A diagonal star table is a grid filled with the names of stars written in the hieroglyphic script. In order to describe the parts and contents of diagonal star tables and introduce the terms it is convenient to refer to a model or "ideal" diagonal star table. It is important to remember that not one of the surviving tables follows the ideal exactly, but all have elements in common with it.
This is a description of the features of the ideal diagonal star table shown above:
The table reads from right to left. It is divided into quadrants by a vertical strip (VS) and a horizontal strip (HS). The table is headed by a date row (DR) containing thirty-six decade labels, one for each 10-day period ("decade") in the Egyptian civil year. There are twelve further rows (six above the horizontal strip, six below). Each decade label therefore heads a column of twelve cells, each containing the name of a decan. A decan is a star or small group of stars which first appears in this type of table. Decans also appear in later Egyptian astronomical texts outside the context of diagonal star tables.
After the 36 columns headed by decade labels, a further four list columns (C1 to C4) complete the table. The fourth and final list column contains a label indicating that it relates to the five epagomenal days at the end of the 365-day Egyptian civil year.
Each star name in the ideal table is represented by a number (1-36) or a letter (A-L). The star names move diagonally across the table. This feature gives the tables their modern name: diagonal star tables. The 36 numbered decans are called ordinary decans; the lettered decans are called triangle decans because of the shape they make in the table.
The list columns contain a complete, ordered list of all the decans used in the table. The decan list is a characteristic of an individual diagonal star table. It can also be reconstructed by reading down the first column and along the final row. The twelfth triangle decan, L, occurs only once in the entire table, at the end of the fourth list column. Decan 1 appears twice, once in the top-right cell of the diagonal star table and once in first place in the list columns. Decans 2-11 appear 3 to 12 times respectively (as do the other triangle decans counting backwards L through to A). Decans 12-36 each appear exactly 13 times.