Transit of Venus

A transit of Venus (from the Latin transitus, passage ',' pre-transition '), and the transit of Venus or Venus Passage, is a pre- pull of the planet Venus across the sun. The with a telescope, sometimes freiäugig (with filter glasses) observable phenomenon occurs in about 243 years only four times ( after 8, 121 additional ½, an additional 8 and 105 other ½ years ) because Venus and Earth's orbit are inclined towards each other a little.

After the Venus passages of the 1874, 1882 and 2004 took place between about 0:00 to 7:00 clock clock CEST last June 6, 2012. The next step will only occur again on December 11, 2117.

The Venus Transit at an apparent diameter of 1 ' (1/ 30 of the solar disk ) and appears completely black in contrast to the sunspots. Historically had the precise measurement of such passages of great importance for determining the distance between Earth and Sun ( astronomical unit ) and gave rise to many expeditions and measuring campaigns of major institutions and scientists. Since 1900, the distance was determined by means of near-Earth asteroids in the solar system (NEA ) today with aerospace and radar methods.

  • 4.1 History of the solar
  • 4.2 Halley's method
  • 5.1 1761
  • 5.2 1769
  • 5.3 1874
  • 5.4 1882
  • 6.1 8 years
  • 6.2 243 years
  • 6.3 121.5 and 105.5 years
  • 7.1 Roaming Transit
  • 7.2 Simultaneous transits

Basics

For a Venus transit the Sun, Venus and Earth are exactly in line. The principle of this rare planetary constellation is the equal of a solar eclipse, when the moon moves in front of the sun and darkened it. However, a Venus transit calls because of the large distance between the Earth and Venus no noticeable darkening on the earth bring forth. The Venus covers as opposed to the moon from only a tiny fraction (about one-thousandth ) of the solar surface. She wanders seemingly as tiny deep black disk in the course of several hours west of the sun.

The penultimate Venus passage occurred on 8 June 2004. For Vienna or Frankfurt am Main it lasted from 7:20 bis 13:23 clock clock CEST. At the time of transit, the distance between Venus and the Earth was more than 42 million kilometers from Venus to the Sun about 109 million. Because of the good weather, the phenomenon could be observed in large parts of Europe. To this end, a prism binoculars or a telescope was not absolutely necessary; a protective film for the eyes was enough. There were also coordinated parallel measurements take place in South Asia and Australia.

A transit of Venus is a very rare event, of which there are 130 in just two years, alternately within a short distance of eight and a long distance of about 100 (depending on node 105 or 122 ) years. The distance between five transits is thus periodically and is about 243 years, 1 day and 22 hours. The final was held on June 5th and 6th, 2012, the penultimate on 8 June 2004, whose predecessor was observed on 6 December of the year 1882. In the 20th century, not a single transit of Venus took place. A transit of Venus is therefore actually an astronomical event of the century and, by its very rarity of observing a worthwhile sky spectacle. However, one has to necessarily appropriate, heat- safe sunscreen use, since one could go blind otherwise.

Cause of the rarity of the transit of Venus is the inclination of the orbit of Venus relative to the Earth's orbital plane by 3.4 °. Therefore, the Venus is not in any inferior conjunction with sufficient accuracy between Earth and the Sun, but runs in 98-99 of 100 cases above or below " over". With identical orbital planes could observe the transit of Venus every 1.6 years.

This inferior conjunction occurs at intervals 579-589 days when the Venus " overtakes " on her sun closer track the earth. She switches from the role of the evening star to that of the morning star. Nine months later, she is then behind the Sun ( superior conjunction ). A similar, but much more rapid cycle of 116 days ( synodic period ), the sun closest planet Mercury.

The inner planets Venus and Mercury

From Earth, seen it there are two planets, in which a planetary transit can occur: Mercury and Venus, whose orbits pass within the Earth's orbit. Similar to the Venus Transit Speak of the transit of Mercury, if named after the winged messenger planet is just between us and the sun. Mercury passages occur much more frequently than at Venus - alone in the 21st century, there are fourteen: The first of these took place on 7 May 2003, the 14th will occur on November 10, 2098. While play Venus passages in our epoch in the months of June and December, see Mercury passages held in May and November. This is due to (node ​​) with the position of the orbital planes and their intersections. However, the lines of intersection between the planes of Earth and Venus train move slowly, thus shifting the timing of the Venus transits slowly at later dates in the year. Thus, from the year 4700 Venus passages in January and July and no longer be held in December and June.

Sequence of a transit of Venus

A transit of a planet from the sun has four contacts.

