Step outside around 8:30 p.m. local daylight time on Friday evening (Aug. 28) and Saturday (Aug. 29) and in a single glance you’ll be able to partake in a gathering of the moon and the two gas giants of the solar system in the south-southeast sky.
On Friday, assuming your skies are reasonably clear, you’ll be able to see the moon passing near to the largest planet in the solar system: Jupiter. About one hour after the sun sets, the eye-catching celestial duo will be visible, roughly one-quarter up from the horizon to the point directly overhead (called the zenith).
The moon, which will be just over three days past first-quarter phase — nearly 83% illuminated by the sun — will be situated to the lower right of Jupiter, a distance of roughly 2.25 degrees. That’s equal to about 4.5 times the apparent size of the moon, and that means you should be able to fit at least four full moons in the gap between them in Friday’s evening sky. And yet when you see them in the sky, they’ll be seemingly much closer together because the moon appears twice as big in apparent size to our eyes compared to what its 0.5-degree size would otherwise suggest.
Then there is the other planet, Saturn. But unlike Jupiter there really isn’t anything visually distinctive about it in the evening sky.
It appears as a bright “star” shining with a steady, sedate yellow-white glow, but compared to Jupiter it really isn’t as eye-catching. During this summer, many have had their attention called up to the sky by the appearance of these two “stars,” one dazzling white and the other noticeably dimmer and glowing with a yellowish tinge. If Jupiter were considered to be a “General,” then Saturn might be considered Jupiter’s “Lieutenant.” It shines only 1/14 as bright.
An Illusion of perspective
Many who are just starting out in astronomy likely have passed over Saturn without knowing exactly what it is. If you are among this group then be sure to gaze skyward on Friday. It will be nine degrees to the left of the moon. Your clenched fist held at arm’s length is equal to roughly 10 degrees in width. So, on Friday evening, Saturn will be found nearly one fist to the left of the moon.
Keep in mind that what you’ll be seeing on Friday evening is all a matter of perspective. Saturn is 856 million miles (1.38 billion kilometers) from Earth. Jupiter is 410 million miles (659 million km) away, while the moon is only 238,000 miles (382,900 km) distant. As a result, the moon appears to move much faster (its own diameter per hour) against the starry background compared to the two planets.
But on Friday and Saturday nights, they will be aligned as seen from our Earthly perspective to make them appear as eye-catching sights in our sky
And as a result of its more rapid movement, on Saturday evening, the moon will have shifted away to the east and will be positioned 5.5-degrees to Saturn’s lower left.
Binoculars and telescopes tell the tale
Now properly identified, if you have a telescope or high-power binoculars, make sure to train it on Saturn. Ironically, for a bright planet that appears the least “showy” compared to the others with the naked eye, telescopically Saturn with its magnificent ring system just might be the most spectacular of all!
Any telescope magnifying more than 25-power will readily show them; you might even catch a glimpse of them through image-stabilized high-power binoculars. Saturn’s rings consist of billions of particles ranging in size from sand grains to flying mountains, which are made of or covered by water ice. This would account for their very high reflectivity. Right now, the north side of the rings are tilted 21.5 degrees toward Earth.
In a telescope, Jupiter is also a prime attraction; best observed during early evening when it’s still high and its image reasonably calm. And its four bright moons are always performing. They seem like small stars, though two of them are really larger than our own moon. It’s indeed possible to watch them change their positions relative to each other from hour to hour and from night to night.
In fact, if you look at Jupiter with a small telescope or even steadily held binoculars on Friday evening, you’ll see all four of those big satellites. On one side of Jupiter will be Io and Ganymede (closest to Jupiter) while on the other side you’ll be able to see Europa and Callisto (farthest from Jupiter). On Saturday night, all four satellites will be aligned on one side of Jupiter in this order moving out from the big planet: Io, Europa, Ganymede and Callisto.
And if clouds hide your view of Jupiter, Saturn and the moon, you’ll have another chance to see them gather together again on Sept. 24-25.
Incredibly close pairing!
Jupiter and Saturn are widely separated at the present time — eight degrees to be exact. But in the coming weeks, that wide gap is going to noticeably close and as we get deep into the fall season, you’ll be able to notice the change on a nightly basis.
Jupiter takes approximately 12 years to circle the sun, as opposed to 29.5 years for Saturn. As a result, Jupiter’s normal eastward motion among the stars is considerably faster than that of Saturn and at roughly 20-year intervals it will appear to overtake Saturn in the sky. When Jupiter passes Saturn, it is called a “Great Conjunction.”
Usually, the two planets don’t get much closer than a degree or two apart, but this year will be unusually special. On Dec. 21 — the first night of winter — the two planets will be separated by only one-tenth of a degree, the closest that they have come since 1623.
Let’s all hope skies are clear that night!