| |
|
|
Comets-Comet_Hartley_2-NASA-2.jpgComet "Hartley 2" (Close-up and Dimensions)110 visitenessun commentoMareKromium
|
|
Comets-Comet_Holmes-0.jpgA "Light Arrow" is heading towards "Heart & Soul"...75 visiteCaption NASA:"Two spectacular comets graced Earth's skies during 2007.
Both comets became bright enough to be seen by the unaided eye of the casual sky enthusiast. Early in 2007, Comet McNaught grew brighter than any comet in 40 years, displaying a beautiful dust tail that flowed across the sky.
Comet McNaught (a.k.a. c/2006 P1) became known as the "Great Comet" of 2007, sported unusual striations in its expansive dust tail, and showed unexpectedly complex chemistry in its ion tail.
Toward the year's end, normally docile and faint Comet Holmes brightened suddenly and unexpectedly to naked eye visibility. Remarkably, Comet 17P/Holmes stayed bright for weeks even though it lies beyond the orbit of Mars.
No distant comet in recent history has remained so bright for so long.
In this view, a white Comet Holmes was photographed in early December posing with the Heart and Soul Nebulae".MareKromium
|
|
Comets-Comet_Holmes-TView.jpgTelescopic View of the Comet Holmes66 visiteCaption NASA, da "NASA - Picture of the Day" del 29 Ottobre 2007:"What's happened to Comet Holmes? A normally docile comet discovered over 100 years ago, Comet 17P/Holmes suddenly became nearly one million times brighter last week, possibly over just a few hours. In astronomical terms, the comet brightened from magnitude 17, only visible through a good telescope, to magnitude 3, becoming visible with the unaided eye. Comet Holmes had already passed its closest to the Sun in 2007 May outside the orbit of Mars and was heading back out near Jupiter's orbit when the outburst occurred. The comet's sudden brightening is likely due to some sort of sunlight-reflecting outgassing event, possibly related to ice melting over a gas-filled cavern, or possibly even a partial breakup of the comet's nucleus. Pictured above through a small telescope, Comet Holmes appeared as a fuzzy yellow spot, significantly larger in angular size than Earth-atmosphere blurred distant stars. Although Comet Holmes' orbit will place it in northern hemisphere skies for the next two years, whether it will best be viewed through a telescope or sunglasses remains unknown".MareKromium
|
|
Comets-Comet_Holmes-TW-P17HolmesWeb3_goldman.jpgComet 17-P-Holmes and its Golden Coma74 visiteCaption NASA, da "NASA - Picture of the Day", del 3 Novembre 2007:"Surprising Comet Holmes remains easily visible as a round, fuzzy cloud in the Northern constellation Perseus. Skywatchers with telescopes, binoculars, or those that just decide to look up can enjoy the Solar System's latest prodigy as it glides about 150 MKM from Earth, beyond the orbit of Mars.
Still expanding, Holmes now appears to be about 1/3 the size of the Full Moon, and many observers report a yellowish tint to the dusty coma. A golden color does dominate this telescopic view recorded on November 1, showing variations across the coma's bright central region.
But where's the comet's tail? Like any good comet, Holmes' tail would tend to point away from the Sun. That direction is nearly along our line-of-sight behind the comet, making its tail very difficult to see". MareKromium
|
|
Comets-Comet_Holmes-UV.gifComet 17-P-Holmes73 visiteCaption NASA, da "NASA - Picture of the Day" del 30 Ottobre 2007:"Go outside tonight and see Comet Holmes.
No binoculars or telescopes are needed -- just curiosity and a sky map.
Last week, Comet 17P/Holmes underwent an unusual outburst that vaulted it unexpectedly from obscurity into one of the brightest comets in recent years.
Sky enthusiasts from the Northern Hemisphere have been following the comet's progress closely. Pictured above Quebec, Canada, the coma of Comet Holmes has been noticeably expanding over the past few days. In the above picture, an image of Jupiter has been placed artificially nearby to allow for a comparison of angular sizes.
Jupiter has been scaled to the size it would appear at the current location of Comet Holmes. How Comet Holmes will further evolve is unknown, with one possibility being that the expanding gas cloud that started from its recent outburst will slowly disperse and fade".MareKromium
|
|
Comets-Comet_Holmes-UW.jpgComet 17-P-Holmes is getting Bigger!73 visiteCaption NASA, da "NASA - Picture of the Day", del 5 Novembre 2007:"Comet Holmes continues to be an impressive sight to the unaided eye. The comet has diminished in brightness only slightly, and now clearly appears to have a larger angular extent than stars and planets.