The first contact is the contact of the planet disk with the sun. A few seconds later you can see, knowing the exact location on the solar disk, the indentation. As a second contact is defined as the time when the slice is completely from the sun and still no piece between sun and planet wheel rim can be seen. After that, the planet wanders seemingly ahead of the sun. The third and fourth contact is the inverse of the second and first contact. Since we know the exact location of the planet from the disk on exit, the exit can be observed exactly to the end.

Shortly before the second and after the third contact of the Lomonosov effect is observed, which is due to diffraction of the sun rays through the upper layers of the atmosphere of Venus.

Immediately after the second and before the third contact can often be observed dripping phenomenon. When observing through a telescope or to photos, Venus does not appear circular, but the sun the edge deforms like a drop. However, the cause of the phenomenon is not - as asserted earlier - the proof of the dense atmosphere of Venus, but lies in the limited resolution of each necessary for observing optical arrangement, as they constitute a camera lens or a telescope.

Past Venus passages

Johannes Kepler had predicted the first time a transit of Venus, those of 1631. But he was not to be seen from Europe, there stood for all European observers the sun at the time of the passage below the horizon, and the scientific potential of the event was not detected. Kepler died in 1630, the subsequent passage of 1639 could not be predicted with the Kepler orbit data, because they were too vague by a few hours. The Englishman Jeremiah Horrocks was in calculations in October 1639 on the basis of Kepler and other data to identify and correct these inaccuracies and noted that a further passage would soon follow. This transit of Venus on December 4, 1639 was the first to justify observed, from Jeremiah Horrocks and William Crabtree himself. In the short preparation time Horrocks was only his friend Crabtree alert in time for a second observation.

In astronomy, we learned quite early to measure angular distances between astronomical objects with increasing accuracy. But what you could not at first measure, were the distances of the heavenly bodies. As soon as they had once determined such a distance, so that the remaining distances in the planetary system could be determined as the ratios of the planetary distances were already known to each other due to the third Kepler 's law.

It was customary to express the distance to the sun through the horizontal parallax, that is, by half the angle at which the sun moved in front of the fixed star background appears when it is viewed simultaneously from two located opposite on the earth places (appears under the whole angle also the diameter of the Earth from the Sun as viewed ). The modern value of the half angle is 8.794148 ", according to a length of 149,597,870 kilometers for the astronomical unit.

History of the solar

Aristarchus was the first one in principle correct method, based on the angle in the rectangular at half moon triangular earth-moon - sun to determine the solar parallax, but received the unsatisfactory from today's perspective result that the sun is more than 18 times but less than 20 times far away as the moon ( in reality it is about 390mal so far ). Hipparchus calculated from the geometry of a lunar eclipses already significantly better solar parallax of 3 '. This value was traditionally used until the late 16th century. Kepler observed in the study of Tycho's Mars observations that the former means no Marsparallaxe was measurable, so that even smaller solar parallax could not be greater than 1 '. The Mars opposition of 1672 was observed simultaneously by Jean Richer in Cayenne and GD Cassini in Paris, which is a solar parallax of 9 ½ " ableiteten from the measured Marsparallaxe, albeit with considerable scatter of individual values ​​. Lacaille was his 1751-1754 at the Cape of good Hope salaried position measurements of Mars and Venus compare with European observations and obtained a solar parallax of 10.20 ". These and all other Parallaxenbestimmungen (most at Mars oppositions ) but were always on the edge of measurability, so that as a consensus could only establish the view until the 18th century, the solar parallax must be less than about 15 ".

Halley's method

The transit of Venus was the first historic opportunity to determine distances in the solar system precisely. It was observed from the transit of various points on the Earth, which lie as far apart in north-south direction. From different points of view, it was observed that by Venus was different near the center of the sun as viewed from the north pole of a little lower, from the South Pole of slightly higher ( " parallax "). In the end, could be calculated from the sun from the known distance between the observation points on the earth, the distance of the earth.

Edmond Halley in 1716 had recognized that during such a transit, the parallax of Venus instead of angle measurements could be determined by time measurements much more accurate and even. The diagram shows an example of the positions of Venus across the solar disk during the transit of 1769, as observers in Tahiti ( Pacific) and presented themselves in Vardo (Norway). Seen from Tahiti went through Venus because of the observer location in the southern hemisphere a northerly and thus shorter tendon on the solar disk. The lateral offset of both tendons was determined by angle measurements, but especially by comparing the observed at both locations transit time.

