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September guide to the bright planets

Jupiter and Saturn are evening planets. Venus, Mercury and Mars are morning planets. Watch for the close conjunction of Mercury and Mars around mid-September.

The waning crescent moon and the dazzling planet Venus adorn the predawn/dawn sky on September 17 and 18. Read more.

Two of the five bright planets – Jupiter and Saturn – appear in the evening sky in September 2017. Meanwhile, the other three bright planets – Venus, Mars and Mercury – all adorn the September morning sky. Bright Jupiter is the first “star” to pop into view at dusk, but follows the sun beneath the horizon at very early evening, especially as viewed from northerly latitudes. Golden Saturn is highest up at nightfall and stays out until late night. Brilliant Venus rises before the sun and helps to guide your eye to the two less-prominent morning planets, Mars and Mercury, with Mercury being the brighter of these two worlds. Rather faint Mars is climbing out of the glare of sunrise all month long. It’ll likely become visible in the morning sky around mid-September 2017. Follow the links below to learn more about the planets in September 2017.

Jupiter brightest “star” in evening sky

Saturn out from dusk until late night

Venus, brilliant in east at morning dawn

Mars climbs out of the glare of sunrise

Mercury, below Venus, visible before sunrise

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Watch for the waxing crescent moon – called a young moon – to join up with the planet Jupiter after sunset on September 21 and 22, 2017. Read more.

Jupiter brightest “star” in evening sky. We passed between the sun and Jupiter on April 7, bringing Jupiter to a point in our sky called opposition by astronomers. Thus Jupiter shone at its brightest and best in April, and yet, even now, it’s still brightest starlike object in your evening sky! Overall, Jupiter beams as the fourth-brightest celestial body, after the sun, moon and Venus. In September, Jupiter shines in the sunset direction at dusk and evening; meanwhile, Venus appears only in the sunrise direction before sunup.

Don’t tarry when looking for Jupiter, especially at northerly latitudes. From the Northern Hemisphere, Jupiter appears low in the southwest to west as darkness falls; from the Southern Hemisphere, Jupiter appears higher up in the sky after sunset. From all of Earth, though, Jupiter sinks in a westerly direction throughout the evening, as Earth spins under the sky. In early September, at mid-northern latitudes, Jupiter sets in the west around nightfall (about one and one-half hours after sunset); and by the month’s end, Jupiter sets before nightfall (roughly an hour after sundown).

Jupiter stays out longer after sunset at more southerly latitudes. At temperate latitudes in the Southern Hemisphere, Jupiter sets in the west at mid-evening in early September, and around nightfall by the month’s end.

Click here for an almanac telling you Jupiter’s setting time and Venus’ rising time in your sky.

From both the Northern and Southern Hemispheres, Jupiter will disappear from the evening sky in October 2017. Look for the king planet to reappear in the morning sky in November 2017. Then a wonderful event will occur! Be sure to watch for Jupiter to join up with Venus to stage a close conjunction in the morning sky on November 13. The sky’s brightest and second-brightest planet near each other will be amazing!

Watch for the moon to join up with Jupiter for a few days, on September 21 and September 22. See the above sky chart. Another wonderful sight! These evenings will be your last chance to see the moon and Jupiter together in the evening sky for many months to come.

Jupiter shines in front of the constellation Virgo, near Virgo’s sole 1st-magnitude star, called Spica. Spica will also disappear from the evening sky in October but you might be able to catch this star near Venus in early November.

Fernando Roquel Torres in Caguas, Puerto Rico captured Jupiter, the Great Red Spot (GRS) and all 4 of its largest moons – the Galilean satellites – on the date of Jupiter’s 2017 opposition (April 7).

If you have binoculars or a telescope, it’s fairly easy to see Jupiter’s four major moons, which look like pinpricks of light all on or near the same plane. They are often called the Galilean moons to honor Galileo, who discovered these great Jovian moons in 1610. In their order from Jupiter, these moons are Io, Europa, Ganymede and Callisto.

