An Etymological Dictionary of Astronomy and Astrophysics
English-French-Persian

The appearance of a band linking the solar limb to the disk of a transiting planet (Venus or Mercury) near the point of internal tangency. This effect increases the uncertainty in measuring the period from when the planet fully enters the solar disk to when it begins to depart. Historically, the black drop phenomenon limited the accuracy of the determination of the Astronomical Unit and the scale of the Solar System in the 18th and 19th centuries. While there have been many proposed theories over the years, the true cause of the effect was revealed during a transit of Mercury in 1999, which was observed by the NASA's TRACE satellite. Two effects could fully explain the black drop: the inherent blurriness of the image caused by the finite size of the telescope (→ point spread function), and an extreme dimming of the Sun's surface just inside the apparent outer edge (→ limb darkening). See Schneider et al. 2004, Icarus 168, 249.

→ black; → drop.

1a) A small quantity of liquid that falls or forms in a round or pear-shaped mass.
1b) A very small quantity of liquid; a very small quantity of anything.
2) To fall in small portions, as water or other liquid.

M.E. drop(e), from O.E. dropian; related to O.H.G. triofan, Du. drop, Ger. Tropfen.

Cekké, cekidan "drop; small, minute," cekidan "to drop."

A very small drop of a liquid.

→ drop + diminutive suffix let.

To listen secretly to a private conversation.

Probably back-formation from → eavesdropper.

Gušârdan, from gušâr, → eavesdropper, + -dan infinitive suffix.

A person or thing that secretly listens to or monitors the private conversation or data of others.

From M.E. eavesdrop, from O.E. yfesdrype "place around a house where the rainwater drips off the roof," literally "one who stands on the eavesdrop in order to listen to conversations inside the house," from eaves "the lower border of a roof that overhangs the wall" + drip, drop "to fall in small portions."

Gušâr in Tabari "eavesdropper," from guš, → ear, + -âr probably contraction of dâr (as in dustâr/dustdâr) agent noun from dâštan "to hold, have, possess; appoint, erect," → property.

The monitoring and/or examining the data that is passed over the network without sender and receiver's permission and/or knowledge. For example, a user on the Internet could eavesdrop on someone's phone conversation or e-mail.

Noun from → eavesdrop.

A precision experiment for measuring the → electron charge. By studying the falling speed of small charged droplets in the gravitational field of the Earth subjected to an adjustable electric field, Millikan (1909) was able to demonstrate conclusively the discrete nature of electric charge, and moreover measure the charge of an individual electron.

Robert Andrews Millikan (1868-1953); → experiment.