Astrophotographers have also noted a distinctly green appearance to the comet's coma over the past week.
Pictured above over Spain in 3 digitally combined exposures, Comet 17P/Holmes now clearly sports a tail. The blue ion tail is created by the solar wind impacting ions in the coma of Comet Holmes and pushing them away from the Sun. Comet Holmes underwent an unexpected and dramatic increase in brightness starting only two weeks ago. The detail visible in Comet Holmes' tail indicates that the explosion of dust and gas that created this dramatic brightness increase is in an ongoing and complex event.
Comet Holmes will move only slightly on the sky over the next month (such as December 2007)".MareKromium
|
|
Comets-Comet_Holmes-UX.jpgComet 17-P-Holmes and its - now - Green Coma75 visiteCaption NASA:"This gorgeous skyscape spans some 10° across the Constellation of Perseus, about the size of a generous binocular field of view.
The deep exposure includes bright stars, emission nebulae, star clusters, and, of course, the famous Comet Holmes.
The brightest star in view, Alpha Persei, is itself surrounded by a loose cluster of stars - the Alpha Per Moving Cluster - at a distance of about 600 LY.
But, at a distance of a mere 14 Light-Minutes (LM), bright Comet 17-P-Holmes still dominates the scene with its fluorescing greenish coma and foreshortened blue tail".MareKromium
|
|
Comets-Comet_Holmes-UY.jpgComet 17-P-Holmes, from Hungary70 visiteCaption NASA:"A beautiful blue ion tail has become visible in deep telescopic images of Comet Holmes. Pointing generally away from the Sun and also planet Earth, the comet's ion tail is seriously foreshortened by our extreme viewing angle.
Still, enthusiastic comet watchers have remarked that on the whole, the compact but tentacled appearance suggests a jellyfish or even a "cosmic calamaro".
This stunning view of the comet's greenish coma and blue tail was recorded on November 4, 2007, in clear skies near Budapest, Hungary.
The colors are caused by molecules in the tenuous gas, like C2 (green) and CO+ (blue), fluorescing in sunlight". MareKromium
|
|
Comets-Comet_Holmes-UZ-0.jpgComet 17-P-Holmes, from HST64 visiteCaption NASA:"These images taken by NASA's Hubble Space Telescope reveal Comet Holmes's bright core. The images show that the coma, the cloud of dust and gas encircling the comet, is getting fainter over time. The coma was brightest in the Oct. 29 image. It is two times fainter on Oct. 31 and nine times dimmer on Nov. 4 than during the Oct. 29 observation.
The coma is getting fainter because it is expanding. A huge number of small dust particles was created during the Oct. 23 outburst. Since then those particles have been moving away from the nucleus and filling interplanetary space.
The coma therefore is becoming more diffuse over time.
The nucleus, however, is still active and is producing a significant amount of new dust. So the region around the nucleus is still much brighter (at least 10 times brighter) than it usually is at this point in the comet's orbit.MareKromium
|
|
Comets-Comet_Holmes-UZ-1.gifBigger than the Sun!66 visiteCaption NASA:"The spherical coma of Comet Holmes has swollen to a diameter of over 1,4 MKM, making the tenuous, dusty cloud even bigger than the Sun. Scattering sunlight, all that dust and gas came from the comet's remarkably active nucleus, whose diameter before the late October outburst was estimated to be a mere 3,4 Km.
In this sharp image, recorded on November 14, 2007, with the Canada-France-Hawaii Telescope, stars are easily visible right through the outer coma, while the nucleus is buried inside the condensed, bright region. The bright region of the coma seems offset from the center, consistent with the idea that a large fragment drifted away from the nucleus and disintegrated, producing the comet's spectacular outburst. Of course, more recent images of Holmes also show the bright star Mirfak (Alpha Persei) shining through as the comet sweeps slowly through the constellation Perseus".MareKromium
|
|
Comets-Comet_Holmes-UZ-1.jpgComet 17-P-Holmes, from Earth and from HST77 visiteNASA's HST has probed the bright core of Comet 17P/Holmes, which, to the delight of sky watchers, mysteriously brightened by nearly a millionfold in a 24-hour period beginning Oct. 23, 2007.
