black drop


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black drop

An optical phenomenon seen near the beginning and end of transits of Venus and Mercury across the Sun's disk. It takes the form of an apparent elongation of the planet's silhouette against the solar surface, with a link being formed between the silhouette and the dark sky beyond the Sun's limb, as seen in photographs and telescopic projections. The effect makes the planet look rather like a teardrop. It appears to be caused by a combination of instability in the Earth's atmosphere (see seeing) and the resolving power and sensitivity of the observing instrument being used. The black drop effect was a major factor in reducing the accuracy of early attempts to determine the solar parallax by observing transits from different parts of the Earth in the 18th and 19th centuries. During the transit of Venus in 2004, a large number of astronomers failed to notice the black drop effect at all, probably because of technical improvements that have been made in modern telescopes.

black drop

[¦blak ′dräp]
(astronomy)
As seen through a telescope, an apparent dark elongation of the image of Venus or Mercury when the planets' images are at the sun's limb.
References in periodicals archive ?
With two owners, Oppelaar said the Black Drop will now be able to work with more nonprofit organizations.
He sought relief in something called the Kendal Black Drop, a quack cure-all which basically inflamed the problem since it contained even more opium mixed with vegetable acids, which left him with violent stomach pains.
The setting by Jean Paul Vroom, a rippling curtain of pale blue seen through a rectangle cut from a black drop, reflected this bailers formality and freedom.
Standard amenities include 12 volt trigger, IR / remote, and 24 inches of extra black drop making the Performance Motorized the ultimate solution for any home theater application.
Nelson replaces Louis Ludik at full-back while Chris Henry and Callum Black drop out and Iain Henderson moves to lock in place of Franco van der Merwe.
the existence of a ring of light round the planet and of one or more bright spots near the centre of the disk, and the phenomena of the black drop, which deserves special attention.
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Blue chandelier earrings, pounds 12, Topshop; Rachel Bilson; Purple diamante earrings, pounds 8, Wallis; Eva Longoria; Black drop earrings, pounds 7.
We looked superb last week, yet Mr Black drops Stephen Warnock in favour of another striker.
If you look at just fishing the number rises slightly, to 6 percent; but when you look at hunting alone, the number of hunters who are black drops to 2 percent.
35pm Actor Jack Black drops in to talk about his new film Year One, Sue Perkins and Giles Coren discuss their documentary series The Supersizers Eat and Take That return to the studio.