# Symbols:A

### atto-

$\mathrm a$

The Système Internationale d'Unités symbol for the metric scaling prefix atto, denoting $10^{\, -18 }$, is $\mathrm { a }$.

Its $\LaTeX$ code is \mathrm {a} .

### are

$\mathrm a$

The are is a measure of area:

One are is equal to a square whose side measures $10$ metres.

 $\ds$  $\ds 1$ are $\ds$ $=$ $\ds 100$ square metres $\ds$ $\approx$ $\ds 119 \cdot 60$ square yards

$\mathrm A$ or $\mathrm a$

The hexadecimal digit $10$.

Its $\LaTeX$ code is \mathrm A  or \mathrm a.

### Celestial Altitude

$a$

Let $X$ be a point on the celestial sphere.

The (celestial) altitude of $X$ is defined as the angle subtended by the the arc of the vertical circle through $X$ between the celestial horizon and $X$ itself.

It is often denoted by $a$.

### Azimuth (Astronomy)

$A$

Let $X$ be a point on the celestial sphere.

The spherical angle between the principal vertical circle and the vertical circle on which $X$ lies is the azimuth of $X$.

The azimuth is usually measured in degrees, $0 \degrees$ to $180 \degrees$ either west or east, depending on whether $X$ lies on the eastern or western hemisphere of the celestial sphere.

It is often denoted by $A$.

### Ampere

$\mathrm A$

The symbol for the ampere is $\mathrm A$.

Its $\LaTeX$ code is \mathrm A .

### Angstrom

$\mathring {\mathrm A}$

The symbol for the angstrom is $\mathring {\mathrm A}$.

Its $\LaTeX$ code is \mathring {\mathrm A} .

### Alternating Group

$A_n$

### Inverse

a-

Prefix indicating anti.

An abbreviation for arc, anti- or argument.

### Not

a-

Prefix indicating not.