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BAA electronic bulletin
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The evening elongation of Venus, 2017
Venus was conspicuous in the evening sky throughout the Festive Season, but although many members look at the planet from time to time, not many observe it seriously. At present the planet is rapidly approaching dichotomy (50% phase). Visual measurements of the phase are of interest in maintaining continuity in our records of the time of apparent dichotomy; sharp unprocessed images adequately exposed to show the true terminator will also be valuable. Apparent dichotomy arrives a few days early at an evening elongation, and will occur in about a week's time. Greatest elongation occurs on January 12, after which Venus will draw in towards the Sun, and inferior conjunction will be reached on March 25.
During the early part of 2017, Venus will be observable upon a dark sky, and therefore we shall have a really good opportunity to look for any sign of the famous 'Ashen Light' (AL) glow from the planet's dark side. Positive and negative observations are requested, and checking for this phenomenon will be worthwhile once the phase has dropped to around 40% or less. Use of an occulting bar to hide the bright crescent is recommended. Well-exposed integrated light or visual waveband filter images will also be useful, but should be made with an infrared blocking filter. This opportunity to observe upon a dark evening sky comes but rarely in the eight year 'cycle' of ten successive elongations of the planet. In 1993, for example, several positive visual records of the AL were made by different BAA observers from February 14 till March 25, but eight years later in 2001 there were no satisfactory sightings. Back in 1953 there were many positive records by experienced observers such as R.M.Baum, M.B.B.Heath, P.A.Moore and C.Tombaugh.
Another useful type of observation will be to try to image the thermal emission from the dark side. Subtle details of the surface topography can be revealed by image enhancement, and generally the higher ground will have a lower albedo, due to the decrease in temperature with altitude. Recent evidence (Sky & Telescope, 2017 February, page 11) strongly suggests that Venus may still be volcanically active, and what are believed to be fresh lava flows over the summit of one large volcano showed enhanced temperatures during the ESA Venus Express mission. Therefore any albedo variations in current images compared with previous ones are of great interest.
For a selection of earlier results it will be worthwhile looking at the comprehensive 1991-98 and 1999-2007 BAA Venus reports posted at the Section's website, which is linked from the BAA homepage.
Please send your results to me regularly: all observers are welcome to contribute, whether new or experienced.
Thank you very much in advance, and a very Happy New Year.
Dr Richard McKim (Director, Mercury & Venus Section)
richardmckim@btinternet.com
2017 January 1
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BAA-ebulletin mailing list visit:
http://lists.britastro.org/mailman/listinfo/baa-ebulletin
(c) 2016 British Astronomical Association http://www.britastro.org/
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The evening elongation of Venus, 2017
Venus was conspicuous in the evening sky throughout the Festive Season, but although many members look at the planet from time to time, not many observe it seriously. At present the planet is rapidly approaching dichotomy (50% phase). Visual measurements of the phase are of interest in maintaining continuity in our records of the time of apparent dichotomy; sharp unprocessed images adequately exposed to show the true terminator will also be valuable. Apparent dichotomy arrives a few days early at an evening elongation, and will occur in about a week's time. Greatest elongation occurs on January 12, after which Venus will draw in towards the Sun, and inferior conjunction will be reached on March 25.
During the early part of 2017, Venus will be observable upon a dark sky, and therefore we shall have a really good opportunity to look for any sign of the famous 'Ashen Light' (AL) glow from the planet's dark side. Positive and negative observations are requested, and checking for this phenomenon will be worthwhile once the phase has dropped to around 40% or less. Use of an occulting bar to hide the bright crescent is recommended. Well-exposed integrated light or visual waveband filter images will also be useful, but should be made with an infrared blocking filter. This opportunity to observe upon a dark evening sky comes but rarely in the eight year 'cycle' of ten successive elongations of the planet. In 1993, for example, several positive visual records of the AL were made by different BAA observers from February 14 till March 25, but eight years later in 2001 there were no satisfactory sightings. Back in 1953 there were many positive records by experienced observers such as R.M.Baum, M.B.B.Heath, P.A.Moore and C.Tombaugh.
Another useful type of observation will be to try to image the thermal emission from the dark side. Subtle details of the surface topography can be revealed by image enhancement, and generally the higher ground will have a lower albedo, due to the decrease in temperature with altitude. Recent evidence (Sky & Telescope, 2017 February, page 11) strongly suggests that Venus may still be volcanically active, and what are believed to be fresh lava flows over the summit of one large volcano showed enhanced temperatures during the ESA Venus Express mission. Therefore any albedo variations in current images compared with previous ones are of great interest.
For a selection of earlier results it will be worthwhile looking at the comprehensive 1991-98 and 1999-2007 BAA Venus reports posted at the Section's website, which is linked from the BAA homepage.
Please send your results to me regularly: all observers are welcome to contribute, whether new or experienced.
Thank you very much in advance, and a very Happy New Year.
Dr Richard McKim (Director, Mercury & Venus Section)
richardmckim@btinternet.com
2017 January 1
==============================
BAA-ebulletin mailing list visit:
http://lists.britastro.org/
(c) 2016 British Astronomical Association http://www.britastro.org/
==============================
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Good Clear Skies
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Astrocomet
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Colin James Watling
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Various Voluntary work-Litter Picking for Parish Council (Daytime) and also a friend of Kessingland Beach (Watchman)
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Real Astronomer and head of the Comet section for LYRA (Lowestoft and Great Yarmouth Regional Astronomers) also head of K.A.G (Kessingland Astronomy Group) and Navigator (Astrogator) of the Stars (Fieldwork)
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Lyra Main Website: http://www.lyra-astro.co.uk/
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