In addition, the Venus from Tahiti seen apparently moved quickly across the solar disk as seen from Vardo from, because the observer on Tahiti was located closer to the equator and during the observation due to the Earth's rotation back put a larger arc. In addition, Vardo was located during transit on the sunny side of the earth facing away from the midnight sun, however, was able to observe over the pole time. While Vardo as a result of Earth's rotation in the same direction as the moving earth overtaking Venus, Tahiti was worn in the opposite direction. Thus, the apparent velocity of Venus has been reduced front of the sun for Vardo, enlarged for Tahiti, however. Was also the reason why the observer on Tahiti, the entry of Venus and later her exit earlier than the observer in Vardo.

The difference between the Venusparallaxen for the two observers could therefore be determined by time measurements that were then in principle already possible with seconds precision. The comparison of several possible parallax of two distant observers at known locations then allowed to determine the distance to Venus by triangulation. The results of the evaluations were the diameter of the sun and the radii of the planetary orbits of Earth and Venus. The mean radius of the Earth's orbit was henceforth used as astronomical unit AE especially when size information within the planetary system. With one of the two specific planetary orbits and the easy and secure determinable periods of the planets could be calculated with the help of Kepler's third law, the radii of the other planetary orbits. Since it was expected to observe the period of contact with an uncertainty of only a few seconds, a transit of Venus would have allowed to determine the solar parallax at least 1/100 " exactly.

Since Halley's method required to measure the duration of the entire transit, their application was limited to those observing sites, both the inlet and the outlet were visible for. Delisle worked out a method that could also evaluate the observation that individual transit phases, provided templates for a phase observations from at least two locations. This reduces the number of possible observation sites has been greatly expanded. However, Halley's method had the advantage assume no precise knowledge of the length difference of the compared stations, while for Delisle's method, the coordinates of the observation site - had to be measured as precisely as possible - especially the then only with great effort on determining longitude.

The Venus passages in the 18th and 19th centuries

1761

According to the suggestion by Halley and Delisle especially later expeditions were sent out to some very remote places. So traveled Le Gentil to Pondicherry in India ( where he arrived because of political turmoil after the passage, then in the land remained to observe the passage of 1769, but was prevented by clouds on it), pingre to Rodrigues Island east of Madagascar, Maskelyne to St. Helena, Planman to Kajaani, Chappe to Tobolsk, Rumowski after Selenginsk. Together with other expeditions and numerous European observers finally lay before useful results from a total of 72 stations.

In order for the solar parallax was first clearly brought the range of measurability. Due to the disparity of instrumentation, different observation methods, but especially the unexpected drop phenomenon, which made ​​the time of the second and third contact very uncertain, but the accuracy of the results fell far short of expectations. Pingre received in his analysis, for example, 10 ½ " Short 8 ½ " Hornsby 9 ¾ ", etc.

1769

Also for this passage numerous expeditions were fitted again. How about watching James Cook, accompanied by Green and Solander in Tahiti, Alexandre Guy pingre in Haiti, Jean Chappe on Baja California, Rittenhouse in Norriton and the Vienna court astronomer Maximilian Hell most northern observers in Vardo. Euler organized a large observation network in Russia. A total of 77 stations yielded usable observational data.

The results were much better time from different analyzer were, however, due to different calculation methods, and different ways to combine the data, still significantly differing results, as for example

Encke underwent all of the data from 1761 to 1769, a joint analysis using the newly developed curve fitting and received a solar parallax of 8.578 " ± 0.077 ", according to an astronomical unit of 153.4 million kilometers.

1874

The transit of Venus of 1874 was relatively unfavorable. He stayed almost the whole of Europe invisible, long transit times were observed only from Asia and short transit times from Australia and the South Sea Islands from. Nevertheless, about 60 expeditions were sent out to collect at least experience with the more modern instruments again. It must, however, be noted that the contact points in time by ten seconds and more or less different with uniform instruments provided observers in the same place, and that the first time applied the photographic position measurements lagged the accuracy of traditional micrometer measurements.

1882

In preparation for the passage of 1882 an International Commission adopted proposals for uniform instrumentation and observation methods. Particular, it was established that in the event of the occurrence of a phenomenon, the drops should be ( at the entrance ) and his first-time show ( at the exit ) to be determined time points the final rupture of the " band ". It took about 38 expeditions on the road, mainly in the northern and southern parts of the American continent.

Newcomb, had its processing of the passages from 1761 to 1769, a solar parallax of 8.79 " ± 0.05 " result, obtained by adding the data from 1874 and 1882, a value of 8.79 " ± 0.02 ". Thus, the method of Venus passages was significantly lagged behind the expectations of the astronomers, and even behind the observation of Mars oppositions: Gill had from the Mars opposition of 1877 a solar parallax " ± 0.01 " obtained from 8.78.

