At mid-northern latitudes, Saturn lords over the evening sky all by himself all month long! And that’s very unusual, because Saturn is the faintest and least noticeable of the bright planets. So why is Saturn top dog at northerly latitudes in September, 2015? Only because Mercury is hiding in the evening twilight for the Northern Hemisphere. Meanwhile, at southerly latitudes, two planets are visible in the evening, as Mercury presents its finest evening apparition of the year. The other three visible planets – Venus, Mars and Jupiter – are in the east before sunrise, with Venus pointing the way to Mars and Jupiter appearing in mid-month in predawn twilight. Follow the links below to learn more about September planets.
Mercury in evening twilight, best from Southern Hemisphere. Mercury is our solar system’s innermost planet and always stays near the sun in our sky. This planet passed out of the morning sky and into the evening sky in July, 2015. It’ll remain an evening object for an unusually long time, until the very end of September, 2015.
It’s a real challenge to catch Mercury from northerly latitudes, however.
For the Southern Hemisphere, September presents Mercury’s best appearance in the evening sky for all 2015. In the first week of September, Mercury sets a whopping two hours after sunset, and the innermost planet’s great evening apparition will continue throughout the most of the month – in the Southern Hemisphere and the northern tropics.
At temperate latitudes in the Southern Hemisphere, this world actually sets after the end of evening twilight till around September 20. Look for Mercury over the sunset point on the horizon as dusk gives way to darkness. Click here for recommended almanacs. They can help you find Mercury’s setting time in your sky, and for the time at which astronomical twilight ends.
Those residing at northerly latitudes aren’t as lucky this month. At mid-northern latitudes in early September, Mercury sets less than one hour after the sun. That’s the best it gets for us in this hemisphere this month. From northerly latitudes, the innermost planet will be hard to catch even with binoculars in the glare of evening dusk. However, binoculars are always recommended to enhance sky views!
Mercury will stay in the evening sky until September 30, 2015. Then it’ll pass into the morning sky, to give the Northern Hemisphere its best morning apparition of Mercury for the year in October.
Saturn easily visible from nightfall until mid-to-late evening. Throughout September 2015, the golden planet Saturn pops into view at nightfall. At northerly latitudes, Saturn sets around mid-evening. At temperate latitudes in the Southern Hemisphere, Saturn sets at late evening or after midnight.
How can you recognize this wonderful planet? It’s golden in color, to the eye. It shines with a steady light. Check the chart above for dates when Saturn will appear near the moon this month. If you can identify Saturn, near the moon, and notice the stars around it, you’ll be able to spot it when the moon has moved away.
Binoculars don’t reveal Saturn’s gorgeous rings, by the way. For that, you need a small telescope. But binoculars will enhance Saturn’s golden color.
Saturn’s rings are inclined at about 24o from edge-on in September 2015, exhibiting their northern face. A few years from now, in October 2017, the rings will open most widely, displaying a maximum inclination of 27o. 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.
Brilliant Venus in the east before sunrise. Here’s a very fun observation to make this month: Venus before dawn. Venus is the brightest planet and third-brightest sky object overall, after the sun and moon. When it’s visible, it’s very, very prominent in our sky.
This month, Venus will exhibit its greatest brilliancy as the morning “star” for approximately one week, centered on September 21, 2015.
But don’t wait until then to spot the queen planet Venus. She’ll be in good view all month long, rising before dawn’s first light.
Moreover, this dazzling world will enable you to locate the fainter yet relatively nearby planet Mars in the morning sky. Be sure to use the waning crescent moon to locate Venus (plus Mars and Jupiter) in the morning sky on September 9, September 10 and September 11.
Mars in vicinity of Venus before sunrise. Mars officially passed into the morning sky on June 14, 2015. Earth and Mars travel in orbit at similar speeds (Earth at 18 miles per second, Mars at 15 miles per second). So it takes awhile for Mars to climb away from the glare of sunrise, and, when it finally does so, Mars tends to linger in the predawn sky. That has been especially the case in the Southern Hemisphere for these last few months.
But now that Venus is returning to the morning sky, Mars will be easier to see in September, 2015. As September progresses, Mars will rise sooner before sunrise and be higher up at dawn. Plus the dazzling planet Venus will be fairly close to Mars throughout the month, and Venus can serve as your guide to the Red Planet.
Bright Jupiter appears in mid-month below Venus and Mars at dawn. Jupiter shines more brilliantly than any star. It’s the second-brightest planet after Venus. Both Venus and Jupiter transitioned over into the morning sky in August, 2015. However, Jupiter lurks much closer to the glare of sunrise than does either Venus or Mars in September, 2015.
Keep watching, though, as Jupiter climbs upward, toward Mars and Venus, in September and October. It should appear in your predawn sky, very low in the east before dawn, around the middle of September. Then keep watching. Jupiter will catch up with Mars on October 17, to exhibit their closest and only conjunction until January 7, 2018.
Jupiter will finally catch up with Venus on October 26, 2015, to stage the year’s third and final conjunction of these two brilliant worlds.
In late June and early July of 2015, when Venus and Jupiter were shining in the evening sky, these two blazing beauties showcased their closest conjunction until August 27, 2016, and displayed a second – though less close – conjunction in the evening sky on July 31 – the same date as this year’s Blue Moon.
Now these two brilliant worlds are heading for their third and final conjunction of the year in the morning sky on October 26, 2015.
By a wonderful coincidence, as Venus and Jupiter show off their final conjunction of the year – on October 26 – Venus will reach its greatest western (morning) elongation from the sun.
Moreover, the year’s closest grouping of three planets – Venus, Mars and Jupiter – will also take place on October 26. That’s a big deal because the next planetary trio won’t occur again until January, 2021!
Normally, if you have binoculars or a telescope, it’s fairly easy to see Jupiter’s four major moons, which look like pinpricks of light 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. In September of 2015, however, Jupiter’s moons will have a hard time competing with the sun’s glare in the morning sky.
These moons circle Jupiter around the Jovian equator. In cycles of six years, we view Jupiter’s equator edge-on. So, in 2015, we get to view a number of mutual events involving Jupiter’s moons through a high-powered telescope. Click here or here or here for more details.
Click here for a Jupiter’s moons almanac, courtesy of Sky & Telescope.
What do we mean by visible planet? By visible 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 visible planets are Mercury, Venus, Mars, Jupiter and Saturn. These planets are visible in our sky because their disks reflect sunlight, and these relatively nearby worlds tend to shine with a steadier light than the distant, twinkling stars. They tend to be bright! You can spot them, and come to know them as faithful friends, if you try.
Bottom line: In September 2015, Saturn can be seen at evening from around the world. Mercury visible at nightfall at southerly latitudes. Venus and Mars east before dawn. Jupiter still obscured in the glow of dawn.