These moons orbit Jupiter around the Jovian equator. In cycles of six years, we view Jupiter’s equator edge-on. So, in 2015, we were able to view a number of mutual events involving Jupiter’s moons, through high-powered telescopes. Starting in late 2016, Jupiter’s axis began tilting enough toward the sun and Earth so that the farthest of these four moons, Callisto, has not been passing in front of Jupiter or behind Jupiter, as seen from our vantage point. This will continue for a period of about three years, during which time Callisto is perpetually visible to those with telescopes, alternately swinging above and below Jupiter as seen from Earth.

Click here for a Jupiter’s moons almanac, courtesy of skyandtelescope.com.

James Martin in Albuquerque, New Mexico caught this wonderful photo of Saturn on its June 15, 2017 opposition.

Let the moon guide your eye to the planet Saturn and the star Antares on September 25, 26 and 27, 2017. Read more.

Saturn out from dusk until late night. Look for Saturn as soon as darkness falls. It’s in the south to southwest sky at dusk or nightfall as seen from Earth’s Northern Hemisphere, and high overhead at early evening as viewed from the Southern Hemisphere. Your best view of Saturn, from either the Northern or Southern Hemisphere, is around nightfall because that’s when Saturn is highest up for the night.

Although Saturn has dimmed slightly since August, this world will still be shining at first-magnitude brightness all through September.

Be sure to let the moon guide you to Saturn (and the nearby star Antares) for several days, centered on or near September 26.

Saturn, the farthest world that you can easily view with the eye alone, appears golden in color. It shines with a steady light.

Binoculars don’t reveal Saturn’s gorgeous rings, by the way, although binoculars will enhance Saturn’s color. To see the rings, you need a small telescope. A telescope will also reveal one or more of Saturn’s many moons, most notably Titan.

Saturn’s rings are inclined at 27o from edge-on, exhibiting their northern face. In October 2017, the rings open most widely for this year, displaying a maximum inclination.

As with so much in space (and on Earth), the appearance of Saturn’s rings from Earth is cyclical. In the year 2025, the rings will appear edge-on as seen from Earth. After that, we’ll begin to see the south side of Saturn’s rings, to increase to a maximum inclination of 27o by May 2032.

Click here for recommended almanacs; they can help you know when the planets rise, transit and set in your sky.

Jenney Disimon in Sabah, Borneo captured Venus before dawn.

The waning crescent moon and the planet Venus will be spectacular before sunrise on September 17 and 18. Read more.

Venus, brilliant in east at morning dawn Venus is always brilliant and beautiful, the brightest celestial body to light up our sky besides the sun and moon. If you’re an early bird, you can count on Venus to be your morning companion until nearly the end of 2017.

Venus reached a milestone as the morning “star” when it swung out to its greatest elongation from the sun on June 3, 2017. At this juncture, Venus was farthest from the sun on our sky’s dome, and the telescope showed Venus as half-illuminated in sunshine, like a first quarter moon. For the rest of the year, Venus will wax toward full phase.

Click here to know Venus’s present phase, remembering to select Venus as your object of interest.

Enjoy the picturesque display of the waning crescent moon and Venus in the eastern sky before sunrise on September 17 and September 18.

From mid-northern latitudes (U.S. and Europe), Venus rises about two and one-half hours before the sun in early September, and about two hours before sunrise by the month’s end.

At temperate latitudes in the Southern Hemisphere (Australia and South Africa), Venus rises about one and one-half hours before sunup in early September. By the month’s end, that’ll taper to about one hour.

Click here for an almanac giving rising times of Venus in your sky.

The chart below helps to illustrate why we sometimes see Venus in the evening, and sometimes before dawn.

