Geminids (GEM): 7 Δεκ. ως 17 Δεκ. Μέγιστο: 14 Δεκ. 2009

Bi2L · Δεκέμβριος 7, 2009

Geminids (GEM) 2009

πηγη imo.net

http://www.imo.net/calendar/2009#gem

Active: December 7-17
Maximum: December 14 5h10m UT (λo = 262°2) 2.3h
ZHR = 120
Radiant: α = 112° δ = +33°
Radiant drift: see Table 6
v∞ = 35 km/s; r = 2.6
TFC: α = 087° δ = +20° and
α = 135° δ = +49° before 23h local time
α = 087° δ = +20° and α = 129° δ = +20° after 23h local time (β > 40° N)
α = 120° δ = -03° and α = 084° δ = +10° (β < 40° N)
IFC: α = 150° δ = +20° and α = 060° δ = +40° (β > 20° N)
α = 135° δ = -05° and α = 080° δ = 00° (β < 20° N)

One of the finest, and probably the most reliable, of the major annual showers presently observable, whose peak this year is virtually coincident with new Moon. The Geminid radiant culminates around 2h local time, but well north of the equator it rises about sunset, and is at a usable elevation from the local evening hours onwards, while in the southern hemisphere, the radiant appears only around local midnight or so. Even from more southerly sites, this is a splendid shower of often bright, medium-speed meteors, a rewarding sight for all watchers, whatever method they employ. The peak has shown slight signs of variability in its rates and timing in recent years, with the more reliably-observed maxima during the past two decades all having occurred within 2h20m of the time given above. The main predicted timing favours places from all across the Americas eastwards to western Europe and western Africa. An earlier or later timing would extend this best-visible zone some way eastwards or westwards respectively. Some mass-sorting within the stream means the fainter telescopic meteors should be most abundant almost 1° of solar longitude (about one day) ahead of the visual maximum, with telescopic results indicating such meteors radiate from an elongated region, perhaps with three sub-centres. Further results on this topic would be useful.

http://www.imo.net/node/1256

πηγη popastro.com

http://www.popastro.com/sections/meteor/meteor-dec2009.htm

Shower of the Month: The Geminids

IYA2009's last major shower, the Geminids (GEM), have a moonless maximum expected on December 14 around 05h UT. New Moon is on December 16. The Geminid radiant, shown on the chart here, rises around sunset and reaches a usefully-observable elevation for meteor watchers by about 20h UT from Britain. After this, it remains well-placed for the rest of the night, culminating around 02h. Highest Zenithal Hourly Rates (ZHRs) should be circa 120 judging by recent returns, and observed rates from the UK on December 13-14 under clear, very dark skies could be a meteor a minute or more throughout the post-midnight hours, if its activity is of this strength again. This is because Geminid rates often remain close to their maximum levels for 6 to 10 hours to either side of their best, and activity is normally good, if lower, for a night or two before, and sometimes a night after, the maximum in an average year. Thus pleasing shower rates may be glimpsed then, even if clouds intervene on the peak night. Geminids are medium speed and often bright meteors, though few leave glowing persistent trains after them. Much lower Geminid rates may be seen away from the maximum in any moonless skies available between December 7 to 17, from past years' activity. Information from the International Meteor Organization's (IMO's) Video Commission suggested Geminid video rates had been detected at times from November 30 to December 18 during the last decade, but a fresh re-evaluation of this found instead a detectable video rate was apparent chiefly from December 4 to 16. This could indicate some visual Geminids may be apparent a few days earlier than expected, albeit December's first full Moon on the 2nd will prevent any dark-sky checking then this year. Although the shower's parent object, Apollo asteroid 3200 Phaethon (possibly a dormant or extinct comet) passed closest to Earth since its 1983 discovery on 2007 December 10, it seemed not to have affected Geminid rates then (it was not anticipated it would), nor is it expected to this year.

πηγη meteorshowersonline.com

http://meteorshowersonline.com/geminids.html

Major Activity:
Recommended experience level: Beginning and up

Observing the Geminids
This is one of the best meteor showers of the year and never seems to disappoint observers.

This meteor shower gets the name "Geminids" because it appears to radiate from the constellation Gemini. An observer in the Northern Hemisphere can start seeing Geminid meteors as early as December 6, when one meteor every hour or so could be visible. During the next week, rates increase until a peak of 50-80 meteors per hour is attained on the night of December 13/14. The last Geminids are seen on December 18, when an observer might see a rate of one every hour or so.

For observers in the Southern Hemisphere, the Geminid radiant never climbs far above the horizon, and this considerably reduces the number of Geminid meteors you are likely to see. Nevertheless, on the night of maximum, it is possible to see 20 meteors per hour coming up from the northern horizon.

