Solar system showing relative size of (but not distance between) planets.

Keep tabs on our planets with Morrison Planetarium's quarterly guide to planetary activity.


The planet Mercury, image by NASA/JPL

Setting 1-1/2 hours after the Sun on July 1, the smallest of the planets reaches greatest eastern elongation on July 11, when its angular separation east of the Sun is greatest, at 26 degrees. Then, it gradually retreats back into the twilight at about the end of July. Passing inferior conjunction on August 8, when it's between Earth and the Sun, it re-emerges in the predawn sky about a week later, and rises before the Sun, reaching a greatest western elongation of 18 degrees on August 26 (we explain why eastern and western elongations are different in Notes for the Season). After the 26th, Mercury scoots back into the Sun's glow, disappearing from view in early September, and reaches superior conjunction (passing behind the Sun) on September 20. For more on a remarkable planetary sight in July, see Notes for the Season.

The razor-thin Moon can perhaps be seen near Mercury on the evening of July 14, but its encounter on the morning of August 10 is too close to the Sun to be visible, as might their meeting on the morning of September 9.



The planet venus, image by NASA/Caltech/JPL

Venus continues to dominate the early evening sky, shining brightly in the west after sunset and setting 2-1/2 hours after the Sun on July 1, two hours after on August 1, and 1-1/2  hours after on September 1. On the night of July 9, it's only about a degree of arc (twice the apparent diameter of a full Moon) from the star Regulus (the heart of Leo the Lion). Venus reaches greatest eastern elongation on August 17, when its angular separation from the Sun is greatest, at 46 degrees. About a month later, due to a combination of phase and apparent diameter, Venus attains greatest brilliancy on September 25. However, because of the shallow angle of the ecliptic with respect to the horizon, Venus remains fairly low in the sky during this time, at only about eight degrees above the horizon at sunset. On the other hand, when Venus is at its brightest and you know exactly where to look, it's possible to spot it in the daytime with a good pair of binoculars. Of course, if you're going to try this, be careful to not look directly at the Sun at any time—try just after sunset, when the sky is still bright but the Sun is safely below the horizon.

Look for the waxing crescent Moon near Venus on the evenings of July 15, August 14, and September 12.



The planet Mars, image by NASA

At the beginning of July, the Red Planet rises against the stars of Capricornus the Sea-Goat around 10 – 10:30 pm. It rises about four minutes earlier each successive night. Mars reaches opposition on July 26, when it's opposite the Sun in the sky and rises at sunset. This is when it's on the same side of Earth as the Sun and therefore closest to us. At about 36 million miles, it will shine like a bright, orange ember in the night sky, briefly outshining Jupiter (but not Venus). For more on this opposition, see Notes for the Season.

Look for the Moon nearby on the nights of July 26 and 27, August 22, and September 19.



The planet Jupiter, by NASA

At the beginning of July, the largest of the planets is due south at sunset and is already visible against the stars of Libra the Scales, two degrees from the brightest star in that constellation, Alpha Librae. This star is also known as Zubenelgenubi, which means "southern claw," hearkening back to the original interpretation of Libra as the claws of Scorpius the Scorpion. Jupiter's closeness to this star will help you track its slow movement as it slowly moves closer during July and early August, passing half a degree from it on August 14, then continuing eastward after that. Descending toward the western horizon during the evening, Jupiter sets around 2:30 am on July 1, around 12:30 am on August 1, and at about 10:30 pm on September 1.

The Moon passes nearby on July 20, August 16, and September 13.



The planet Saturn, by NASA/JPL/Saturn institute

Having reached opposition at the end of June, the Ringed Planet is low in the southeast at nightfall, just above the lid of the "teapot" asterism in Sagittarius the Archer. The slowest-moving of the naked-eye planets, it changes its location against the stars by all of 2-1/2 degrees during the course of the season. Basically moving with the stars, then, it rises about four minutes earlier each successive night and is seen in the south-southeast just after sunset at the beginning of August and due south after sunset at the beginning of September. Only slightly past opposition, Saturn is ideally positioned for viewing through telescopes, through which its bright rings and perhaps a few of its larger moons are visible.

Look for the Moon near Saturn on the nights of July 24, August 20, and September 16 and 17.