Starship Asterisk*

Case wrote:http://antwrp.gsfc.nasa.gov/apod/ap0903 ... uote]Spots and blemishes on the image are background stars and camera streaks caused by charged particles.

http://en.wikipedia.org/wiki/Arthur_Eddington#Relativity wrote:
<<During World War I Sir Arthur Eddington was Secretary of the Royal Astronomical Society, which meant he was the first to receive a series of letters and papers from Willem de Sitter regarding Einstein’s theory of general relativity. Eddington was fortunate in being not only one of the few astronomers with the mathematical skills to understand general relativity, but (owing to his international and pacifist views) one of the few at the time who was still interested in pursuing a theory developed by a German physicist. He quickly became the chief supporter and expositor of relativity in Britain. He and Astronomer Royal Frank Dyson organized two expeditions to observe a solar eclipse in 1919 to make the first empirical test of Einstein’s theory: the measurement of the deflection of light by the sun's gravitational field. In fact, it was Dyson’s argument for the indispensability of Eddington’s expertise in this test that allowed him to escape prison during the war.

After the war, Eddington travelled to the island of Príncipe near Africa to watch the solar eclipse of 29 May 1919.
During the eclipse, he took pictures of the stars in the region around the Sun.



According to the theory of general relativity, stars near the Sun would appear to have been slightly shifted because their light had been curved by its gravitational field. This effect is noticeable only during an eclipse, since otherwise the Sun's brightness obscures the affected stars. Eddington showed that Newtonian gravitation could be interpreted to predict half the shift predicted by Einstein. (Somewhat confusingly, this same half-shift was initially predicted by Einstein with an incomplete version of general relativity. By the time of the 1919 eclipse Einstein had corrected his calculations.)

Eddington's observations published the next year confirmed Einstein's theory, and were hailed at the time as a conclusive proof of general relativity over the Newtonian model. The news was reported in newspapers all over the world as a major story. Afterward, Eddington embarked on a campaign to popularize relativity and the expedition as landmarks both in scientific development and international scientific relations.

It has been claimed that Eddington's observations were of poor quality and he had unjustly discounted simultaneous observations at Sobral, Brazil which appeared closer to the Newtonian model. The quality of the 1919 results was indeed poor compared to later observations, but was sufficient to persuade contemporary astronomers. The rejection of the results from the Brazil expedition was due to a defect in the telescopes used which, again, was completely accepted and well-understood by contemporary astronomers.>>

BMAONE23 wrote: Occasionally though, a comet will pass the sun and put on a real show for SOHO

http://en.wikipedia.org/wiki/Comet_McNaught wrote:
<<Comet McNaught, also known as the Great Comet of 2007 and given the designation C/2006 P1, is a non-periodic comet discovered on August 7, 2006 by British-Australian astronomer Robert H. McNaught. It was the brightest comet in over 40 years, and was easily visible to the naked eye for observers in the Southern Hemisphere in January and February 2007. With an estimated peak magnitude of -6.0, the comet was the second brightest since 1935. Around perihelion on January 12, it was visible worldwide in broad daylight. Its tail measured an estimated 35 degrees in length at its peak.

The comet entered SOHO's LASCO C3 camera's field of view on January 12, and was viewable on the web in near real-time. The comet exited SOHO's field of view on January 16. Due to its proximity to the sun, the Northern Hemisphere ground-based viewers had a short window for viewing, and the comet could be spotted only during bright twilight. As it reached perihelion on January 12, it became the brightest comet since Comet Ikeya-Seki in 1965. On January 13 and 14, 2007, the comet attained an estimated maximum apparent magnitude of -6.0, as reported by several observers in the Northern hemisphere. The comet was visible in daylight about 5°- 10° southeast of the sun from January 12 to 14, with a peak brightness of magnitude -5.5. Perigee (closest approach to the Earth) was January 15, 2007, at a distance of 0.82 AU.

After passing the sun, McNaught became visible in the Southern hemisphere. In Australia, according to Siding Spring Observatory at Coonabarabran, where the comet was discovered, it was to have reached its theoretical peak in brightness on Sunday January 14 just after sunset, when it would have been visible for 23 minutes. On January 15 the comet was observed at Perth Observatory with an estimated apparent magnitude of -4.0.

