The 1989 Planetary Year

Where can you expect to see the other planets in our solar system during 1989? This guide to the planetary year will tell you.


| January/February 1989



planetary year - Voyager 2 orbiting Neptune

Voyager 2 will photograph Neptune during the 1989 planetary year.


PHOTO: JULIAN BAUM/SCIENCE PHOTO LIBRARY

The planetary year simply refers to the positions of the other eight planets through the course of an Earth year and where you can expect to see them. As the only two major bodies closer to the sun that us, Mercury and Venus have shorter orbital periods and thus come in and out of view as they zip past and circle behind the sun. Mars, Jupiter, Saturn, Uranus, Neptune, and Pluto all have longer orbital periods than Earth and thus come in and out of view as we pass them and circle behind the sun.

Mercury never moves far from the sun in either space or our sky, making it the most difficult to see of the bright planets. But this year Mercury reaches greatest elongation (largest apparent separation) from the sun no less than seven times. On some of those occasions, U.S. viewers will get a chance to see the planet either about 60 to 30 minutes before sunrise or about 30 to 60 minutes after sunset. Mercury's best showing at dusk, low in the west, will occur for a few weeks around May 1; it'll be at its morning-twilight best during the weeks around October 10. Mercury has some rather interesting conjunctions (close meetings) this year, including one with Jupiter before dawn on July 2 and with a bright star and Saturn after sunset in mid-December. But its most remarkable conjunction will be an ultraclose encounter with Mars on August 5; I'll describe that event in the section on Mars.

Venus will spend much of 1989 on the far side of the sun from us. At the beginning of the year, it will be low in the east as morning twilight strengthens, and will pass extremely close to three planets — Uranus, Saturn, and Neptune — in succession (of these, however, only Saturn, which Venus will go by on January 16, will be plainly visible to the naked eye). Venus will reach superior conjunction (position opposite the sun from Earth) on April 4 — interestingly, the same day that Mercury also reaches superior conjunction. After this, Venus will play its role as the evening star, getting gradually higher in the sky throughout the summer and early fall. It'll form a close but low conjunction with Jupiter on May 22, and in July will pass near Mars and the star Regulus. Finally, on November 8, the planet will reach its greatest elongation from the sun. At this time viewers with telescopes will get a view of the planet in a half-moon-like phase. The final month of 1989 will find Venus blazing brilliantly in the evening sky, looking ever larger in telescopes, and setting dramatically sooner after the sun each night. Don't miss the fine moon-Venus pairings after sunset on July 4, October 3 and November 2.

Earth seems holiday-oriented this year, at least in terms of its orbit. Our home world will reach perihelion (the closest point in its orbit to the sun) on New Year's Day, 1989, and will be at aphelion (farthest from the sun) on the Fourth of July.

Mars was as close to Earth last autumn as it has been in a generation, but during the first months of 1989 it will be left far behind by our own speedier planet. In January, Mars will cross constellations from Pisces to Aries and will shine as bright as many of the brightest winter stars. By March, it will have dimmed but will still form a dramatic conjunction with Jupiter in the west after nightfall on the 11th. The red planet will also pair up with Venus low in the west on July 11 and 12.

The real high point for Mars, though, will come after sunset on August 5, when it will be a participant in the closest fully visible conjunction of planets taking place before the year 2020. From our vantage point on Earth, the distance between Mars and Mercury will appear to be less than 1/30th of the moon's diameter. The event will be low enough in twilight to make binoculars and very clear skies desirable for viewing (the naked eye will perceive the two planets as a single point of light). To add icing to this cosmic cake, the star Regulus will be only about a degree away. In fact, three nights earlier, on August 2, Mars, Mercury and Regulus will be joined by the crescent moon, forming a marvelously tight quadruple gathering.





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