He said using the boards require a Mercury transit for 7 November 1631 in which his calculations differed by only about five hours off transit. However, Kepler died in November 1630, and therefore could not even watch the transit of Mercury. On November 7, 1631 Frenchman Pierre Gassendi was observing ( at the same time as two other people in other locations ) of Paris from the Mercury transit. He determined the diameter of Mercury with about 20 arc seconds, which was below the previously determined by Tycho Brahe value of 130 seconds of arc significantly. Johannes Hevelius measured the transit of Mercury from 1661 an even smaller diameter than Gassendi. He also saw the appearance of the transit on the date on which the calculated based on elliptical orbits panels had predicted, as a proof of the correctness of the first Kepler 's law, according to the planets move in elliptical orbits around the sun.
On November 7, 1677 that the British astronomer Edmond Halley, make accurate measurements of taking place at this time Mercury transit. At this time he was on the Atlantic island of St. Helena, there to create a catalog of the stars of the southern sky. He also remarked on this passage, that such a being suitable to calculate the length of the astronomical unit ( the distance between the Sun and Earth ) exactly. However, he noted that the Mercury disc is too small to obtain accurate results and, instead, a Venus transit would be better suited for such a project. This was later confirmed by French astronomers who observed the Mercury passes between 1723 and 1753 and also reached very inaccurate results.
Thus, the focus was more on subsequent transits primarily investigated whether the planet has a moon, also was looking for evidence of an atmosphere, trying to identify other phenomena in a Transit on the small disk of Mercury itself Man. The search for a moon was soon replace in the background, since the existence of a moon was considered very unlikely.
Until the Mariner 10 spacecraft in March 1974 as the first space probe reached Mercury and thereby found that the planet has no atmosphere, was the search for evidence of an atmosphere of the planet one of the main scientific goals for the observation of a transit of Mercury. When Mercury transit of 1736 a French observer noted a shiny ring around the black disk. This observation was confirmed in 1799 by several observers ( including was the German Johann Hieronymus Schroeter ); and 1832, when it was reported by a ring with a violet tint, and 1868, when William Huggins thought he saw a light shell, which was about half as wide as the apparent diameter of the planet. These phenomena are not finally resolved until today, but no atmosphere of this can be blamed. It is thought that these observations are due either to the diffraction or by the inaccuracy of monitoring instruments can be explained by the drop and the phenomenon is caused.
Huggins observed in 1868 next to the light cover a luminous point on the Mercury disc. Also, this observation has been handed down throughout history several times. The first mention of such a point on the Mercury disc by the German Johann von Wurzelbau in 1697. During Mercury transit of 1799 Schroeter observed and his assistant Karl Ludwig Harding grayish spots on the disk of the planet, even at later passages similar observations by other astronomers have been made. Since the late 19th century, however, reported more of any such observation, so that it is probably due to inaccurate optics.
Due to more modern techniques and the space through which the Mercury can be accurately observed and measured, the scientific importance of Mercury transits is still low today. In recent history, the previously mentioned observations of 1999 and 2003 were thus the most significant, as these provided the evidence that the drop phenomenon is not caused by an atmosphere by could be detected in an object with no air cover as well.
Special forms of Mercury transit
Central transit
If one calculates the average of all previous transits since 1600, had the Mercury disc an average minimum distance of at least 500 seconds of arc (8 ' 20 ") from the center of the solar disk. That's about 45 times the apparent size of the planet from the sun (11 ") and about a quarter of the apparent size of the sun (32 ' ) itself so Mercury moves into his average minimum distance about halfway between the center and the edge of the sun over.
In the past four centuries, there were a total of five Mercury transits that passed in its minimum distance is less than 100 seconds of arc (1 ' 40 ") at the center of the sun. The next was the center of the transit of 10 November 1973 who had a minimum distance of only 26.4 seconds of arc to the center and thus a central transit came very close. A transit, in which the small disk of the planet crosses the center of the sun, although theoretically possible, but statistically almost impossible due to the small size of Mercury.
