  As of 2012 Jan 21, the Pan-STARRS 1 3\pi Survey has observed the 3/4 of the
sky visible from Hawaii with a minimum of 2 and mean of 7.6 observations in 5
filters, g_p1, r_p1, i_p1, z_p1, y_p1. Now at the end of the second year of the
mission, we are in a position to make an initial public release of a portion of
this unprecedented dataset. This article describes the PS1 Photometric Ladder,
Release 12.01 This is the first of a series of data releases to be generated as
the survey coverage increases and the data analysis improves. The Photometric
Ladder has rungs every hour in RA and at 4 intervals in declination. We will
release updates with increased area coverage (more rungs) from the latest
dataset until the PS1 survey and the final re-reduction are completed. The
currently released catalog presents photometry of \approx 1000 objects per
square degree in the rungs of the ladder. Saturation occurs at g_p1, r_p1, i_p1
\approx 13.5; z_p1 \approx 13.0; and y_p1 \approx 12.0. Photometry is provided
for stars down to g_p1, r_p1, i_p1 \approx 19.1 in the AB system. This data
release depends on the rigid `Ubercal' photometric calibration using only the
photometric nights, with systematic uncertainties of (8.0, 7.0, 9.0, 10.7,
12.4) millimags in (g_p1, r_p1, i_p1, z_p1, y_p1). Areas covered only with
lower quality nights are also included, and have been tied to the Ubercal
solution via relative photometry; photometric accuracy of the non-photometric
regions is lower and should be used with caution.
