The 1982 Planetary Fandango
In a previous column , it was pointed out that while the planetary alignment this spring posed no danger by creating the so-called "Jupiter Effect," the phenomenon would indeed provide a spectacular sight for star-gazers.
Three bright planets--Mars, Jupiter and Saturn--will be more compactly gathered in the southern sky this summer than at any other time until spring of the year 2000. Unfortunately, the time of closest gathering will occur in July when the northern sky is light all night, but late winter and early spring will provide views nearly as good. To add window dressing to the occasion, the bright star Spica in the constellation Virgo adds a fourth member to the assemblage. Spica is a blue giant 220 light-years from the earth (by contrast, the sun is 8 light-minutes from the earth).
On February 23, Mars approaches to within less than 3° of Saturn, and then appears to back away from it. In fact, from that date until early summer, all three planets are in retrograde motion as seen from the earth. This means that Earth, being closer to the sun with a shorter orbital period and faster velocity overtakes and passes the other three planets like a race car on the inside lane. Hence, those planets in the outside lanes appear to move backward against the backdrop of the stars. By midsummer, the earth has placed enough distance between itself and the other planets that they are again seen to move slowly across the sky from right to left in their forward or "direct" motion.
The December 1981 issue of Sky and Telescope magazine gives further information relating to events pictured in the top figure of the accompanying graphics. On March 30, Mars is at opposition (on the opposite side of the earth from the sun) and will be due south at midnight. On May 11, Mars ends its retrograde motion and begins to move eastward again. The close approaches of Mars to Saturn and Spica on July 6 and 22 will probably be difficult to see during the northern summer, but on August 7 Mars passes only 2° from Jupiter before going rapidly eastward. By mid-September the array of planets has spread out again, and Spica and Saturn will soon disappear into the sun's glare.
It would be difficult to miss this grouping in the night skies of early spring, but it is helpful to bear in mind that the planets are always found along the ecliptic--the same path through the sky that the sun takes during the day. During late February, Spica and the three nearby planets will be low in the southern sky at about 3 a.m.
During part of 1982, all the other five planets will also be in the night sky at once (that is, all on the same side of the sun as the earth), but they are much more spread out and most are invisible to the unaided eye. An exception is Venus, which is at its brightest on February 24 and rises in the southeast two hours before sunrise. At this time Venus will be the brightest object in the sky after the sun and the moon, and can be seen during the daytime if one knows where to look. A good pair of binoculars and a steady rest should resolve the crescent shape of Venus at this point in its orbit. Venus, being in an orbit inside that of the earth's, passes through phases like those of the moon.