Earth's and Venus' orbits

The Earth and Venus orbit the sun counterclockwise as seen from earthly north. When Venus is to the east (left) of the Earth-sun line, we see Venus as an evening “star” in the west after sunset. After Venus reaches its inferior conjunction, Venus then moves to the west (right) of the Earth-sun line, appearing as a morning “star” in the east before sunrise.

Mars, Mercury, Earth’s moon and the dwarf planet Ceres. Mars is smaller than Earth, but bigger than our moon. Image via NASA/JPL-Caltech/UCLA.

Before sunrise on September 16, 2017, draw an imaginary line from the waning crescent moon through the dazzling planet Venus to find the planets Mercury and Mars in conjunction near the horizon. Binoculars may come in handy! Read more.

Mars climbs out of the glare of sunrise. Mars transitioned out of the evening sky and into the morning sky on July 27, 2017, at which juncture Mars was on the far side of the sun at what astronomers call superior conjunction.

Look for Mars to emerge in the east before dawn around mid-September or October 2017. The conjunction of Mars and Venus on October 5, 2017, will likely present the first view of Mars in the morning sky for many skywatchers.

Exactly one year after Mars’s superior conjunction on July 27, 2017, Mars will swing to opposition on July 27, 2018. This will be Mars’s best opposition since the historically close opposition on August 28, 2003. In fact, Mars will become the fourth-brightest heavenly body to light up the sky in July 2018, after the sun, moon and the planet Venus. It’s not often that Mars outshines Jupiter, normally the fourth-brightest celestial object.

Wow! Wonderful shot of Mercury – over the Chilean Andes – January 2017, from Yuri Beletsky Nightscapes.

Before sunrise on September 16, 2017, draw an imaginary line from the waning crescent moon through the dazzling planet Venus to find the planets Mercury and Mars in conjunction near the horizon. Binoculars may come in handy! Read more.

Mercury, below Venus, visible before sunrise. When we say Mercury is visible in the morning sky sky, we’re really talking about the Northern Hemisphere. The Northern Hemisphere enjoys a more favorable morning apparition of Mercury in September 2017, but this planet still might be visible before sunrise in the middle part of September from the Southern Hemisphere.

Mercury is tricky. If you look too soon, Mercury will still be under the horizon; if you look too late, it will be obscured by the morning twilight. Watch for Mercury low in the sky, and near the sunrise point on the horizon, being mindful of Mercury’s rising time.

Mercury will be a morning object all month long. Seek for Mercury (and the star Regulus) beneath Venus on September 10, and then let the moon and Venus help guide your eye to Mercury (and possibly Mars) on September 16. In the next few days following the Mercury/Mars conjunction, watch for the moon to swing quite close to Mercury (and Mars) on the mornings of September 17 and 18, as shown on the chart below.

The waning crescent moon and the planet Venus will be spectacular before sunrise on September 17 and 18. Read more.

What do we mean by bright planet? By bright planet, we mean any solar system planet that is easily visible without an optical aid and that has been watched by our ancestors since time immemorial. In their outward order from the sun, the five bright planets are Mercury, Venus, Mars, Jupiter and Saturn. These planets actually do appear bright in our sky. They are typically as bright as – or brighter than – the brightest stars. Plus, these relatively nearby worlds tend to shine with a steadier light than the distant, twinkling stars. You can spot them, and come to know them as faithful friends, if you try.

From late January, and through mid-February, 5 bright planets were visible at once in the predawn sky. This image is from February 8, 2016.  It's by Eliot Herman in Tucson, Arizona.  View on Flickr.

This image is from February 8, 2016. It shows all 5 bright planets at once. Photo by our friend Eliot Herman in Tucson, Arizona.

Skywatcher, by Predrag Agatonovic.

Skywatcher, by Predrag Agatonovic.

Bottom line: In September 2017, two of the five bright planets appear in the evening sky: Jupiter and Saturn. Venus is found exclusively in the morning sky. Let Venus help guide your eye to the two other morning planets, Mercury and Mars.

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Bruce McClure

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