http://www.phys.uu.nl/~vgent/venus/venus_text2.htm#black%20drop
Bibliography: The Black Drop and Related Phenomena, from R.H. van Gent

http://www.transitofvenus.org/faq/298-what-causes-the-black-drop-effect
FAQ: What causes the Black Drop Effect? A simplified explanation of limb darkening and point-spread function, courtesy of Jay Pasachoff.

http://nicmosis.as.arizona.edu:8000/POSTERS/TOM1999.jpg
Poster on the 1999 transit of Mercury "definitively solves the problem of the black-drop effect that plagued past transits of Venus;" by Jay Pasachoff, Glenn Schneider and Leon Golub; from the American Astronomical Society's Division of Planetary Science meeting in 2001.

http://arxiv.org/pdf/astro-ph/0310379
Report by Schneider, Pasachoff, and Golub (see poster above) "separates the primary contributors to [the "Black Drop" Effect], solar limb darkening and broadening due to the instrumental point spread function...for the 1999 transit of Mercury, seen in high spatial resolution optical imaging with NASA's TRACE spacecraft."

http://www.aas.org/publications/baas/v32n4/aas197/785.htm
Abstract describes physical cause of "black drop" effect; B. E. Schaefer (Univ. Texas Austin) at 2001 AAS meeting.

From footnote 28 of  Chapter 7 of Sky and Ocean Joined: U.S. Naval Observatory, 1830-2000, by Steven J. Dick, (Cambridge University Press, 2003):

"The physical cause of the black drop phenomenon has been the subject of considerable controversy. Bradley Schaefer reviews the controversy in “The Transit of Venus and the Notorious Black Drop,” BAAS, 32 (2000), 1383-1384. He concludes that the phenomenon is not caused by diffraction, illusion or atmospheric refraction, but by terrestrial atmospheric smearing that blurs the image."

http://www.bo.astro.it/~biblio/Horn/Blackdrop.htm
Origin and Phases of the "Black Drop" Phenomenon, a paper on the understanding of the black drop effect as of 1922.  Also available in Italian; from Guido Horn D'Arturo of Università di Bologna, Dipartmento di Astronomia, 1922. 

http://skyandtelescope.com/news/article_1277_1.asp
Sky & Telescope magazine asks, "Where Was the Black Drop?" after the 2004 transit of Venus.

To simulate the appearance of the "black drop" effect, almost pinch your thumb and forefinger together against a bright background.  Near contact the ligament between them appears.

http://vestige.lmsal.com/TRACE/transits/venus_2004/
Images and movies from the TRACE spacecraft are among many new perspectives of the 2004 transit of Venus.

At the critical moment when observers try to time when Venus touches the inside edge of the sun, strange phenomena such as the black drop effect suddenly emerge.  This site guides observers in discerning at what instant internal contact occurs; from Steven van Roode.

http://star.arm.ac.uk/history/transit.html
Drawings of the Transit of Venus by Captain James Cook and Charles Green; from the Armagh Observatory.

http://www.metaresearch.org/home/Viewpoint/blackdrop.asp
In noting "an irradiation effect – the apparent spreading of light from bright areas onto any adjacent dark areas," author Tom Van Flandern asserts that the well-understood black drop effect "provides a timing advantage rather than a disadvantage." 

http://www.bo.astro.it/~biblio/sma/page/venere_05_06_1761.html
Bibliographical and archival records from the Department of Astronomy of the University of Bologna (Italy), featuring manuscripts of observations made in Bologna by Eustachio Zanotti; includes images and resources from transits in addition to the 1761 records.  (Italian; a link with some English translation is at http://www.bo.astro.it/~biblio/Archives/copertina.html.)

http://www.bo.astro.it/~biblio/Horn/Blackdrop.htm
A detailed 1922 assessment of the black drop effect suggests "instrumental astigmatism should be considered the cause of some aspects of the photographedGUIDO HORN D’ARTURO The “black drop” phenomenon and astigmatism. Università di Bologna, Dipartimento di Astronomia, (Pubblicazioni dell’Osservatorio astronomico della R. Università di Bologna, vol. I, n.3, 1922). ligaments." 

Read more: Links: Black Drop Effect

http://eclipse.gsfc.nasa.gov/SENL/SENL200407B.pdf
Reports of 2004 Transit of Venus; from Solar Eclipse Newsletter (SEN).  See Volume 9, Issue 7, pages 47-80.  SEN captures excerpts from dialogue on blogs and listserves that discuss accounts of seeing the 2004 transit of Venus and its implications.

history/2004/195-2004-transit-of-venus-images
Diverse images and video of the 2004 transit of Venus from sites around the world (and in space, too); from professional and amateur observers alike.  Shown are Dutch Open Telescope image and an image projected through a telescope.


http://sxidata.ngdc.noaa.gov/archive/browse/special/SXI_SPECIAL_20040608_VENUS_09H.MPG
In images by the GOES satellites Solar X-Ray Imager (SXI), Venus appears as a dark disk about 1/30th the Sun’s apparent diameter. Since the Sun’s corona extends well above the disk, Venus was visible in silhouette for approximately 9 hours, versus the 6 hours seen from Earth. The path across the disk is from the southeast to the southwest.  Movie (1.9 MB MPEG-1, 7 sec.) was created by NOAA's Space Weather Prediction Center.



