Asterisms in LaTeX

Another \LaTeX trick this week: asterisms. Asterisms are typographic devices used to separate or to call attention to a piece of text without resorting to using a section or chapter. While its usage in modern English (and French, for that matter) is now rare, it is still an interesting device to structure text.

The usual manifestation of an asterism is the ⁂ symbol (U+2042) but the single character asterism may not be suitable for all occasion. In HTML, and in these posts, you have seen it quite often. With \LaTeX, getting an decent-looking asterism is not that easy.

Using HTML, the asterism is most easily created:

<p align=center>*<br>*&emsp;*</p>

This creates a paragraph and renders as:

*
* *

which is the desired result. The most interesting thing in this construct is the &emsp;, the EM space is based on the em, the vertical space between two baselines of text. This gives an almost equilateral triangle (about 15% off), regardless of actual font size.

In \LaTeX, we can get fancier. First, we can use something else than the basic asterisk * as base motif (there are interesting dingbats that may do better depending on the type of text you’re writing). Second, we can get a lot fancier with spacing.

My current macro for asterism, given by:

%
%     *
%   *   *
\newcommand{\aster}{*} % maybe \ding{97} ?
\newcommand\asterism{
   \begin{center}
     \vspace{-1.75em}
     \parbox{1in}{ % needed to prevent split across page boundaries
       \begin{center}
         \aster\\
         \aster\hspace{1.15em}\aster
       \end{center}
     } %\parbox
     \vspace{-0.75em}
   \end{center}
 }

includes provisions for unwanted page breaks, forces centering, etc., and using \asterism yields:

The constant 1.15em comes from the fact that the base of an equilateral triangle of height 1 is \approx{}1.15. If the triangle has a height of one inter-baseline distance (1 em), the base is \approx{1.15} em. Indeed, the height of a triangle of side 1 is \frac{\sqrt{3}}{2}\approx{}0.8660, and if we normalize the height, the base of length 1 becomes of length \frac{2}{\sqrt{3}}\approx{}1.1547. Therefore, the above \LaTeX renders more or less as an equilateral triangle regardless of actual font size and line spacing.

3 Responses to Asterisms in LaTeX

  1. Fredrik Arnerup says:

    Also some code on the wikipedia page:
    http://en.wikipedia.org/wiki/Asterism_(typography)

  2. pferor says:

    An asterism is one character width and height. Your asterism is thee lines height, and three characters width.

    This is the real asterism:
    \newcommand{\asterism}{\smash{%
    \raisebox{-.5ex}{%
    \setlength{\tabcolsep}{-.5pt}%
    \begin{tabular}{@{}cc@{}}%
    \multicolumn2c*\\[-2ex]*&*%
    \end{tabular}}}}

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s

%d bloggers like this: