BACKYARD ASTRONOMY

By Eric Saltmarsh

AUGUST, SEPTEMBER, AND OCTOBER NIGHT SKIES

Late summer and early autumn skies are strewn with planets, with four visible without optical aid.

At the beginning of August, we say goodbye to the planet Mars, as it fades into the sunset glare. Mercury and Venus return to the evening skies in the second part of September, just after sundown.

Jupiter and Saturn are easy naked eye objects near the south, bracketing the summer Milky Way. Uranus and Neptune both reach their closest approaches to Earth, but remain so far away that they can best be seen with optical aid.

Since all the planets (and dwarf planet Pluto) are in our night sky during this period, you might listen to Gustav Holst’s wonderful 1916 symphony, ‘The Planets.’ Mr. Holst really captures the different musical moods of the planets.

As summer turns to fall, we’re well-positioned to observe the Milky Way on clear, moonless nights. Just after dark in mid-September, the Milky Way, or ‘Milky Circle’ to the ancient Greeks, appears as a ribbon of faint, glowing cloud, running from the SSW to NNE horizons, passing overhead.

The Milky Way is the galaxy that our solar system resides within. A galaxy is an enormous group of stars and dust that is gravitationally bound together. In our case, the galaxy is spiral-shaped, since everything is rotating, due to gravitational attraction. However, we can’t see the spiral shape of our galaxy because of our perspective inside the galaxy.

Our Milky Way Galaxy contains 100 billion to 400 billion stars. While not considered huge when compared with the hundreds of billions of other galaxies in the universe, light from one end of the Milky Way takes 150,000 to 200,000 years to cross to the other end.

In mid-September, the center of the Milky Way is low in the SSW, located near the ‘spout’ in Sagittarius. Because we’re peering toward the center of the galaxy, this part of the Milky Way is particularly rich in star clouds, dark lanes of intergalactic dust, nebulae, globular clusters, and open clusters, many visible to the unaided eye and easily resolved in small telescopes.

For example, try to find the globular cluster called Messier 22 (a.k.a., M 22) in Sagittarius. Globular clusters are large groups of stars that were born together and are tightly bound by gravity. While M 22 appears as a fuzzy star to the unaided eye, there are over 80,000 densely packed stars in this cluster.

In contrast, near the tail of Scorpius is an open cluster of stars, known as Ptolemy’s Cluster (a.k.a., M 7). Unlike globular clusters, open clusters are relatively small groups of stars that were born in the same gaseous cloud and are loosely bound by gravity. In this open cluster, you can see individual stars, even with binoculars. There are about 80 stars in Ptolemy’s Cluster.

Above Ptolemy’s Cluster (M 7), you might notice a tiny, fuzzy object that looks a bit like the Beatles’ Yellow Submarine. This is an enormous cloud of interstellar gas where new stars are being born. We know it as the Lagoon Nebula (a.k.a., M 8).

On good viewing nights, you can see the gauzy star clouds of the Milky Way interrupted by dark intrusions that seem relatively free of stars. These dark areas are huge clouds of interstellar dust that block the light of the stars beyond. The main intrusion of dark dust that runs from Sagittarius (near the SSW horizon) to Cygnus (overhead) is known as The Great Rift.

The accompanying photos show just a few of the Milky Way objects we can see without the need for a powerful telescope.

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Here is a summary of night sky events occurring in August through October 2019:

August 9: Mercury is at greatest western elongation in the ENE, visible in the brightening dawn, on the Gemini-Cancer border.

August 12-13: The Perseid meteor shower peaks on the night of the 12th and pre-dawn of the 13th. While upwards of 60 meteors per hours can be expected during the peak, light from the waxing, gibbous moon will interfere with the viewing of faint meteors.

August 15: The full Green Corn moon occurs at 6:30am MDT in Capricornus.

August 30: New moon.

September 10: The planet Neptune will be at opposition to the Sun and visible all night long, appearing as a faint, pale blue star to those with binoculars and telescopes.

September 13: The full Harvest Moon occurs at 10:34pm MDT, near the Aquarius-Pisces border. On this evening, give a listen to the recently deceased Leon Redbone’s rendition of ‘Shine On Harvest Moon.’ R.I.P., Mr. Redbone – I was a big fan.

September 23: The Autumnal Equinox occurs at 1:50am MDT as the Sun crosses the equator into the southern hemisphere, ending summer in northern latitudes.

September 28: New moon.

September 29: Try to pick out the close grouping of Mercury, Venus, and the thin crescent moon, just above the WSW horizon, between 7pm and 7:15pm MDT. You may need binoculars to do so.

October 8-9: The Draconid meteor shower peaks with ten meteors per hours on the night of the 8th and pre-dawn of the 9th. The moon sets at about 3:00am MDT, but by then the shower radiant will be low in the north.

October 13: The full Hunter’s Moon, located in Pisces, occurs at 3:09pm MDT.

October 20: Mercury, in Libra, is at its highest point above the western horizon, just after sunset. Venus is the bright ‘star’ to Mercury’s right.

October 21-22: The Orionid meteor shower peaks on the night of the 21st and early morning of the 22nd. At peak, the shower produces about 20 meteors per hour. A waning crescent moon rises about 2am MDT, but it shouldn’t pose a significant problem to early morning viewing.

