September 2019

September 05, 2019 Posted by: Rich Fefferman, Sky Ranger

As we move to late summer, the planet Jupiter is by far the brightest star-like object in the night sky, in the south to southwest as the sky gets dark.  Saturn, dimmer but still obvious, is the next bright “star” to Jupiter’s left.  These two will be the only planets easily seen this month, as the others hover in the same direction as the Sun.

Dominating the actual stars at this time of the year are the three that make up the huge Summer Triangle- Vega, almost overhead early evening; Altair, to the south; and Deneb, to the east.  The only other “first magnitude” star well placed in the early evening would be Arcturus, far away in the western part of the sky.
Vega is the brightest of the three and is relatively nearby at a distance of 25 light years from Earth.  Look closely, and you may decide that it has a decidedly bluish tint, which is more evident if you use binoculars or a telescope.  The bluish color shows that Vega is quite a bit hotter than our Sun- if you light a candle or match, notice how the hottest part of the flame is blue, followed by white, yellow, orange, and red. 

The stars of Lyra, Vega’s constellation, represent the harp played by Orpheus, whose wife Eurydice was bitten by a venomous snake.  In one of the most famous of all myths, Orpheus’ sweet playing of the harp melted the heart of Hades, who agreed to release Eurydice from the underworld, on condition that he not look back.  Unfortunately, Orpheus did look back to make sure Eurydice was still following, and she was snatched away forever.

A close look at Altair will show that it has a bit more white or even yellow in its color, compared with Vega.  Altair is one of the nearer stars to our Sun, just 17 light years away.  The stars of Aquila are relatively dim, but it is possible to make out the outline of an eagle, especially from dark sky locations.  The eagle is supposed to be the one that Zeus sent down to snatch Ganymede away to Mount Olympus, to serve as cup-bearer to the gods.

Last but certainly not least would be Deneb, brightest star in Cygnus, the Swan.  Although it looks noticeably dimmer than Vega or Altair, Deneb still ranks as one of the first magnitude stars of the sky.  Astronomers have found that this appearance is completely deceiving.  Deneb is so far away from us that its distance is actually hard to measure accurately- it may be as much as 3,200 light years away.   The light from Deneb that you see with your eyes left around the time of the end of the Bronze Age of human history.  If Deneb were as close to us as Altair is, it would shine as a point source, about as brightly as a half moon in the sky!

Cygnus is part of several celestial myths, of which my favorite is that of Phaethon, son of Helios, the sun god.  Phaethon begged Dad to be allowed to drive the sun chariot across the sky, just one time.  Against his better judgment, Helios reluctantly agreed, as parents of teenagers can relate to.  All went well for a time, but Phaethon lost control, charring parts of Earth which remain desert to this very day.  Unfortunately, Zeus had to unleash one of this thunderbolts to save the world from utter destruction, and Phaethon’s body fell into the river Eridanus (today a dim winter constellation).  His heartbroken brother Cygnus dived into the river to collect Phaethon’s bones so many times that the gods decided to immortalize Cygnus by placing him into the sky in the form of a swan.

As can be seen from the attached picture, the stars of Cygnus make out a good stick figure of a swan, or even better, the Northern Cross.  The star marking the head of the swan, Albireo, is a colorful binary star, with one yellow and one blue, very striking in telescopes.

Albireo, Jupiter, Saturn, and the Moon can be seen as part of our monthly telescope viewing at the Gateway Arch, scheduled for Saturday September 7, weather permitting.  First, meet Ranger Karen out on the West Entrance Plaza at 6:30 pm and learn about “Animals of the Park,” a family friendly look at some of the wildlife that lives or has lived on the Gateway Arch grounds.  Once skies get darker, St. Louis Astronomical Society volunteers will provide free telescope viewing out on the Plaza until 8:30 pm.  Call 314-655-1708 in the afternoon to check on the weather for the event.

Last updated: September 5, 2019

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