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

Planet Watch is the Morrison Planetarium's guide to planetary activity for July through September 2017.

The planet Mercury, image by NASA/JPL


The littlest planet always leads hopeful skywatchers on a merry chase, darting from one side of the Sun to the other and switching off between the early evening and predawn skies every few weeks. At the beginning of July, it is separating from the Sun and entering the evening sky, although this is not a favorable apparition for observers in the northern hemisphere because of the shallow angle of the planets' path against the stars with respect to the horizon keeps Mercury from getting very high above the horizon, even when it reaches greatest eastern elongation on July 30.

Will you be able to see the Moon pass nearby, low in the west just after sunset on the evenings of July 24 and 25, when Mercury and the star Regulus (the heart of Leo the Lion) are close together? As Mercury retreats back toward the Sun, its encounter with the Moon on the 21st will be lost in the glare, and after reaching inferior conjunction on August 26, Mercury crosses back over to the predawn sky. It has a spectacular clustering low in the east with Mars, Venus, and the star Regulus from September 10-16, followed by a morning meeting with the Moon on the 18th.

The planet venus, image by NASA/Caltech/JPL


Continuing as a predawn object, Venus shines brightly in the east just before sunrise, moving from the stars of Taurus the Bull into Gemini the Twins, Cancer the Crab, and finally—by September—Leo the Lion, where it has a close encounter with the bright star Regulus. The waning crescent Moon swings nearby on the mornings of July 20, August 19, and September 17.

The planet Mars, image by NASA


The Red Planet is in the process of moving from the evening into the predawn sky, passing conjunction with the Sun on July 27. It doesn't start peeking out of the morning Sun's glare until about mid-September—just in time for closes passes to Mercury on September 3 (probably washed from view in the twilight) and again on the 16th, and the super-thin Moon on the 18th (possibly also very difficult in the twilight). Keep watching, though, because (heads-up!) you'll notice that Mars is headed for a very close predawn pass to Venus, which takes place in early October.

The planet Jupiter, by NASA


An early-evening object, Jupiter is located in the southwest just after sunset, against the stars of Virgo the Maiden, where it's been since last August and will remain—slowly plodding along—through November. Appearing gradually lower through the season, it will be very low in the southwest by mid-September and poorly-positioned for observing as the Sun slowly moves toward the same part of the sky. The Moon passes near Jupiter on the nights of July 28 and August 25. Their encounter on September 22 will be washed from view by the Sun's glare.

The planet Saturn, by NASA/JPL/Saturn institute


Rising in the southeast just after sunset in July, the Ringed Planet lingers lazily against the stars of Ophiuchus the Serpent-Bearer. By August 1, Saturn appears due south an hour after sunset, and by September 1, it's located in the south-southwest at the same time. Look for the Moon nearby on July 6, August 2, and September 29 and 30.

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Planetarium by Night

Planetarium by Night

Morrison Planetarium is open for Thursday NightLife events, featuring special shows and presentations. 

2017 Pocket Almanac

2017 Pocket Almanac

Download the Morrison Planetarium's 2017 Pocket Almanac to stay up-to-date on eclipses, meteor showers, satellite spottings, and more.

2017 Morrison Planetarium pocket almanac