Swooning For The Moon And Comet Catalina

Delicate crescent and earthshine this morning (Dec. 9) at dawn. Credit: Bob King
A delicate crescent moon filled with earthshine this morning (Dec. 9) at dawn. Credit: Bob King

The moon’s been killer beautiful the past couple mornings. As the waning crescent has grown ever slender, the earthshine has become ever more amazing. Earthshine is the faint illumination filling out the remainder of the lunar disk caused by sunlight reflected from the Earth to the moon and back. I hate to see the crescent go — new moon is Friday — but with its departure, skies are now dark before dawn, perfect for viewing Comet Catalina.

Comet C/2013 US10 Catalina this morning (Dec. 10) photographed with a 200mm lens (f/2.8, ISO 800) on a tracking mount. The dust tail that I saw in binoculars point below the pale blue coma; the gas tail points the other way to the northwest. Credit: Bob King
Comet C/2013 US10 Catalina this morning (Dec. 9) photographed with a 200mm lens (f/2.8, ISO 800) on a tracking mount. The dust tail that I saw in binoculars extends below the pale greenish coma; the gas tail points the other way to the northwest. The bright star is Iota Virginis.  Credit: Bob King

Using 10×50 binoculars this morning, I easily spotted the comet a few degrees to the left and above Venus. How nice that it’s finally high enough in the sky I needn’t drive five miles to find an open horizon. The joys of stargazing from the front porch! Catalina looked like a small fuzzball with an obvious bright center.  When it reached its highest altitude at the start of morning twilight, I could make out the faint streak of a dust tail sticking out below (southeast) of the comet’s head with maybe a hint of gas tail. Despite my best efforts using eyes alone, I was unable to see any trace of Catalina at its current magnitude  of +6.5.

Blazing Venus and the comet (upper left) were just under 5°apart this morning. Credit: Bob King
Blazing Venus and the comet (green dot at upper left) were just under 5 degrees apart this morning. You can use Venus (see below) to help point you to the comet. Credit: Bob King

Through the telescope, the view resembled the photo above with a bright, dense aqua-hued coma and tails that extended out either side like bicycle handlebars. The dust tail appeared brighter overall, but the blue gas tail seemed to go on and on – maybe for as much as two full degrees. At the very center of the coma I could make out a faint “false nucleus”, the name given to the feature at a comet’s center that looks almost but not quite like a point. The real nucleus, far too small to see, spins and spews the ingredients for tail-making within this minute compaction.

A thicker crescent caught up in thin clouds on Tuesday morning, Dec. 8th. You can see the start of a lunar corona below the crescent. Credit: Bob King
A thicker crescent caught up in thin clouds on Tuesday morning, Dec. 8th. You can see the start of a lunar corona below the crescent. Credit: Bob King

I encourage anyone with a pair of binoculars to step outside and look for Comet Catalina the next clear dawn. Go out 2  hours before sunrise — that’ll give you a half hour to find and view the comet before twilight begins. You can use this new map to help you find it.

This map shows Comet Catalina's daily positions in relation to Venus through Dec. 22nd around 6 a.m. CST. Keep in mind Venus doesn't sit still but will slowly move in the direction of the arrow, separating from the comet. Stars are shown to magnitude +6.5 with the brighter ones labeled. Source: Chris Marriott's SkyMap
You can use Venus for the next week or so to help you find Comet Catalina as it tracks across the constellation Virgo. This map shows the comet’s daily position relative to Venus around 6 a.m. CST through Dec. 22nd. Keep in mind that Venus doesn’t sit still but will slowly move in the direction of the arrow, separating from the comet. Stars are shown to magnitude +6.5 with the brighter ones labeled. Source: Chris Marriott’s SkyMap

 

2 Responses

    1. astrobob

      Hi Joe,
      Last quarter moon (a half moon) happens 7 days before new, so the waning crescent lasts for 6 days, becoming thinner with each day.

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