The Ulysses spacecraft made an unexpected pass through the tail of the comet on February 3, 2007. Ulysses flew through McNaught's ion tail 160 million miles from the comet's core and instrument readings showed that there was "complex chemistry" in the region. The Solar Wind Ion Composition Spectrometer (SWICS) aboard Ulysses measured the composition speed of the comet tail and solar wind, and detected unexpected ions within the comet's tail and found that it had a major impact on the surrounding solar wind. It's the first time that researchers have detected O3+ oxygen ions (atoms of oxygen with a positive charge because they have five electrons instead of eight) near a comet. This suggested that the solar wind ions, originally missing most of their electrons, picked up some of their missing electrons as they passed through McNaught's atmosphere.

Besides that, SWICS found that even at 160 million miles from the comet's nucleus, the tail had slowed the solar wind to half its normal speed. The solar wind should usually be about 435 miles per second at that distance from the Sun, but inside the comet's ion tail, it was less than 249 miles per second.
"This was very surprising to me. Way past the orbit of Mars, the solar wind felt the disturbance of this little comet. It will be a serious challenge for us theoreticians and computer modellers to figure out the physics," —space science professor, Michael Combi.>>

http://en.wikipedia.org/wiki/X/1106_C1 wrote:
<<The Great Comet of 1106 (X/1106 C1), was a Great Comet that appeared on February 2, 1106, and was observed across the world from the beginning of February through to mid-March. It was recorded by astronomers in Wales, England, Japan, Korea, China and Europe. It was observed to split in two, and may have formed the Great Comet of 1882, Comet Ikeya-Seki and SOHO-620.
It is a member of the Kreutz Group, as Subfragment I, split from an earlier comet.
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A brief note in the Welsh manuscript known as the Brut y Tywysogion reads (in translation):

• [-1106]. In that year there was seen a star wonderful to behold, throwing out behind it a beam of light of the thickness of a pillar in size and of exceeding brightness, foreboding what would come to pass in the future: for Henry, emperor of Rome, after mighty victories and a most pious life in Christ, went to his rest. And his son, after winning the seat of the empire of Rome, was made emperor.

The 1106 annal of the Peterborough Chronicle describes the comet. The Dorothy Whitlock translation reads:

• In the first week of Lent, on the Friday, 16 February, in the evening, there appeared an unusual star, and for a long time after that it was seen shining a while every evening. This star appeared in the south-west; it seemed small and dark. The ray that shone from it, however, was very bright, and seemed to be like an immense beam shining north-east; and one evening it appeared as if this beam were forking into many rays toward the star from an opposite direction.>>

http://en.wikipedia.org/wiki/Kreutz_Sungrazers wrote:
<<The Kreutz Sungrazers are a family of sungrazing comets, characterized by orbits taking them extremely close to the Sun at perihelion. They are believed to be fragments of one large comet that broke up several centuries ago and are named for German astronomer Heinrich Kreutz, who first demonstrated that they were related. Several members of the Kreutz family have become Great Comets, occasionally visible near the Sun in the daytime sky. The most recent of these was Comet Ikeya-Seki in 1965, which may have been one of the brightest comets in the last millennium. Many hundreds of smaller members of the family, some only a few meters across, have been discovered since the launch of the SOHO satellite in 1995. None of these smaller comets survived their perihelion passage.

There are also signs that another cluster of bright Kreutz system comets is on its way to the Sun in future decades, with the earliest objects expected to arrive perhaps as soon as several years from now. During the next few decades, mankind should once again witness spectacular heavenly shows like that in 1965.

The first comet whose orbit had been found to take it extremely close to the Sun was the Great Comet of 1680. This comet was found to have passed just 200,000 km (0.0013 AU) above the sun's surface, equivalent to about half the distance between the Earth and the Moon. It thus became the first known sungrazing comet. Its perihelion distance was just 1.3 solar radii. Astronomers at the time, including Edmond Halley, speculated that this comet was a return of a bright comet seen close to the Sun in the sky in 1106. 163 years later, the Great Comet of 1843 appeared and also passed extremely close to the Sun. Despite orbital calculations showing that it had a period of several centuries, some astronomers wondered if it was a return of the 1680 comet. A bright comet seen in 1880 was found to be travelling on an almost identical orbit to that of 1843, as was the subsequent Great Comet of 1882. Some astronomers suggested that perhaps they were all one comet, whose orbital period was somehow being drastically shortened at each perihelion passage, perhaps by retardation by some dense material surrounding the Sun.

