4.3. UNITS

23

A free-format floating-point value follows the same rules as a fixed-format floating-

point value except that the ASCII representation may occur anywhere within bytes 11

through 80.

4.2.5

Complex Integer Number

There is no fixed-format for complex integer numbers.1

If the value is a complex integer number, the value must be represented as a real

part and an imaginary part, separated by a comma and enclosed in parentheses e.g.,

(123, 45). Spaces may precede and follow the real and imaginary parts. The real and

imaginary parts are represented in the same way as integers (§4.2.3). Such a represen-

tation is regarded as a single value for the complex integer number. This representation

may be located anywhere within bytes 11 through 80.

4.2.6

Complex Floating-Point Number

There is no fixed-format for complex floating-point numbers.1

If the value is a complex floating-point number, the value must be represented as a

real part and an imaginary part, separated by a comma and enclosed in parentheses,

e.g., (123.23, -45.7). Spaces may precede and follow the real and imaginary parts.

The real and imaginary parts are represented in the same way as floating-point values

(§4.2.4). Such a representation is regarded as a single value for the complex floating-

point number. This representation may be located anywhere within bytes 11 through

80.

4.3

Units

When a numerical keyword value represents a physical quantity, it is recommended that

units be provided. Units shall be represented with a string of characters composed of

the restricted ASCII text character set. Unit strings can be used as values of keywords

(e.g., for the reserved keywords BUNIT, and TUNITn), as an entry in a character string

column of an ASCII or binary table extension, or as part of a keyword comment string

(see §4.3.2, below).

The units of all FITS header keyword values, with the exception of measurements

of angles, should conform with the recommendations in the IAU Style Manual [19].

For angular measurements given as floating-point values and specified with reserved

keywords, the units should be degrees (i.e., deg). If a requirement exists within this

standard for the units of a keyword, then those units must be used.

The units for fundamental physical quantities recommended by the IAU are given

in Table 4.1, and additional units that are commonly used in astronomy are given in

1

This requirement differs from the wording in the original FITS papers. See Appendix H.

FITS Standard