What is "sagitta"

Sagitta \Sa*git"ta\, n. [L., an arrow.]

1. (Astron.) A small constellation north of Aquila; the Arrow.

2. (Arch.) The keystone of an arch. [R.]
   --Gwilt.

3. (Geom.) The distance from a point in a curve to the chord; also, the versed sine of an arc; -- so called from its resemblance to an arrow resting on the bow and string.

4. (Anat.) The larger of the two otoliths, or ear bones, found in most fishes.

5. (Zo["o]l.) A genus of transparent, free-swimming marine worms having lateral and caudal fins, and capable of swimming rapidly. It is the type of the class Ch[ae]tognatha.

n. 1 The keystone of an arch. 2 (context geometry English) The distance from a point in a curve to the chord; also, the versed sine of an arc; so called from its resemblance to an arrow resting on the bow and string. 3 (context anatomy English) The larger of the two otoliths, or ear bones, found in most fishes.

Sagitta is a dim but distinctive constellation in the northern sky. Its name is Latin for " arrow", and it should not be confused with the larger constellation Sagittarius, the archer. Although Sagitta is an ancient constellation, it has no star brighter than 3rd magnitude and has the third-smallest area of all constellations (only Equuleus and Crux are smaller). It was included among the 48 constellations listed by the 2nd century astronomer Ptolemy, and it remains one of the 88 modern constellations defined by the International Astronomical Union. Located to the north of the equator, Sagitta can be seen from every location on Earth except within the Antarctic circle.

The red giant Gamma Sagittae is the constellation's brightest star, with an apparent magnitude of 3.47. Two star systems have been found to have planets.

In geometry, the sagitta (sometimes abbreviated as sag) of a circular arc is the distance from the center of the arc to the center of its base. It is used extensively in architecture when calculating the arc necessary to span a certain height and distance and also in optics where it is used to find the depth of a spherical mirror or lens. The name comes directly from Latin sagitta, meaning an arrow.

In optics and especially telescope making, sagitta is a measure of the glass removed to yield an optical curve. It is approximated by the formula

$S = \frac{r^2}{2 \times \text{ROC}}$

or

$S = \frac{r^2}{4 \times \text{focal length}}$

A good explanation both of this approximate formula and the exact formula can be found at http://www.opticampus.com/popcourse.php?url=high_powered/#appendix

Sagitta is a constellation.

The word may also refer to:

• Sagitta (optics), a measure of the glass removed to yield an optical curve
• Sagitta (geometry), the depth of an arc
• Versine, a trigonometric function
• Sagitta (genus), the chief genus of Chaetognatha including the largest arrowworms
• N.V. Vliegtuigbouw 013 Sagitta, glider

According to traditional Chinese uranography, the modern constellation Sagitta is located within the northern quadrant of the sky, which is symbolized as the Black Tortoise of the North (北方玄武, Běi Fāng Xuán Wǔ).

The name of the western constellation in modern Chinese is 天箭座 (tiān jiàn zuò), meaning "the heavenly arrow constellation".

Sagitta is a genus of arrowworms, small marine worms.

This genus is characterized in part by the distribution of the cilia on the body, the thick rays in the fins, and hooks which are not serrated.

As of 2007 there are 15 species. More have since been described.

Species include:

• Sagitta abyssicola
• Sagitta bedoti
• Sagitta bipunctata
• Sagitta bruuni
• Sagitta euneritica
• Sagitta euxina
• Sagitta glacialis
  • S. g. baltica
  • S. g. glacialis
• Sagitta izuensis
• Sagitta kussakini
• Sagitta modesta
• Sagitta nagae
• Sagitta nutana
• Sagitta pulchra
• Sagitta sceptrum
• Sagitta setosa
• Sagitta sublica