Online Encyclopedia

Search over 40,000 articles from the original, classic Encyclopedia Britannica, 11th Edition.

TWILIGHT

Online Encyclopedia

Originally appearing in Volume V27, Page 492 of the 1911 Encyclopedia Britannica.

» Make a correction to this article.
» Add information or comments to this article.

Encyclopedia Home :: TUM-VAN

Spread the word:

del.icio.us it!

TWILIGHT , formerly known as Crepusculum (a Latin word meaning dusky or obscure), properly the See also:

INTERVAL

interval during which the See also:

ATMOSPHERE (Gr. fir µ6r, vapour; orkaipa, a sphere)

atmosphere is illuminated after the setting of the See also:

sun. The analogous phenomenon in the See also:

MORNING

morning, i.e. the interval between the first See also:

APPEARANCE (from Lat. apparere, to appear)

appearance of See also:

LIGHT

light and the rising of the sun, is known as the See also:

DAWN (the 16th-century form of the earlier " Jawing " or " dawning," from an old verb " daw," O. Eng. dagian, to become day; cf. Dutch dagen, and Ger. tagen)

dawn. These phenomena are due to the light of the sun after See also:

refraction by the atmosphere being reflected to the observer by the clouds, dust, and other See also:

ADVENTITIOUS (from Lat. adventicius, coming from abroad)

adventitious See also:

MATTER

matter See also:

PRESENT

present in the atmosphere. Even in the See also:

early See also:

INFANCY

infancy of See also:

ASTRONOMY (from Gr. &arpov, a star, and v ,usiv, to classify or arrange)

astronomy, the duration of twilight was associated with the position of the sun below the See also:

HORIZON (Gr. 6pfTwv, dividing)

horizon, and measurements were made to determine the maximum See also:

VERTICAL (from Lat. vertex, highest point)

vertical depression of the sun which admitted the phenomena. This was found by See also:

ALHAZEN (ABU ALI AL-HASAN IBN ALHASAN)

Alhazen, Tycho See also:

Brahe and others, to be about 18°, and although other observers obtained somewhat different values, yet this value is now generally admitted. The duration of twilight is therefore measured by the See also:

time in which the sun traverses an arc of r8° of vertical depression, and primarily depends on the See also:

LATITUDE (Lat. latitudo, latus, broad)

latitude of the observer and the See also:

DECLINATION (from Lat. declinare, to decline)

declination of the sun. It is subject to several See also:

minor See also:

variations, occasioned by the variable amount of dust, clouds, &c. suspended in the See also:

air; and also on the temperature, which alters the See also:

ALTITUDE (Lat. altitudo, from altus, high)

altitude of the reflecting particles; thus at the same See also:

PLACE (through Fr. from Lat. platea, street; Gr. IrAar6s, wide)

place and on the same See also:

day, the morning twilight or dawn is generally shorter than the evening twilight. The duration and possibility of twilight may be geometrically exhibited as follows : Let 0 be the position of the observer (fig.

End of Article: TWILIGHT

Additional information and Comments

There are no comments yet for this article.

» Add information or comments to this article.

Please link directly to this article:
Highlight the code below, right click, and select "copy." Then paste it into your website, email, or other HTML.

Site content, images, and layout Copyright © 2006 - Net Industries, worldwide.
Do not copy, download, transfer, or otherwise replicate the site content in whole or in part.

Links to articles and home page are always encouraged.

[back]
TWICKENHAM

[next]
TWILL (connected with " two ")