Le polveri cometarie della PanStarrs...

Complimenti a Lorenzo Comolli, autore della foto (da APOD)

The Broad Tail of PanSTARRS

Image Credit & Copyright: Lorenzo Comolli - Model Overlay: Marco Fulle (INAF)

Explanation: For northern hemisphere skygazers, fading Comet PanSTARRS (C/2011 L4) still hangs above the western horzion, after sunset but before moonrise in the coming days. Its perspective from planet Earth continues to reveal the comet's broad dust tail. This long exposure tracking the comet, made on March 21, has been enhanced to show remarkable, subtle striations in PanSTARRS' tail. Place your cursor over the image (or click here) to show an overlay of the dust tail with a model network of synchrones and syndynes. Synchrones (long dashed lines) trace the location of dust grains released from the comet nucleus at the same time and with zero velocity. The successive synchrone lines shown are separated by 1 day and start at the bottom, 10 days before the comet's March 10 perihelion passage. Syndynes (solid lines) show the location of dust grains of the same size, also released with zero velocity. Dust grains 1 micron wide lie along the upper syndyne. The grain width increases counterclockwise to 500 micron wide grains along the syndyne nearly parallel to the comet's orbit (short dashed line through the nucleus location). In the model, forces acting on the dust grains were assumed to be gravity and the pressure of sunlight. The periodic striations in PanSTARRS' tail seem to closely follow the model synchrone lines.

Canarie: la cometa PanStarrs, le nuvole e la falce di Luna

L'Osservatorio di La Plama (Canarie) con la prima apparizione di martedì della cometa PanStarrs accanto alla falce di Luna crescente... Astronomy Picture of the Day.

Clouds, Comet and Crescent Moon

Image Credit & Copyright: Babak Tafreshi (TWAN)

Explanation: In silhouette against the colorful evening twilight glow, clouds part in this much anticipated magic moment. The scene captures naked-eye Comet PanSTARRS peeking into northern hemisphere skies on March 12. The comet stands over the western horizon after sunset, joined by the thin, flattened crescent of a day old Moon. Posing for its own beauty shot, the subtly lit dome of the 4.2 meter William Herschel Telescope is perched above cloud banks on the Canary Island of La Palma. While PanSTARRS has not quite developed into the spectacular comet once hoped for, it is still growing easier to see in the north. In coming days it will steadily climb north, farther from the Sun into darker western evening skies.

Spettacolo: le due comete di marzo nel cielo americano...

Comets Lemmon and PanSTARRS Peaking

Image Credit & Copyright: Yuri Beletsky (ESO)

Explanation: Two impressive comets will both reach their peak brightness during the next two weeks. Taking advantage of a rare imaging opportunity, both of these comets were captured in the sky together last week over the Atacama desert in South America. Comet C/2012 F6 (Lemmon), visible on the upper left of the above image, is sporting a long tail dominated by glowing green ions. Comet C/2011 L4 (PanSTARRS), visible near the horizon on the lower right, is showing a bright tail dominated by dust reflecting sunlight. The tails of both comets point approximately toward the recently set Sun. Comet Lemmon will be just barely visible to the unaided eye before sunset in southern skies for the next week, and then best viewed with binoculars as it fades and moves slowly north. Comet PanSTARRS, however, will remain visible in southern skies for only a few more days, after which it will remain bright enough to be locatable with the unaided eye as it moves into northern skies. To find the giant melting snowball PanSTARRS, sky enthusiasts should look toward the western horizon just after sunset. Deep sky observers are also monitoring the brightening of Comet C/2012 S1 (ISON), which may become one of the brightest objects in the entire night sky toward the end of 2013.