An alternative suggestion was that the comets were all fragments of an earlier sun-grazing comet. This idea was first proposed in 1880, and its plausibility was amply demonstrated when the Great Comet of 1882 broke up into several fragments after its perihelion passage. In 1888, Heinrich Kreutz published a paper showing that the comets of 1843—C/1843 D1 (Great March comet), 1880—C/1880 C1 (Great southern comet) and 1882—C/1882 R1 (Great September comet) were probably fragments of a giant comet that had broken up several revolutions before. The comet of 1680 proved to be unrelated to this family of comets.

After another Kreutz Sungrazer was seen in 1887 (C/1887 B1—Great southern comet), the next one did not appear until 1945. Two further sungrazers appeared in the 1960s, Comet Pereyra in 1963 and Comet Ikeya-Seki, which became extremely bright in 1965, and broke into three pieces after its perihelion. The appearance of two Kreutz Sungrazers in quick succession inspired further study of the dynamics of the group.
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A study by Brian Marsden in 1967 was the first attempt to trace back the orbital history of the group to identify the progenitor comet. All known members of the group up until 1965 had almost identical orbital inclinations at about 144°, as well as very similar values for the longitude of perihelion at 280–282°, with a couple of outlying points probably due to uncertain orbital calculations. A greater range of values existed for the argument of perihelion and longitude of the ascending node.

Marsden found that the Kreutz Sungrazers could be split into two groups, with slightly different orbital elements, implying that the family resulted from fragmentations at more than one perihelion. Tracing back the orbits of Ikeya-Seki and the Great Comet of 1882, Marsden found that at their previous perihelion passage, the difference between their orbital elements was of the same order of magnitude as the difference between the elements of the fragments of Ikeya-Seki after it broke up. This meant it was realistic to presume that they were two parts of the same comet which had broken up one orbit ago. By far the best candidate for the progenitor comet was that seen in 1106 (Great Comet of 1106): Ikeya-Seki's derived orbital period gave a previous perihelion almost exactly at the right time, and while the Great Comet of 1882's derived orbit implied a previous perihelion a few decades later, it would only require a small error in the orbital elements to bring it into agreement. The sungrazering comets of 1668, 1689, 1702 and 1945 seem to be closely related to those of 1882 and 1965, although their orbits are not well enough determined to establish whether they broke off from the parent comet in 1106, or the previous perihelion passage before that, some time in the 3–5th centuries AD. This subgroup of comets is known as Subgroup II.

http://upload.wikimedia.org/wikipedia/c ... chy_en.svg

The sungrazering comets observed in 1843 (Great Comet of 1843) and 1963 (Comet Pereyra) seem to be closely related and belong to the subgroup I, although when their orbits are traced back to one previous perihelion, the differences between the orbital elements are still rather large, probably implying that they broke apart from each other one revolution before that. They may not be related to the comet of 1106, but rather a comet that returned about 50 years before that. Subgroup I also includes comets seen in 1695, 1880 (Great Southern Comet of 1880) and in 1887 (Great Southern Comet of 1987), as well as the vast majority of comets detected by SOHO mission.

The distinction between the two sub-groups is thought to imply that they result from two separate parent comets, which themselves were once part of a 'grandparent' comet which fragmented several orbits previously. One possible candidate for the grandparent is a comet observed by Aristotle and Ephorus in 371 BC. Ephorus claimed to have seen this comet break into two. However modern astronomers are skeptical of the claims of Ephorus, because they were not confirmed by other sources. Instead comets that arrived between 3-th and 5-th centuries AD (comets of 214, 426 and 467) are considered as possible progenerators of the Kreutz family. The original comet must certainly have been very large indeed, perhaps as large as 100 km across (for comparison, the nucleus of Comet Hale-Bopp was about 40 km across).

Although its orbit is rather different from those of the main two groups, it is possible that the comet of 1680 is also related to the Kreutz Sungrazers via a fragmentation many orbits ago.

The Kreutz Sungrazers are probably not a unique phenomenon. Studies have shown that for comets with high orbital inclinations and perihelion distances of less than about 2 AU, the cumulative effect of gravitational perturbations tends to result in sungrazing orbits. One study has estimated that Comet Hale-Bopp has about a 15% chance of eventually becoming a sun-grazing comet.

Until recently, it would have been possible for even a very bright member of the Kreutz Sungrazers to pass through the inner solar system unnoticed, if its perihelion occurred between about May and August. At this time of year, as seen from Earth, the comet would approach and recede almost directly behind the sun, and could only become visible extremely close to the sun if it became very bright. Only a remarkable coincidence between the perihelion passage of the Eclipse Comet of 1882 and a total solar eclipse allowed its discovery.>>