There are other, weaker meteor showers going on around the same time as the Geminids, but the best way to know if the meteor you see is a Geminid is to mentally trace the meteor backwards. If you end up at Gemini then you have probably seen a Geminid meteor! If you are not sure where Gemini is in the sky, the following charts will help you find it from both the Northern Hemisphere and Southern Hemisphere:

Location of the Geminids

For Northern Hemisphere Observers

History

The appearance of this meteor shower seems to have been fairly sudden during the 1860s. It was first noted in 1862, when R. P. Greg (Manchester, England) found a radiant in the constellation Gemini for the period of December 10-12. B. V. Marsh and A. C. Twining (United States) independently discovered the activity around the same time. A. S. Herschel noted meteors emanating from Gemini during December 12/13, 1863, as well as three fireballs from near the same radiant in 1863 and 1864. During the 1870s, observations of the Geminids became more numerous as astronomers realized a new annual shower was active.

The first estimate of the strength of the Geminids came in 1877, when the hourly rate was given as about 14. The same rate was also given by observers in England during 1892, but it was noted that almost twice as many bright meteors were present than had been seen in 1877. In 1896, English observers gave hourly rates near 23 and also observed "a number of bright pale green meteors...."

The reported rates continued to increase through most of the 20th century. During the 1900s, the rates averaged about 20 per hour. The rates averaged near 50 per hour during the 1930s, 60 per hour during the 1940s and 1950s, 65 per hour during the 1960s, and 80 per hour during the 1970s. The rates stayed near 80 per hour during the remainder of that century.

Visual observations have shown this shower to exhibit a very sharp peak of activity, with hourly rates remaining above a value of half the maximum for about two days. Although visual evidence of this shower indicates activity persists from December 6 to 19, photography and radar studies have revealed apparent activity spanning the period of November 30 to December 29.

Papers studying the sizes of the Geminid meteors were published by G. H. Spalding in 1982 and P. B. Babadzhanov and Yu. V. Obrubov in 1984. Both revealed that the meteoroids within the stream were separated by size, so that particle size generally increases during the duration of the stream. Such an occurrence usually indicates the stream is very old.

A major advance in the understanding of this meteor stream was made in 1947. F. L. Whipple had been involved in the Harvard Meteor Project, a photographic survey aimed at better understanding meteors and their origins by obtaining data that could be used to calculate orbital elements. While analyzing meteors associated with the Geminids he found an orbital period of only 1.65 years, as well as a high eccentricity and a low inclination. Such an orbit attracted the attention of M. Plavec (Prague), who began investigating how the gravity of the planets changed the orbit.

Plavec found that only two planets affect the orbit of the Geminids---Earth and Jupiter, though the former was considered negligible compared to the effects of the giant planet. "From the observer's point of view," he wrote, "the most important phenomenon is the rapid backward shift of the [date of maximum]." The degree of this shift was calculated to cause the date of maximum to occur one day earlier every 60 years. Another interesting conclusion involved the point of intersection between the stream's orbit and the plane of Earth's orbit. For the year 1700, it was found that the intersection point was placed 0.1337 AU inside Earth's orbit. For 1900, the intersection point was located 0.0178 AU inside Earth's orbit and in 2100, the point would be 0.1066 AU outside of Earth's orbit. Thus, Plavec not only showed why the activity of the Geminids was steadily increasing, but he also demonstrated that the activity would eventually decline and that sometime in the future Earth would no longer contact the stream's orbit.

Plavec's work was essentially confirmed in 1982 by K. Fox, I. P. Williams, and D. W. Hughes; however, the observations did not reflect the predicted change in the date of maximum that amounted to one day in about 60 years. The authors theorized that the predicted change was actually being altered because of "the shape of the cross-section of the intersection of the meteor stream with the ecliptic plane." A computer simulation predicted the meteor rate profile was skew. Fox, Williams, and Hughes further elaborated on this distribution in a paper published in 1983. "At the present time the Geminid shower slowly builds up to maximum rate and then drops away from maximum relatively sharply. About 50 yr ago the skewness should have been exactly the opposite with a sharp build up to maximum rate and a much slower falling away." The proposed model indicated Earth's orbit would intersect the Geminid stream only between 1800 and 2100.

A major question concerning the Geminid stream involves its origin. It was long known that no parent comet for this stream was present in current catalogs, but, since the exact size and shape of the stream were not known until 1947, few conjectures were made. In 1950, Plavec theorized about the Geminid stream's parent body and pointed out that the "existence of a parent comet in such a short-period orbit, even in the past, seems to be not very probable. Planetary perturbations could scarcely have reduced the semimajor axis so much. More probably, the Geminids were separated from a parabolic comet by the close approach of the comet to the sun." Concerning a possible candidate for the parabolic comet mentioned, Plavec considered the great comet of 1680 (after a suggestion made in 1931 by Maltzev) and concluded that the close approach of the two orbits at a point slightly beyond the Geminid perihelion point, made a possible connection impossible to exclude.