2004 Transit of Venus Map shows world visibility in 3 colors for simplicity. 

http://www.youtube.com/watch?v=qS1O6C2dQ40
Video: A crowd gathered before sunrise on June 8, 2004, to witness the rare Transit of Venus in Mishawaka, Indiana, USA. Though clouds threatened to obscure the spectacle, the sun emerged in time for the audience to observe through telescopes, rear projection screens, and solar viewers. An audible time signal in the background allowed individuals to time the instant when the black dot of Venus just touched the inside edge of the sun, as global expeditions had done in past centuries. The last transit of Venus in our lifetimes occurs June 5-6, 2012.

images/stories/congrats.jpg
U.S. Secretary of Education Rod Paige congratulates the Penn-Harris-Madison Corporation and its families for global outreach related to the 2004 Transit of Venus.

http://home.comcast.net/~edwelda/site/?/page/Transit_of_Venus/
A First-in-a-Lifetime Transit; an account of the 2004 Transit of Venus, by Imelda B. Joson.

http://kepler.nasa.gov
"NASA Kepler Mission is searching the skies for planets that are the same size as Earth--worlds that could possibly be similar to our own."  The spacecraft identifies transiting planets as it scans more than 100,000 stars near the constellation Cygnus, looking for recurring dips in the light curve.  Excellent website with many resources, including:

• Classroom Activities
  
• Formal Education, Informal Education, and Public Outreach
  
• Models and Simulations
  
• and much more.

http://planetquest.jpl.nasa.gov/
PlanetQuest Exoplanet Exploration is an engaging site for news and multimedia about NASA's search for new worlds.  Keep pace with current tally of new and candidate planets; get your questions answered by Astronomer Steve; create your planet with Extreme Makeover; check out the great videos from multiple NASA missions, and always see the latest exoplanet news at the forefront of science. 

http://kepler.nasa.gov/files/mws/TransitTracks-7-2010.pdf
Transit Tracks is an investigation in which students describe a transit and the conditions when a transit may be seen; describe how a planet’s size and distance from its star affects the behavior of transits; and interpret graphs of brightness vs time to deduce information about planet-star systems.

   http://oklo.org/
The Systemic Weblog, written by Greg Laughlin, reports recent developments in the field of extrasolar planets, with a particular focus on observational and theoretical astronomical research work.  Tutorials show how to use the Systemic Console, a program that "uses an intuitive graphical interface to analyze data in order to detect and characterize planets."

http://www.transitsearch.org/
An observing program whose purpose is "to coordinate and direct a cooperative observational effort which will allow experienced amateur astronomers and small college observatories to discover transiting extrasolar planets."  To observe transiting planets around distant stars, you need a telescope with an accurate clock drive, a CCD camera, and appropriate computer software.  Observers who obtain photometry of known transiting planets can submit their light curves.  The transitsearch.org site currently functions primarily as an ephemeris information service.

http://www.planethunters.org/
Actually find new planets orbiting distant stars using the data from the Kepler mission.  Participants steer astronomers to candidate stars by judging the existence of patterns in a light curve.  From Planet Hunters.

http://www.wnit.org/outdoorelements/1000/1003/1003.html
Planetarium director Ruth Craft uses a photometer and orrery to simulate the Kepler spacecraft monitoring a star with transiting planets.  In the demonstration, computer software generates a light curve that is projected on the domed ceiling, where visitors can discern the presence and characteristics of companion planets.  See How the Kepler Telescope Works (Segment #3 of Episode #1003); from WNIT Outdoor Elements.

http://smsc.cnes.fr/COROT/
COROT (COnvection, ROtation and planetary Transits) space telescope is international venture launched in December, 2006; it uses stellar seismology to examine the inner structure of stars and a CCD camera to detect the transits of extrasolar planets.  See sidebar in March 2009 Planetarian, page 10.

http://www.mykepler.com/
MyKepler is an educational program with a vision to involve 3,000 schools (1,000 in the USA) in the tracking and exploration of the Kepler telescope data to discover earth-like planets in the close Milky Way proximity.

http://www.planetary.org/explore/topics/extrasolar_planets/extrasolar/transit_photometry.html
Extrasolar Planets: Transit Photometry Method for Finding Earths; from Planetary Society.

http://www.ati.ulg.ac.be/TRAPPIST/Trappist_main/Home.html
TRAPPIST: TRAnsiting Planets and Planetesimals Small Telescope

A crowd gathered before sunrise on June 8, 2004, to witness the rare Transit of Venus in Mishawaka, Indiana, USA. Though clouds threatened to obscure the spectacle, the sun emerged in time for the audience to observe through telescopes, rear projection screens, and solar viewers. An audible time signal in the background allowed individuals to time the instant when the black dot of Venus just touched the inside edge of the sun, as global expeditions had done in past centuries. The last transit of Venus in our lifetimes occurs June 5-6, 2012.  YouTube video at http://www.youtube.com/watch?v=qS1O6C2dQ40.