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RECORD-SETTING ASTEROID FLYBY: On Feb. 15th an asteroid about half the size of a football field will fly past Earth closer than many man-made satellites. Since regular sky surveys began in the 1990s, astronomers have never seen an object so big come so close to our planet. [full story] [video]
RARE ICE HALOS: On January 28th at the Vitosha mountain in Sofia, Bulgaria, skiers stopped in their tracks when a magnificent network of luminous arcs and halos formed around the midday sun. Janeta Ganchevska pulled a mobile phone out of her jacket and snapped this photo of the apparition:
"Small, fine crystals were raining from the sky," says Ganchevska. "Sunlight shining through the crystals produced these very bright halos."
Atmospheric optics expert Les Cowley comments on the display: "Rare halo arcs come in clusters. They are a sign of large numbers of near perfect hexagonal ice crystals drifting in the air. In this case, the crystals were nearby and called 'diamond dust.'"
"Many rare arcs get called after their discoverers," says Cowley, who points out the named arcs in Ganchevska's picture: "First above the sun is a faint ‘V’, the mysterious Moilanen arc, named after the Finland halo expert. Next we have the well-known 22 degree halo and the gull-winged shaped tangent arc. Above that the rare Parry arc first recorded in the Arctic in 1820 by the famous explorer. Yet further up is a colourful and rare supralateral arc. Yet another picture shows two greater rarities, a Tape arc (Parry supralateral) named after halo expert Walter Tape and a helic arc."
"There are arcs waiting out there for a discoverer," says Cowley. "Get looking!"
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ERUPTING MAGNETIC FILAMENT: As expected, an unstable filament of magnetism curling over the sun's northeastern limb erupted yesterday. NASA's Solar Dynamics Observatory recorded the blast at approximately 0515 UT on Jan. 31st:
Despite the obvious energy of the blast, very little of the filament actually flew into space. The sun's gravity pulled most of the debris back to the stellar surface. So this eruption was primarily photogenic, not geoeffective.
Elsewhere on the sun, no sunspots are actively flaring. NOAA forecasters estimate a slim 1% chance of M-class or X-class solar flares during the next 24 hours. Solar flare alerts: text, voice.
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GREEN COMET LEMMON: 2013 could be the Year of the Comet. Comet Pan-STARRS is set to become a naked eye object in March, followed by possibly-Great Comet ISON in November. Now we must add to that list green Comet Lemmon (C/2012 F6). "Comet Lemmon is putting on a great show for us down in the southern hemisphere," reports John Drummond, who sends this picture from Gisborne, New Zealand:
"I took the picture on Jan. 23rd using a 41 cm (16 in) Meade reflector," says Drummond. "It is a stack of twenty 1 minute exposures." That much time was required for a good view of the comet's approximately 7th-magnitude coma ("coma"=cloud of gas surrounding the comet's nucleus).
Lemmon's green color comes from the gases that make up its coma. Jets spewing from the comet's nucleus contain cyanogen (CN: a poisonous gas found in many comets) and diatomic carbon (C2). Both substances glow green when illuminated by sunlight in the near-vacuum of space.
Discovered on March 23rd 2012 by the Mount Lemmon survey in Arizona, Comet Lemmon is on an elliptical orbit with a period of almost 11,000 years. This is its first visit to the inner solar system in a very long time. The comet is brightening as it approaches the sun; light curves suggest that it will reach 2nd or 3rd magnitude, similar to the stars in the Big Dipper, in late March when it approaches the sun at about the same distance as Venus (0.7 AU). Northern hemisphere observers will get their first good look at the comet in early April; until then it is a target exclusively for astronomers in the southern hemisphere.
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