L. Kresak strengthened the comet link to this meteor stream's formation, but instead of offering a theory as exotic as Plavec's, he favored a more direct formation of the Geminids. In 1972, he wrote that the parent comet "must have previously occupied the present orbit." He stressed that the compact nature of the stream would eliminate the possibility of it having formed in a different orbit and then been perturbed into the present orbit. Eleven years later, Kresak's theory would gain considerable strength.

On October 11, 1983, during a search for moving objects amidst the data gathered by the Infrared Astronomical Satellite (IRAS), S. Green and J. K. Davies found a rapidly moving asteroid in Draco. The next evening, C. Kowal (Palomar Observatory, California, USA) confirmed the body by photographing it with the 48-inch Schmidt telescope. The asteroid received the preliminary designation 1983 TB. As early orbital calculations were being made, the International Astronomical Union Circular for October 25, 1983, relayed the opinion of Whipple that this asteroid moved in an orbit almost identical to that of the Geminid meteor stream. Additional observations confirmed the link and the asteroid eventually received the permanent designation of 3200 Phaethon. The excitement of having found the parent body of the Geminid stream was almost dwarfed by another realization, this was the first time an asteroid had been definitely linked to a meteor shower and it subsequently serves as an important link between comets and meteor streams.

vtsamis · Δεκέμβριος 11, 2009

Λέτε να μας κάνει το χατήρι ο καιρός; ... και χωρίς φεγγάρι;

Bi2L · Δεκέμβριος 11, 2009

Βαγγελη...αυτο ελπιζω κι εγω...εαν ουρανο σαν τον σημερινο (εχουμε μια πολυ ομορφη λιακαδα σημερα ), και εφοσον οι Διδυμοι ανεβαινουν νωρις θα εχουμε οοοολο το βραδυ μπροστα μας να τους βλεπουμε να πεφτουν ...σε αντιθεση με τους Λεοντίδες οπου επρεπε να περιμενουμε τα μεσανυχτα για να τους δουμε. Βεβαια το μεγιστο θα ειναι νωρις το πρωι 7:10...αλλα τι να κανουμε

Παντως στο Imo.net εχουμε ιδη τα πρωτα στατιστικα

http://www.imo.net/live/geminids2009/

Εδω: http://www.imo.net/visual/report/electronic

οποιος εχει κανει καταγραφη διαττοντων μπορει να ανεβασει το δεδομενα του.

Bi2L · Δεκέμβριος 14, 2009

Δυστυχως ο καιρος μας τα εχει κανει ολα μουσκεμα εδω

Παντως με βαση το σχεδιαγραμα στο ιμο....βλεπω οτι υπαρχει αρκετη δραστηριοτητα, κριμα που δεν μπορουμε να δουμε κι εμεις κατι...

http://www.imo.net/live/geminids2009/

vtsamis · Δεκέμβριος 14, 2009

Βασίλη, κι εδώ στην Αθήνα τα ίδια... συνεχής νεφοκάλυψη και κάποια ψιλόβροχα. Στις 4 κάπως έδειχνε να ανοίγει αλλά ξανάκλεισε. Το ίδιο και στις 5:30.

Πάντως οι φίλοι μας οι Ιρλανδοί είχαν ρέντα. Έχασαν τη μπάλα στο μέτρημα Διδυμείδων... Ο Frank περιγράφει την καλύτερη βροχή που έχει ζήσει:

http://www.irishastronomy.org/cms/forum?func=view&catid=42&id=82546&limit=15&start=15#82592

Μήπως να το καθιερώσουμε εμείς να πηγαίνουμε το χειμώνα στην Ιρλανδία για παρατήρηση κι αυτοί να έρχονται το καλοκαίρι στον Πάρνωνα; Έχει κανείς ... αντίρηση;

Φιλικά,

Βαγγέλης

Bi2L · Δεκέμβριος 15, 2009

Βασίλη, κι εδώ στην Αθήνα τα ίδια... συνεχής νεφοκάλυψη και κάποια ψιλόβροχα. Στις 4 κάπως έδειχνε να ανοίγει αλλά ξανάκλεισε. Το ίδιο και στις 5:30.
Πάντως οι φίλοι μας οι Ιρλανδοί είχαν ρέντα. Έχασαν τη μπάλα στο μέτρημα Διδυμείδων... Ο Frank περιγράφει την καλύτερη βροχή που έχει ζήσει:
http://www.irishastronomy.org/cms/forum?func=view&catid=42&id=82546&limit=15&start=15#82592
Μήπως να το καθιερώσουμε εμείς να πηγαίνουμε το χειμώνα στην Ιρλανδία για παρατήρηση κι αυτοί να έρχονται το καλοκαίρι στον Πάρνωνα; Έχει κανείς ... αντίρηση;

Φιλικά,
Βαγγέλης

Καλα....οι Ιρλανδοι πρεπει να επαθαν την πλακα τους!!!! Θελω κι'γω