Are there planets orbiting other star systems similar to Earth and capable of sustaining life? A recent report of the discovery of a planet about a far distant star has renewed interest in this possibility.

Planets do not emit light hence any search for them has to be an indirect one. In 1983, the Infrared Astronomical Satellite (IRAS) was put into orbit and found a cold disk of matter orbiting the star Vega in the constellation of Lyra. It is believed that our own planetary system formed from a rotating disk of matter orbiting the sun so the disk about Vega could be planets in the processing of forming.

If a star has a large, unseen companion orbiting it, the latter can be detected from changes in the star’s visible spectra. Using this type of evidence, astronomers have detected a possible planet, about the size of Jupiter, around Barnard’s star. Stars up to 1.5 times as large as the sun spin slower than larger stars.

One theory has it that these stars slowed down as newly formed planets applied gravitational “brakes” to their spin. The latest piece of evidence for planets comes from the irregular signal received from a distant pulsar. A pulsar gives off radio signals in a regular pattern unless some other object in the vicinity disturbs its orbit. The signal from the new pulsar changes by only one-hundreth of a second but this is enough to cause its discoverer to predict that a Jupiter-sized planet is orbiting, with the pulsar, about a common center of mass.

Stephen Dole, an American physicist, has predicted that 6 percent of all stars roughly the size of the sun have habitable planets. While astronomers can predict the presence of planets by these indirect means, we likely will never know if we have neighbors in the universe.

FOCUS ON THE PLANETS

August offers little to planet watchers with only Saturn still conspicuous in the evening sky. Skywatchers will have to content themselves with memories of the glory days of July when Venus, Mars, Jupiter, and Mercury gathered together in the west.

SATURN reached opposition in July and is now low in the southeast where it makes a low trajectory across the sky and sets before dawn.

JUPITER is behind the sun and will remain out of sight until the very end of the month when it reappears in the predawn sky.

VENUS and MERCURY will be lost in the sun’s glare as the month begins. Both planets undergo inferior conjunction, i.e. they pass directly between the Earth and sun around Aug. 23 and then reappear on the predawn eastern horizon where the brightness of Venus will make them noticeable.

MARS, now very faint, is on the western horizon during evening twilight near the constellation of Leo.

URANUS and NEPTUNE are hiding in the Teapot asterism of the constellation of Sagittarius. According to Alan MacDonald’s Celestial Calendar, Uranus and Neptune appear closer together this year than they have ever been seen. Uranus was discovered in 1781 but in 1821, the date of their last conjunction, Neptune would not be discovered for another 25 years.

PLUTO is situated in the southwest near the constellation of Libra.

FOCUS ON A CONSTELLATION

High on the northeastern horizon lies the constellation of Perseus the Hero. The 10-star constellation represents Perseus holding aloft the head of Medusa, the Gorgon of Greek mythology, whose hair consisted of writhing snakes and whose visage could turn a person to stone. Perseus got around this difficulty by using a highly polished shield as a mirror while he slew the monster.

The constellation’s major star is Algol, a variable that changes its brightness on a regular basis of every three days. The reason is that Algol is the visible half of a binary system and has an invisible companion that eclipses it every three days for a period of 18 minutes. During the eclipse, Algol is a faint three-magnitude but quickly returns to second-magnitude for another three days after the mysterious companion passes. Each year the Perseid meteor shower originates out of Perseus and promises a good display this year. Watch for it around mid-month.

AUGUST EVENTS

1. Sunrise, 5:21 a.m.; sunset, 8:02 p.m. Lammas, a cross-quarter day.

3. Moon in last quarter, 7:25 a.m.

9. New Moon, 10:27 p.m. Remember, a new moon is always at conjunction, i.e. between the Earth and sun and cannot be seen because of the glare.

10. Sun enters the constellation of Leo the Lion.

12. The Perseid meteor shower peaks around this date. The International Meteor Organization reported 32,041 sightings in 1988 from 157 observers and this should prove to be the major shower of the year.

17. Jupiter is in conjunction with the sun and passes from the evening into the morning sky.

22. The Earth, Venus, Mercury, the sun, and Jupiter form an almost straight line in space tonight.

23. Sun enters the astrological sign of Virgo but is still in Leo astrologically.

25. Full Moon, 5:07 a.m. The full moon of August is called the Green Corn Moon or Grain Moon.

31. Sunrise, 5:56 a.m.; sunset, 7:15 p.m.

Clair Wood, a science instructor at Eastern Maine Technical College, is the NEWS science columnist.