October 27: New moon.

October 27: Faint Uranus is opposite the Sun in the sky and visible all night in the constellation Aries. At magnitude 5.7, Uranus will just be visible to the unaided eye in a dark, clear sky, if you know exactly where to look.

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POTENTIAL PHOTOS:

Last year’s Harvest Moon rising. Santa Fe, NM.

The Milky Way above the SSW horizon as it would appear at 10pm MDT in mid-September.

The Milky Way from halfway up the SSW sky to overhead, as seen in mid-September at 10pm MDT.

THE SKY ABOVE THE GRAND CANYON

AUGUST 25 & 26, 2019

General Observation: The sun sets around 7:12pm local time (note: AZ does not recognize daylight savings time).

Darkness will occur around 8:46pm local time.

The waning crescent moon won’t rise until well after midnight, so you should have dark skies for your star party on both nights.

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Milky Way: When darkness falls, the Milky Way will run from the SSW horizon to just east of overhead, then down to the NNE horizon. It starts at the SSW horizon in the constellation Scorpius (the Scorpion), passes through Sagittarius (the Centaur), Scutum (the shield), Aquila (the Eagle), Cygnus (the Swan, a.k.a., the Northern Cross, just east of overhead), then drops through Cassiopeia (the Queen), and Perseus (mythical person from ancient Greece), above the NNE horizon. Viewing the Milky Way over the canyon should be an unforgettable sight.

The Milky Way is brightest in the SSW because, there, you’re looking toward the center of the Milky Way galaxy – the point at which our galaxy appears to rotate. You can’t see the center of the galaxy because of interstellar dust that blocks it, but it’s located in Sagittarius, near the ‘spout.’

The galactic center is so distant that, if you removed the intervening interstellar dust, the light from the center would take approximately 26,500 years to reach us. A giant black hole is at the center of the galaxy. With a mass equivalent to 4.3 million of our suns, the gravitation of the black hole is so strong that nothing can escape from it – not even light.

Please see my Aug-Oct Backyard Astronomy draft article (emailed to you on July 6) for more info on the Milky Way Galaxy, including photos.

Other Interesting Objects in the Sky on August 25-26:

Jupiter: As darkness falls, our solar system’s largest planet, Jupiter, is the brightest object in the sky, located in the constellation Ophiuchus, the Serpent Bearer, in the SSW. Jupiter is called a gas giant planet, due to its enormous atmosphere (mostly hydrogen and helium) and supposed lack of solid surface.

A small telescope can begin to show the colored bands in Jupiter’s atmosphere and its slightly oval shape, both caused by the planet’s fast rotation. You could fit over 1,300 Earths within Jupiter’s volume, yet it spins on its axis in under ten hours (as compared to Earth’s 24-hour rotation).

In one of Jupiter’s belts is a huge storm called The Great Red Spot that is likely to be over three centuries old. This storm is easily seen in small telescopes under favorable viewing conditions, assuming it’s facing Earth.

Currently, Jupiter has 79 known moons. Four of them were discovered by Galileo Galilei, in the early 17th century. These four ‘Galilean Moons’ are easily viewed in a small telescope.

Tonight (Aug 25, 2019 and Aug 20, 2019), Jupiter is approximately 460 million miles from Earth. The light from Jupiter you see, left the planet 42 minutes ago. If the planet exploded 30 minutes ago, you wouldn’t know it for another 12 minutes!

Saturn: The planet Saturn can be found in Sagittarius (the Centaur), on the eastern (left) side of the Milky Way. A gas giant like Jupiter, Saturn appears significantly fainter since it is somewhat smaller than Jupiter and almost twice as far away (875 million miles away from Earth on August 25-26).

Named for the Roman god of agriculture, Saturn displays a beautiful ring system, visible even in small telescopes. Currently, there are 62 known moons. The largest moon, Titan, is the second largest moon in the solar system and the only one known to have a dense atmosphere. Some scientists believe that life may exist on the surface of Titan or within its methane seas. Titan is visible in small telescopes as a tiny dot, assuming it isn’t in front of or behind the planet.

Andromeda Galaxy: About a quarter of the way up the ENE sky is a faint oval patch of light. This is the Andromeda Galaxy, one of our closest galactic neighbors. While faint, you’re seeing the combined of light of one trillion stars.

To give you a sense of scale, the light you see tonight, left the galaxy 2.5 million years ago (on Earth, the earliest fossil of the homo species is only two million years old). Also, light takes over 200,000 years to travel from one end of the Andromeda Galaxy to the other.

In 4.5 billion years, the Andromeda Galaxy is expected to ‘collide’ with the Milky Way Galaxy. However, ‘collide’ is not the best word to describe this event since the two galaxies will likely pass through one another without a single star collision! That’s how big and spread out galaxies are!

Double Cluster in Perseus: About halfway up the northeastern sky, the Double Cluster in the constellation Perseus, can be found without optical aid. The Double Cluster is actually two separate, open clusters within our galaxy. Each cluster contains several hundred stars and are about 7,500 light-years from Earth. While they appear close to one another, they are actually several hundred light-years apart.

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