CONSTELLATIONS BY SEASON
the northern evening sky through the year: 28 constellations per the Yale Bright Star Catalogue, latitude 40° N, evenings near 9 pm
US$1.50
METEOR SHOWERS
the twelve principal showers of the year · periods, peaks and ZHR per the IMO calendar
US$1.50
PHASES OF THE MOON
eight phases · a full cycle of 29.53 days
US$1.50
SPRING AND NEAP TIDES
the Earth–moon–sun geometry that makes the tides swing — after NOAA
US$1.50