Saturn meets Venus in evening twilight showdown

Venus (bottom) and Saturn (top) appear above the fog Sunday night Sept. 15 about 65 minutes after sunset. Credit: Bob King

A reader mentioned the other day that I seemed pessimistic about seeing the planet Saturn. You know, he was right. Although our favorite ringed planet has settled into obscurity low in the southwestern sky at dusk, it’s still in the game. I easily saw it with the naked eye last night three fingers (5 degrees) above and left of Venus starting about 40 minutes after sunset.

Saturn swings around Venus this week as it heads towards the western horizon. Venus makes the planet easy to find. Stellarium

Venus was a snap! If you know where to look and your sky is clean and clear, you can easily find the planet when the sun’s still up. But 25 minutes after sunset, it’s already so bright it’s hard to miss.

The moon lights up fog in field north of Duluth Sunday night. Credit: Bob King

Saturn passes closest to Venus this Wednesday Sept. 18 and continues moving west until its retirement from the evening sky later in fall. If you’ve had trouble knowing where to look for the planet, allow Venus to show you the way. Saturn hovers just 3.5 degrees north of Venus on the 18th but will be near it now through Sunday evening. A small telescope will still show the rings with ease.

Lights shining through a tree splay into dozens of separate rays in the fog. Diffraction of light by fog droplets tints the outer parts of the glow reddish-orange. Credit: Bob King

As temperatures dip below the dew point at night, humid air gives rise to fog almost as soon as the sun sets. Last night it filled the nearby fields during twilight and rose and fell in slow waves under a brilliant gibbous moon. Pretty entrancing stuff.

Last night’s gibbous moon made a great backdrop for birdwatching. Credit: Bob King

The moon will be a chubby gibbous again tonight, but get ready for the full Harvest Moon coming later this week. We’ll have more on what makes it so special tomorrow.

I noticed last night while observing the moon through the telescope that the seasonal bird migration is well underway. In just a few minutes of gazing I counted a dozen flapping silhouettes flying past the craters Copernicus, Plato and Tycho. Lots more of these avian lunar transits are in store around the time of full moon for anyone with 15 minutes and a small telescope.

The magic of Harvest Moon birdwatching

The moon provides the perfect backdrop for watching birds migrate at night. Observers with spotting scopes and small telescopes can watch the show anytime the moon is at or near full. Photo illustration: Bob King

Where is the interface between the cosmos and planet Earth? Everywhere. Watching birds fly across the shiny coin of the Harvest Moon last night was but one example.  Every September anyone with a telescope magnifying 30x and up who happens to look at the full moon can’t help but notice the occasional silhouettes of migrating birds fluttering across the moon’s face.

Many birds migrate at night both to conserve energy and avoid predators. Identifying the many warblers, blackbirds, sparrows, vireos, orioles and other species that fly across the moon while we sleep may be next to impossible, but seeing them is easy.  Just for fun, I counted the birds in the five-minute interval between 10:57 and 11:02 p.m. last night while looking at the moon at 76x through my 10-inch telescope. The total came to 16, which multiplied by 12 yielded an hourly count of 192 birds.

The reflection of the Harvest Moon creates a fiery squiggle in Amity Creek last night near Duluth. Photo: Bob King

As you might suspect, most of those birds crossed the moon from north to south (about two-thirds) with the other third traveling either east to west or northeast to southwest. Only one little silhouette flapped back up north in the ‘wrong’ direction. Who knows. Maybe it veered off course to pursue a nighttime snack.

According to the Chipper Woods Bird Observatory, located in Indianapolis, most nighttime migrators begin their flight right after sunset and and continue until about 2 a.m. Peak time is between 11 p.m. and and 1 a.m. Bird typically migrate at altitudes ranging from 1,500 to 5,000 feet, but on some nights, altitudes may range from 6,000 and 9,000 feet. I could tell the high ones from the low ones by their size and sharpness. Nearby birds flew by out of focus, while distant ones were very sharply defined and took longer to cross the moon.

Watching birds pass across the moon is a very pleasant activity and reminiscent of meteor shower watching. At first you see nothing, then blip! a bird (meteor) flies by. You wait another minute and then suddenly two more appear in tandem.  Both activities give you that delicious sense of anticipation of what the next moment might hold.

