One can use astrology to predict (or try to predict 😉 ) daily highs/lows by looking at the aspects formed by transiting planets to each other and/or the main horoscope axis points (AC, DC, MC, and IC). I’d say MC and AC are probably the strongest “triggers.”
There are other cycles in play too of course (e.g., unfolding of energies from slow moving planetary alignments) and I recommend monitoring transits/progressions to any relevant charts of whatever one is investing in (e.g., stocks), but simply monitoring daily aspects gives a general hint of the direction.
Specifically, “negative” planets, like Pluto and Saturn, conjunct or square any axis point (or each other, or other planets, esp. Mars or Uranus) tend to manifest as fear or suppression (market is approaching a low point or there is a reversal going down shortly before the aspect becomes exact), whereas aspects formed by the “positive” Jupiter typically manifest as reversals up and/or market approaching a high point shortly before the aspect is exact.
For example, a major MIN for DJI on Oct 20, 2011 occured at 12:20pm EST. The astro chart for NYC shows that at 12:20pm EST, the Saturn was exactly conjunct MC at 21 degrees of Libra.
DJI chart and astro chart for Oct 20, 2011 at 12:20pm (EST NYC)
DJI chart came from http://www.google.com/finance?q=INDEXDJX:.DJI#
Astro chart (free) came from www.astro.com