In 1896, astronomers agreed during a conference on it to use for consistency for the ephemeris one obtained from the Venus passages and other provisions mean 8.80, " according to an astronomical unit of 149.5 million kilometers.

In the 20th century there was no Venus transits, we refined the results using near-Earth asteroid Eros positions of the opposition, during which parallax measurements could be obtained. While the opposition 1900/1901 Eros approached the earth up to 48 million km; the parallax measurements provided a solar parallax of 8.8006 " ± 0.0022 " ( AE: 149 488 000 ± 38,000 km ). An even more favorable opposition led Eros in 1931 even up to 26 million kilometers of the Earth zoom; the observations from 24 observatories revealed a solar parallax of 8.7904 " ± 0.0010 " ( AE: 149 675 000 ± 17,000 km ). For 40 years, the distances are measured in the planetary system with radar.

Periodicity

The earth needs a sidereal year of TsidE = 365.256 days to orbit the Sun once; Venus needs TsidV = 224.70 days. It follows that a certain position of the two planets to each other - for example, the inferior conjunction - after a synodic period of the Middle TsynV = 583.9169 days repeated.

8 years

Thus, although the Venus (on average) almost all 584 days passes its inferior conjunction, it still pulls rarely over the solar disk. Since the orbit of Venus is tilted by 3.4 ° from the Earth's orbit, the Venus - seen from Earth - go by the sun during an inferior conjunction at a distance of more than 8 ° (16 Sun's apparent diameters ). This happened a transit of Venus, the Sun, Venus and Earth have almost exactly standing in a line, Earth and Venus must therefore also close to the common intersection of their orbital planes ( the so-called line of nodes ) are. The earth crosses the line of nodes to June 7 ( in this node passes through the Venus, the Earth's orbital plane from north to south, " descending node " ) and by December 6 ( from south to north, " ascending node ").

Find a Venus transit on a given date take place, the next opportunity for a passage eight years later. Then, on the one hand is an integer number of earth years elapsed ( that is, eight: 8 × TsidE = 2922.0480 days ), the earth is so again in nodes nearby. On the other hand, this period corresponds almost exactly to an integer number synodic Venus periods (namely, five: 5 × TsynV = 2919.5845 days ) and the Venus goes through a inferior conjunction again, so is again close to the Earth and thus also returned to nodes nearby.

After four uneventful bottom conjunctions in other parts of the tram so Earth and Venus meet in the fifth again in successive nodes nearby. However, the coincidence is not exact, because the earth is 2.46 days it takes longer to reach the node again when Venus takes to reach the conjunction again ( 2919.5845 2922.0480 days compared to days ). During the conjunction of Venus and Earth are thus still a piece of nodes removed, and the Venus appears around 22 arc minutes north (if the descending node ) or south (if the ascending node ) as the last pass.

Went the last pass centrally through the solar disk, the Venus missed in the new opportunity now occurred as sun, as they are now 22 ' north or south stands, the solar disk but only a radius of 16'. However Went the last pass far enough south (or north ) by the solar disk, so that it is not made even after a shift to 22 ' to the north (or south), as happened again a passage, this time by the other sun half. The next opportunity for another eight years later, the sun is but then misses necessarily ( the shift by 2 × 22 ' is larger than the solar diameter of 32'). Venus passages thus occur either singly or in a pair distance of eight years. Then drift node passage and Conjunction getting wider, so that for some time there can be no passage.

243 years

A longer period, up in the sidereal and synodic Venus Earth years periods each almost exactly a whole number, is 243 years old: 243 × 152 × TsidE ≈ TsynV. 243 years after passage so happened again a passage in similar circumstances. For example, the passages from the June 3, 1769 and June 6, 2012 nodes were both held on the descending and ran through the northern part of the solar disk.

121.5 and 105.5 years

While the place of the conjunction in the course of its above -mentioned drift orbits the train, but it also applies to the opposite node and allows there also passages. The periodicity of the passageways must be expressed by a half-integer number of sidereal earth years and an integral number of synodic periods of Venus in these cases. Possible combinations are for example 121.5 × 76 × TsidE ≈ TsynV and 105.5 × 66 × TsidE ≈ TsynV. Other pairings are likewise conceivable (eg, 113.5 × 71 × TsidE ≈ TsynV ), but can not occur here, since the sub-periods must add up to 243 years. This is (currently ) by the appearance of the sub-periods 8 105.5 8 121.5 = 243 the case.