The next transit of Mercury, which will pass with a minimum distance of less than 100 seconds of arc at the center of the sun will take place already on 11 November 2019 where Mercury is closer to the center up to 75.9 ". The transit on November 12, 2190 will be with a minimum distance to the center of 9.1 arc seconds of the most central transit of this millennium. The last transit of Mercury with an even smaller distance (7.2 arcsec ), however, took place on 21 April 1056.
Roaming Transit
In principle it is also possible that the Mercury moves along exactly at the solar limb. Such transit is called a grazing transit. Overall, 2.8 % of Mercury transits are grazing, calculated over a period of half a million years.
When grazing Mercury transit on 15 November 1999, the Mercury wandered completely for some areas of the world, for others only partially past the sun. The second last such transit took place on 22 October 1559. The next transit of Mercury in the Mercury for observers in some areas only partially before the Sun enters, but in other completely, will be held again until the May 11, 2391. Grazing transits of this type have a share of about 1.1 per cent of all Mercury passes.
Moreover, it is possible that a Mercury transit of some areas of the earth is visible as a partial passage, while the planet for an observer passes by in other parts of the world at the solar limb, and thus is not observable. Such a transit occurred last one on May 11, 1937. The penultimate event of this kind was on 21 October 1342. The next Mercury transit, which will be for observers to see in some parts of the world as a partial transit, while just passing by in other parts of the world Mercury to the Sun, is only on 13 May 2608 enter. Calculated over half a million years to come grazing transits of this type with a share of 1.7 % of Mercury passages somewhat more common than the other type.
Simultaneous transits
As Venus and Mercury have different node lengths, a simultaneous occurrence of Mercury and Venus transit in our time is not possible. Currently, the railway junction of Mercury and Venus are about 28 degrees apart. However, the railway junction lines of Mercury and Venus do not migrate at the same speed. The railway junction line of Mercury moves slightly faster than that of Venus, which migrates to about 0.9 degrees per century with a change of 1.2 degrees per century. Over the next centuries, the node of Mercury's orbit where the orbit of Venus approaching so on and on, so that a double transit would be possible in about 10,000 years. The astronomer Jean Meeus of Belgium and Aldo Vitagliano of the University of Naples Federico II in Italy calculated that the next simultaneous transit of Mercury and Venus will occur only in the year 69 163. The following fact will be held only 224 508. In similar calculations based on the past millennia they found out also that there was no simultaneous passage of the planets from the sun in the last 280,000 years.
The simultaneous occurrence of a Solar eclipse and a Mercury passage is theoretically possible earlier due to the faster moving lunar nodes. Due to the rarity of both events, however, such an event is extremely rare; it will occur only on 5 July 6757 and be on display in the south of the Pacific. In this eclipse but it is only a partial. On July 20, 8059, a transit of Mercury is, however, occur simultaneously with an annular eclipse. The next transit of Mercury, which occurs simultaneously with a total solar eclipse will take place only on 11 August 9966.
Observation
General information
Observations of the sun or of a planet transit with the naked eye or with self-made filters can cause permanent eye damage and even blindness. With homemade filters from unaudited materials can be no assurance that harmful, but invisible ultraviolet and infrared components of sunlight are filtered out. In particular, you should never look at the sun with binoculars or a telescope without optical sun filter as the burning glass effect of the device would destroy the eye immediately.
A transit of Mercury can be without optical magnification not observe a solar eclipse goggles or the like, as the Mercury with an apparent average size of 11 arc seconds ( approximately 175 times smaller than the apparent diameter of the Sun) is too small to be seen without magnification. Therefore, NASA recommends a telescope with a 50 - to 100-fold magnification. However, this telescope must be equipped with a special solar filter, which is attached to the lens, but not downstream of the eyepiece, as there the heat would be too large. The easiest way to perform solar observations by projecting the solar image on white paper. This one aligns the telescope by its shadow on the sun and holding a sheet of paper in 10-30 cm of space behind the eyepiece. The sun appears as a bright circular area and is focused by rotating the eyepiece. Mercury then migrates as a small, dark slices in the course of hours over the surface of time.
The last Mercury passes were also transferred from multiple sites via webcam, including in 2003, the European Southern Observatory.