Astronomers used Hubble's powerful resolution to study Comet Holmes' core for clues about how the comet brightened. The orbiting observatory's Wide Field Planetary Camera 2 (WFPC2) monitored the comet for several days, snapping images on Oct. 29, Oct. 31, and Nov. 4. Hubble's crisp "eye" can see objects as small as 33 miles (54 Km) across, providing the sharpest view yet of the source of the spectacular brightening.
The Hubble image at right, taken Nov. 4, shows the heart of the comet. The central portion of the image has been specially processed to highlight variations in the dust distribution near the nucleus. About twice as much dust lies along the east-west direction (the horizontal direction) as along the north-south direction (the vertical direction), giving the comet a "bow tie" appearance.
The composite color image at left, taken Nov. 1 by an amateur astronomer, shows the complex structure of the entire coma, consisting of concentric shells of dust and a faint tail emanating from the comet's right side.
The nucleus-the small solid body that is the ultimate source of all the comet's activity- is still swaddled in bright dust, even 12 days after the spectacular outburst. "Most of what Hubble sees is sunlight scattered from microscopic particles," explained Hal Weaver of The Johns Hopkins University Applied Physics Laboratory in Laurel, Md., who led the Hubble investigation. "But we may finally be starting to detect the emergence of the nucleus itself in this final Hubble image."
Hubble first observed Comet 17P/Holmes on June 15, 1999, when there was virtually no dusty shroud around the nucleus. Although Hubble cannot resolve the nucleus, astronomers inferred its size by measuring its brightness. Astronomers deduced that the nucleus' diameter was approximately 2.1 miles (3.4 kilometers), about the length of New York City's Central Park. They hope to use the new Hubble images to determine the size of the comet's nucleus to see how much of it was blasted away during the outburst.
Hubble's two earlier snapshots of Comet Holmes also showed some interesting features. On Oct. 29, the telescope spied three "spurs" of dust emanating from the nucleus, while the Hubble images taken on Oct. 31 revealed an outburst of dust just west of the nucleus.
The Hubble images, however, do not show any large fragments near the nucleus of Comet Holmes, unlike the case of Comet 73P/Schwassmann-Wachmann 3 (SW3). In the spring of 2006 Hubble observations revealed a multitude of "mini-comets" ejected by SW3 after the comet increased dramatically in brightness.
Ground-based images of Comet Holmes show a large, spherically symmetrical cloud of dust that is offset from the nucleus, suggesting that a large fragment broke off and subsequently disintegrated into tiny dust particles after moving away from the main nucleus.
Unfortunately, the huge amount of dust near the comet's nucleus and the comet's relatively large distance from Earth (149 million miles, or 1.6 astronomical units, for Holmes versus 9 million, or 0.1 astronomical unit for SW3), make detecting fragments near Holmes nearly impossible right now, unless the fragments are nearly as large as the nucleus itself.
The Hubble Comet Holmes observing team comprises H. Weaver and C. Lisse (The Johns Hopkins University Applied Physics Laboratory); P. Lamy (Laboratoire d'Astrophysique de Marseille, France); I. Toth (Konkoly Observatory, Hungary); M. Mutchler (Space Telescope Science Institute); W. Reach (California Institute of Technology); and J. Vaubaillon (California Institute of Technology).
MareKromium
|
|
Comets-Comet_Holmes-UZ-2.jpgComet 17-P-Holmes, from Hungary65 visiteCaption NASA:"Comet Holmes refuses to fade. The unusual comet that surprisingly brightened nearly a million-fold in late October continues to remain visible to the unaided eye from dark locations. Night to night, Comet 17P/Holmes is slowly gliding through the constellation Perseus, remaining visible to northern observers during much of the night right from sunset. Pictured above, Comet Holmes was captured from Hungary last week. The remarkable snowball continues to retain a huge coma, but now shows very little of a tail. To the far right is the open cluster of stars NGC 1245.
How much longer Comet Holmes will remain visible to the unaided eye is unknown".MareKromium
|
|
| 288 immagini su 24 pagina(e) |
|
|
|
|
6 | |
|
|
|
|
|
|
|
