Sky ArchiveTonight

Moon, Jupiter, Saturn September 5 to 7

These next several evenings – September 5, 6 and 7, 2019 – feature the moon and the solar system’s two largest gas giant planets, Jupiter and Saturn. Given clear skies, you can’t miss the moon and Jupiter. The moon is the second-brightest celestial object, after the sun; Jupiter ranks as the fourth-brightest, after the planet Venus, which is in the sun’s glare this month. With Venus gone from our sky, there’s no way to mistake Venus for Jupiter in September 2019. Jupiter is simply the brightest starlike object visible.

You’ll also find a reddish star shining close to Jupiter on the sky’s dome. It’s Antares, the brightest star in the constellation Scorpius the Scorpion. Although Antares provides a prime example of a 1st-magnitude star, it nonetheless pales next to Jupiter. Jupiter, which is brighter than any star, is nearly 20 times brighter than Antares.

Red star with orbit of Mars inside it, smaller red star, sun as tiny white.
Contrasting the supergiant red star Antares with the giant star Arcturus and our sun. Image credit: Wikipedia

As viewed from the mainland United States, the moon reaches its first quarter phase on September 5, 2019, at 11:10 p.m. EDT, 10:10 p.m. CDT, 9:10 p.m. MDT and 8:10 p.m. PDT. By Universal Time (UTC), the moon reaches its first quarter phase on September 6, 2019, at 3:10 UTC. At first quarter, the one half of the moon is illuminated in sunshine while the dark half is engulfed in the moon’s own shadow.

The dark side of a waxing moon always points eastward (direction of sunrise). And the moon in its orbit always travels toward the east, too, relative to the sky background. The moon travels about 1/2 degree eastward – its own width on our sky’s dome – every hour. So the moon will go past Jupiter, and then it’ll go past Saturn.

The moon will swing 2 degrees (4 moon-diameters) to the north of Jupiter on September 6, 2019, at 6:52 UTC. Then the moon (more precisely: the center of the moon) will sweep 0.04 degree to the south of Saturn on September 8, 2019, at 13:53 UTC. In other words, if you’re at the right spot on Earth (Australia and Indonesia) you can actually watch the moon occult (cover over) Saturn on the night of September 8-9. We talk more about this occultation on our post for September 7.

A telescope, even a modest backyard variety, works like a charm for viewing the moon, Jupiter and Saturn. Dust off that telescope and zoom in to scan the lunar terrain, the four major moons of Jupiter and Saturn’s rings.

Take a gander at the moon along the lunar terminator – the shadow line that divides the lunar day from the lunar night. The long shadows along the terminator provide a wondrous three-dimensional portrayal of the lunar mountains, craters and valleys. Believe it or not, this is one time that a dark sky is not an advantage. The glare of the moon is too overwhelming at nighttime, so enjoy your moon watching adventure in a twilight or daytime sky.

Jupiter’s four major moons – Io, Europa, Ganymede and Callisto – are quite easy to see in a low-powered telescope, usually appearing as pinpoints of light along the same plane. Sometimes, a moon or two might not be visible, because these Jovian moons regularly pass behind and in front of Jupiter.

Large fuzzy white dot with tiny bright dots to left and right.
Jupiter and its moons as seen through a telescope on August 15, 2009. Visit Sky & Telescope’s Jupiter moon calculator for the present position of Jupiter’s four major moons.

Click here to find out the positions of these Galilean moons for right now or some chosen time, via Sky and Telescope.

Last but hardly least, aim your telescope at Saturn to see this planet’s glorious rings, which circle Saturn above this planet’s equator. Fortunately, Saturn’s rings are inclined at around 25 degrees in Earth’s sky, so they are quite easy to see in 2019. There are years (2009, 2025) when Saturn’s rings are not inclined at all, but appear edge-on in Earth’s sky. At those times, the rings become invisible. But not this year, because we enjoy a favorable inclination of the rings in 2019.

Viewing Saturn’s rings? Read me first

Small fuzzier photo of Saturn with rings above larger less fuzzy photo.
These images suggest how the ringed planet Saturn might look when seen through a telescope with an aperture 4 inches (100 mm) in diameter (top) and through a larger instrument with an 8-inch aperture (bottom). Image via Space Telescope.

Best of all, we can enjoy observing the lunar landscape, Jupiter’s moons and Saturn’s rings in a sky that’s beset with moonlight or light pollution. These solar system wonders don’t demand the dark sky that far-off galaxies and nebula do.

Bottom line: On September 5, 6 and 7, 2019, use the moon to find the planets Jupiter and Saturn. Have a telescope? Then use it to view Jupiter’s four major moons and Saturn’s glorious rings.

September 5, 2019
Sky Archive

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Bruce McClure

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