The best time to watch the nighttime avian exodus is around full moon, when the big, round disk offers an ideal spotlight on the birds’ behavior. It’s a fine sight to see one of Earth’s creatures streak across an alien landscape, and another instance of how a distant celestial body “touches” Earth in unexpected ways.  If you’d like to learn more about birdwatching by moonlight, check out the Chipper Woods webpage.

Take the plunge into that burnin’ ring of fire

Individual dew drops line a blade of grass this morning. Photo: Bob King

Yesterday on a walk in Hawk Ridge Nature Reserve near my home, a flock of migrating nighthawks blew by headed south. I identified them right away by their white wing patches. Birds on the move, cool mornings lavish with dew. I like these hints of fall. Through the telescope last night, the nearly 12-day-old moon served as an illuminated stage for the passage of yet more birds. Over a period of five minutes, I saw some a dozen silhouetted avians zip across the cratered landscape on their way outta here.

Now through September is an ideal time to point your telescope at the waxing moon — especially around full phase — to watch birds migrate at night. We don’t think about it much, but many birds are busy migrating while you and I are out like a light. Hummingbirds, warblers and others not only avoid the heat of day by doing so but are less likely to get nailed by a predator under cover of darkness. To watch the show, all you need is a small telescope and a big moon. Plunk in your low power eyepiece and just wait. I saw my first bird within a minute. They fly by quickly, but since I’m no bird expert, I couldn’t identify the different species. Craters are my forte.

Numerous white rings, splashy bright patches and ray systems are best visible around the time of full moon. Credit: Frank Barrett

Some amateur astronomers scorn gibbous and full moons as worthy of study because they’re too bright, and the landscape is washed out due to the sun shining almost directly above the moon’s surface. When the sun shines from the side, as it does near sunset and sunrise both here and on the moon, everything casts a shadow and shows minute detail. Every bump, wrinkle and hair on a person’s face stands out in glaring detail. But shine a light directly at a person’s face – equivalent to the sun shining squarely over the full or nearly full moon – and shadows and those disturbing wrinkles disappear, lost in a flood of light.

A full moon offers no sense of depth or relief, but does reveal details otherwise invisible at other lunar phases. That includes many small craters which hardly anyone notices during lesser phases, but which are transformed into brilliant rings during the equivalent of lunar high noon.  Last night I lost count of how many of these “hot rings” I saw through the telescope at low power. They’re so brilliant they resemble white flares or fiery white-hot rings of lava. Johnny Cash’s “Ring of Fire” comes to mind.

What you’re seeing is high-angle sunlight reflected off fresher rocks and soils on crater rims and floors or from the tendrils of long rays (splashed rock) surrounding fresher craters. The rays and lighter soils truly shine around the time of full moon. Once you get into seeing these strange lunar lily pads, you’ll be surprised at how alien they look compared to the more familiar peaks and crater holes seen to advantage at other phases.

Proclus crater photographed by astronauts aboard Apollo 15. Credit: NASA

I was particularly struck by the fiery ring of Proclus crater and its peculiar off-center system of rays. Proclus, at 18 miles in diameter, is a young lunar crater, and the brilliance of its rim is clearly the result of fresh rock exposed by impact that has yet to darken under the influence of solar radiation. It contrasts beautifully with the older, surrounding moonscape called Palus Somni or the Marsh of Sleep. The weird forked appearance of the rays suggests that the asteroid that created Proclus struck the moon at an oblique angle.

Several of the brightest craters and their systems of rays (strings of fresh secondary craters formed by rock ejected during the main crater's creation) around the time of full moon include Tycho and its rays, Aristarchus and Proclus. Credit: Frank Barrett

Other brilliant craters and ray systems include Aristarchus (brightest crater on the moon) and Tycho, and there are many more. Like Proclus, they’re relatively fresh craters compared to most. With binoculars you can see all three of the aforementioned as bright spots, while any telescope will show their ring-like forms and feathery rays in far more detail. Between moon and birds, you may find yourself staying at the telescope side later than you thought tonight.