Octavio Paz

In the foreward to Piedra de sol Paz seems to state that the planet Venus is visible twice each day, morning and evening.

That is not the sense in which the Morning Star is, in fact, the Evening Star.

Perhaps those maintaining the ancient Mexican calendar would have appreciated Galileo's "spyglass" views of the cycles of Venus and her varying apparent diameter and their association with morning and evening.

From 45deg N. latitude in this 10th month of 2010, Venus and Saturn are both more than 10 degrees from the daytimne sun.  But how to see them?  Saturn sets moments before the sun and venus moments later due to their being now at about the same altitiude as the sun relative to the horizon.

It has been suggested that Venus cannot be seen in daylight when within 10 degrees of the sun - but their would be occasions when Venus as the "Evening Star" could be detected as a "Daytime star" and that Venus as the "Morning Star" could be successfully tracked during the day (as can be done with Jupiter this season?)

Mercury, however, is now so close to the sun as to be "gone" from the sky.  Mars is to faint to be seen except duing a solar eclipse (?).

It would seem more likely that the Aztec's knew their Venus as a star of two cycles.  And then there is the importance of the Pleiades and Doomsday (see Fray Bernardino de Sahagun.)

The Maya, in particular, (per Dreseden Codex?) allotted distinct time periods to the Venus no longer visible.

see: heliacal rising of Venus

Viewing daylight Venus link: http://www.fourmilab.ch/images/venus_daytime/