Astro Bob: Full Sturgeon Moon aligns with ring king
On Thursday, Aug. 11, the full moon will be in conjunction with Saturn. Watch them sail together across the southern sky.
Though still a day shy of full, the Wednesday, Aug, 10, moon seemed incredibly bright. A clean, haze and smoke-free sky helped, but I think the main reason had to do with the moon's altitude. In August, the full moon climbs higher in the southern sky than it does in June and July.
Altitude makes a difference. A low moon shines through more air because we're looking nearly horizontally through the bottom of the atmosphere. Air density reaches an extreme at the horizon, the reason a rising or setting moon appears much fainter and more colorful than a high one. The color arises because the thick air scatters away every color in moonlight except the warmer, redder hues.
Not only was Wednesday night's moon higher and brighter, it was whiter, too. A full moon always lies 180° opposite the sun. When the sun shines highest in the sky at the time of the June solstice, the moon hunkers down in Sagittarius half a sky away. Better known as the "Teapot," the sun will occupy the same spot on the first day of winter.
In mid-August, seven weeks after the solstice, our daytime star's slow slide from "summit" to "valley" is well underway. In response, the full moon moves higher in the sky, ascending from Sagittarius into Capricornus.
On Thursday night, Aug. 11, it will share that constellation with Saturn. On Aug. 9, during a public stargazing event, we all "oohed" and "aahed" at the planet's rings through the telescope. Even at a magnification of 60x they were bright and clear.
Seeing Saturn reminded me again how deprived our ancestors were of cosmic knowledge about the physical nature and wild variety of the universe. Planets were moving points of light. Craters on the moon? Unknown. Galaxies, nebulas, black holes, exoplanets, globular clusters and yes, Saturn's magnificent rings, essentially didn't exist. Nowadays we can enjoy observing these beauties and more with an instrument you can buy online in 10 minutes.
While Jupiter, Uranus and Neptune are encircled by bands of ice and dust, Saturn's rings are the only ones that don't require a huge instrument or a spacecraft visit to see. A small telescope magnifying 40x will do the job. Not only are they far richer in material than the others, but they're composed of highly reflective water ice and much more extensive.
The major rings extend for 170,000 miles (270,000 kilometers) but are only about 300 feet (91 meters) thick. Appearances otherwise, if you could scrape all the material into a ball, it would be 4,700 less massive than the moon!
So what do you get when you put a fabulous full moon together with the solar system's coolest planet? A conjunction! That's exactly what we'll see Thursday night after the sun sets and twilight mellows into darkness. Look to the southeast early on. You'll spot the moon easy enough, which will rise shortly after sunset for the Americas. To catch it the instant it crests the horizon, check your local sunset time and find a place with an unobstructed view to the east.
The moon will dangle about 4.5° below Saturn, making the planet easy to spot. Three nights later, on Aug. 14, Jupiter will get a visit from the waning gibbous moon. You'll need to stay up a little later for a good look. Both will light up the eastern sky starting around 10:30 p.m. local time.
The moon is a good friend to the planets. Every month, it makes a complete circle around the sky as it orbits the Earth, visiting each of them in turn.