Buddhist monk used shaft, sun to measure year length

Sacred monuments

One of the earliest astronomical measurements made was the length of the year. A shaft called a gnomon was set in the ground perpendicular to the horizon and the length of the shadow cast measured at the same time each day. The sun’s midday altitude would be at its highest and the shadow cast shortest at the summer solstice. The sun’s altitude would be lowest and the midday shadow cast the longest at the winter solstice. By measuring the time between two summer or winter solstices, each having shadows of exactly the same length, the ancients were able to determine the length of the year within a few minutes. One place where this was done was at Gao Cheng Zhen, a sacred city the Chinese considered to be the center, or “navel,” of the world. In the year A.D. 725 a Buddhist monk placed a gnomon at the temple in Gao Cheng Zhen and measured the length of the year to “great exactitude,” according to one source.

Focus on the planets

Mercury may be spotted low on the southwest horizon about an hour after sunset as July opens. Look for Mercury on July 1 with Castor and Pollux to its upper right and dim Mars approximately the same distance to its upper left.

Venus rises in the east at dawn during early July but is up three hours before the sun by month’s end. With its historic transit in the past, Venus will continue to intrigue viewers with a thin crescent appearance.

Mars is low and faint in the west an hour after sunset at the beginning of July. On July 1, much brighter Mercury is to the lower right. Look for an extremely close pairing of the two planets on July 10 at dusk.

Jupiter is well up on the western horizon at dusk affording an easy target for viewing of both the giant planet and some of its moons.

Saturn spends most of July hidden behind the sun emerging late in the month to peek above the predawn horizon to the lower left of Venus.

Neptune rises in the southeast among the stars of Capricorn around 10 p.m. It is followed about an hour later by Uranus in Aquarius. Both may be accessible with powerful binoculars and the aid of a finder’s chart such as appears in the April issue of Sky & Telescope.

July events

1 Sunrise, 4:53 a.m.; sunset, 8:25 p.m. Moon is at perigee, or closest approach to the Earth, tonight. With its proximity to the full moon, look for abnormally high tides. Venus is the brilliant “morning star” low in the northeast at dawn.

2 Full moon, 7:09 a.m. The full moon of July is known as the thunder moon, hay moon, or buck moon. The midpoint of the year is given as occurring at 1 a.m. today.

5 The Earth is at aphelion, or furthest distance from the sun, today. If you are up late, look for Mars in the Beehive cluster around 4 a.m.

9 Moon in last quarter, 3:34 a.m.

10 Look for an extremely close conjunction or pairing of Mercury and Mars low in the northwest at dusk.

14 Moon at apogee, or greatest distance from the Earth, today. Note that the moon is directly to the left of Venus an hour before dawn. Aldebaran is to the upper right of Venus.

17 New moon, 7:24 a.m.

18 Look to the west-northwest about an hour after sunset where a thin crescent moon lies to the immediate upper right of Mars. Then, starting with Mars and moving in an upper-left direction, locate Mercury, Regulus and Jupiter in that order.

20 The sun enters Cancer on the ecliptic. Jupiter is to the left of the crescent moon at dusk.

21 The crescent moon is to the upper left of Jupiter in the west at twilight. Regulus, Mercury and Mars trail far to the lower right.

22 The Sun enters the astrological sign of Leo even though, astronomically, it has just entered Cancer.

25 Moon in first quarter, 11:38 p.m. Check out the western horizon an hour after sunset where Mercury and Regulus are close together. Mars is to the lower right, and Jupiter to the upper left of the pair respectively.

30 The moon is at perigee, or closest approach to the Earth, today.

31 Full moon, 2:05 p.m. This is the second full moon of July. While some refer to it as the full sturgeon moon, we know it as the blue moon. Sunrise, 5:19 a.m.; sunset, 8:03 p.m.

Clair Wood taught physics and chemistry for more than a decade at Eastern Maine Technical College in Bangor.