In the long term face due to the changing planetary orbits other periodicity a. The graph shows all lower conjunctions of Venus for the year -18 109 to 21988; the millennium 2001-3000 is highlighted in gray. Conjunctions without transit are shown as bright dots, conjunctions with transit as dark spots. Each line consists of 152 conjunctions, the number of conjunctions in a transit cycle of 243 years. During the period of 243 years is maintained, resulting in the passage of time different divisions into sub- periods.

During the period of May 22, 427 BC to 23 November 424 AD were both 8 -year pairs replaced by some individual transit, the periodicity was 121.5 121.5. Then each of the May passages occurred in pairs, during the November passages remained individually. The current pattern 8 105.5 8 121.5 began on December 7, 1631 and will end on June 14, 2984. On 18 December 3089 a series will begin in June paired passages and each December passages; this pattern 129.5 8 105.5 will end on 25 December 3818.

Special forms for the transit of Venus

Roaming Transit

It is in principle possible that Venus passes in a transit at the solar limb. It may happen that Venus completely and others only partially from the sun moves past for some areas of the world. Such passages are very rare: last such a passage on December 6, 1631 took place. The next such transit of Venus will occur only on December 13, 2611.

It is also possible that a transit of Venus from some areas of the Earth is visible as a partial transit, while passing by observers in other parts of the world, the planet Venus to the sun. The last such transit took place on November 13, Greg. 541 BC against 13:36 clock (UT ) instead, the next such transit of Venus will occur on December 14, 2854.

Simultaneous transits

The simultaneous occurrence of Mercury and Venus passages is not in the near future and the past due to the different node position possible. However, the position of the web node changes slowly. Since the web node of Mercury and Venus move at different speeds, such events are possible in the distant future, but only in the year 69163, and in 224,508th contrast, the simultaneous occurrence of a Solar eclipse and a Venus passage is already on 5 April 15232 possible.

On June 4, 1769 a total solar eclipse that was seen in Europe, the northern parts of North America and North Asia at least as a partial eclipse occurred just five hours after the end of the transit of Venus. This was the smallest time interval between a planetary transit and an eclipse in historical times.

Observing Hints

From observations of the sun or of a planet transit with the naked eye or with self-made filters is absolutely not recommended. With homemade filters from unaudited materials, there is no certainty whether harmful, but invisible ultraviolet and infrared components of sunlight are filtered out. Above all, you should never visible to the naked eye (even with sunglasses or the like ) seen through a prism binoculars or a telescope at the sun because the sunlight is so highly collimated that the retina of the eye immediately destroyed, or is severely damaged. In direct observation through a telescope necessarily suitable solar filter in front of the lens - used - not only in front of or behind the eyepiece.

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 holds the paper in 10-30 cm of space behind the eyepiece. The sun will appear as bright circular area and is focused by rotating the eyepiece. Venus or Mercury migrate as small, dark slices in the course of hours over the surface of time.

This projection method is also very suitable for the observation of sunspots. In this case, however, one must be careful that the telescope does not overheat, which lenses or mirrors would burst. The finderscope of the telescope must be covered because the focused radiation of the sun is sufficient to destroy the crosshairs of the viewfinder or burn holes in your clothes.

Also there Observatories at Venus transits (as well as other important astronomical events ) the possibility of observing the process with the help of professional tools.

Pictures of the course of 8 June 2004

7:49 clock: Venus just completely on the solar disk

10:19 clock: Venus in the middle of their path in front of the solar disk

12:33 clock: Venus approaches the eastern limb of the Sun

13:10 clock: Venus almost on the eastern limb of the Sun

13:13 clock: Venus above the limb of the Sun 13:29 clock: Venus exits the solar disk

10:10 and 13:09 clock: Venus transit images in high resolution, including Lomonosov ring

13:29 clock: Venus exits the solar disk

Pictures of the course from June 6, 2012

Gera / Thüringen Germany Clock 05:38 (UTC 2)

Finsterwalde / Brandenburg Germany Clock 06:10 (UTC 2)

Jeßnigk / Brandenburg Germany Clock 06:14 (UTC 2)

Wiener Neustadt, Austria Clock 6:19 (UTC 2)

Schleswig -Holstein Germany Clock 6:23 (UTC 2)

Lower Austria Austria Clock 6:32 (UTC 2)

Vienna, Austria 3 Contact Clock 06:37 (UTC 2)

Vienna, Austria Transit - end Clock 06:50 (UTC 2)

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