Ancient mounds in Japan reveal celestial preoccupation

Sacred monuments

Japan is dotted with dozens of keyhole-shaped burial mounds called “kofuns” that were constructed between AD 300 and AD 700. One of the most famous is the Hashihaka kofun, located in the heart of the country very near the sacred mountain Miwayama. The Hashihaka kofun, built up with stones and earth, rises from the surrounding plain. It is 886 feetlong and its round “keyhole” section is 89 feet high. Since its construction around AD 300, it has become overgrown with trees, forming a dense copse on the treeless plain. All of the kofuns are burial tombs and legend has it that a powerful female ruler rests at Hashihaka. Of more interest to astronomers is the fact that the kofun is aligned so that the keyhole not only aligns with Miwayama but marks the precise point on the horizon where the midwinter sunrise occurs. The reverse direction marks the point of the midsummer sunrise. This type of construction, marking equinoxes, solstices or cross-quarter days, is common among agricultural peoples. The Japanese, whose principal crop was rice, had just such a preoccupation with the celestial calendar.

Focus on the planets

All five naked-eye planets are on the same side of the sun and visible during the evening hours of the first week of April. This viewing bonanza will not be duplicated until the year 2036.

Mercury appears low on the western horizon at dusk as April opens. Don’t delay if you want to catch a glimpse of the innermost planet, for it disappears from view by the end of the first week of the month.

Venus dominates the western sky during the early evening hours, easily outshining any other planet or star. The beauty of Venus is enhanced by its close proximity to the Pleiades during the first days of the month.

Mars lies to the upper left of Venus as April opens but is far fainter than its brilliant neighbor. Look for Mars as a dull orange dot near much brighter Aldebaran, the eye of the Bull.

Jupiter may be found high in the south at sunset among the stars of Leo the Lion. Although fainter than Venus, it appears larger and a telescopic examination reveals details such as the Great Red Spot, the equatorial belts and the four major moons as they trek across the face of the planet.

Saturn is high in the southwest, to the upper left of Mars and Venus, and is at dusk close to the twin stars of Gemini.

Uranus is in Aquarius and Neptune in Capricornus. Both may be spotted with a good pair of binoculars. A chart showing where to look may be found in this month’s issue of Sky & Telescope.

Pluto is in Ophiuchus, where it is lost to view except for near-professional quality telescopes.

April events

1 Sunrise, 5:17 a.m.; sunset, 6:02 p.m. Look for Venus in very close proximity to the Pleiades tonight. Mars and Aldebaran are to the upper left while Mercury glows in solitary splendor to the extreme lower right.

4 First Sunday in April. Remember to set your clocks ahead an hour before you go to bed.

5 Full moon, 7:04 a.m. The full moon of April is known as the Grass Moon, Egg Moon or Full Pink Moon.

8 Moon at perigee, or closest approach to the Earth.

11 Easter. The old way of calculating the date of Easter was that it falls on the first Sunday after the full moon closest, but after, the spring equinox. This year the equinox was on March 20, the next full moon on April 5 and Easter on Sunday, April 11.

12 Moon in last quarter, 11:47 p.m.

18 The Sun enters Aries on the ecliptic.

19 New moon, 9:23 a.m. The sun enters the astrological sign of Taurus but, astronomically, has just entered Aries.

22 This is the peak night for the Lyrid meteor shower. Look for an average of 20 meteors per hour from high in the northeast out of the constellation of Lyra. The recent new moon will ensure a sky dark enough for good viewing.

23 The moon is at apogee or greatest distance from the Earth. Check out Venus to the moon’s lower right, faint Mars to its lower left and Saturn farther to the moon’s upper left.

27 Moon in first quarter, 1:33 p.m.

29 Jupiter shines just below the moon tonight. The pair is flanked by Regulus and Denebola of Leo the Lion.

30 May Eve. A cross-quarter day marking the midpoint between the spring equinox and the summer solstice. Sunrise, 5:27 a.m.; sunset, 7:39 p.m.

Clair Wood taught physics and chemistry for more than a decade at Eastern Maine Technical College in Bangor. He can be reached at cgmewood@aol.com.