Download 2016-0620-Mountain-Skies

PISGAH
ASTRONOMICAL
RESEARCH
INSTITUTE
Text by Dr. Bob Hayward
Astronomer/Educator
Graphic by TheSky
Software Bisque
Mountain Skies
June 20, 2016
SUMMER BEGINS TODAY
The Earth: Today is the first day of summer! At least this evening is. At 6:34 p.m. EDT today
we have the summer solstice which marks the first moment of summer in the northern hemisphere.
This is the point in the Earth’s orbit when the northern hemisphere reaches its maximum tilt towards the
sun. Thus, the sun is highest in the sky at noon and the days are longest. In Brevard sunrise was at
6:17 a.m. EDT this morning and sunset will occur at 8:49 p.m. this evening. This gives us 14 hours 32
minutes of daytime. The sun rose at 6:15 a.m. in Asheville giving those folks two more minutes of
daylight. Happy Solstice!
The planets: The planets and the moon circle our sky along a path that goes through twelve
very famous constellations and one not so famous (Ophiuchus). As we look at the planets in the sky,
we notice that they are
not scattered all about
but lie close to being
in
a
straight
line
across the heavens.
This is because the
solar system is pretty
much a plane and,
when we look at this
plane
from
our
vantage point inside it,
it looks like a line that
traces a circle around us. This invisible line is called the ecliptic. It is apparent in tonight’s sky as we
see from west to east the planets Jupiter, Mars and Saturn and then the moon.
Jupiter is the brightest of the planets up tonight. (Venus is brighter but is now hidden behind
the sun.) As soon as the sky darkens, we’ll find Jupiter just a bit west of due south and high up in the
sky since he is hanging around the hind feet of Leo the lion.
Down and to the east we’ll note Mars at close to its brightest. The red planet was closest to the
earth on May 30 so it is still quite bright and, through a telescope, relatively large. Its reddish-brown
hue is readily apparent when it is this bright. A bit farther to the east and still lower is the ringed planet
Saturn. If you think Jupiter or Mars is spectacular through a telescope, then take a look at Saturn.
Saturn’s beautiful rings are tilted towards us by just over 26 and, at that angle, present a glorious sight.
They also contribute to Saturn’s brightness. Finally, down and to the east of Saturn is the full moon.
So the line goes from west to east from Jupiter to Mars, Saturn and the moon. Venus is behind
the sun so the only one missing is Mercury. Recall that on May 9 Mercury transited the sun, i.e.,
passed directly in front of it as it moved from the evening to morning skies. So, now Mercury is very
low in the morning twilight before sunrise.
The stars: In the last column we described Boötes the herdsman or bear driver, perhaps better
visualized as a kite. Boötes, with the bright “ginger-colored” star Arcturus being most prominent, is high
in the south on a June evening an hour or two after sunset. Now, look to the east of the herdsman for
an almost complete circle of moderately bright stars that marks the location of Corona Borealis, the
Northern Crown. Then, to the east of the crown, a pattern of six stars forms a great letter “H” in the sky.
Appropriately, this is the constellation of Hercules (known as Heracles to the Greeks). One cannot
study Greek mythology without hearing of the labors of Hercules and many of these stories are
illustrated among the constellations in the sky.
Hercules is pictured upside down as we view him from the northern hemisphere. Thus, the
lower two stars in the letter “H” mark his shoulders, the middle two his waist, and the upper two his
legs. In some ways the constellation is similar to that of Orion the hunter but by no means as obvious.
Perhaps of most interest is the Great Cluster in Hercules, also known as Messier 13 (M13). It can be
spotted with a pair of binoculars or a small telescope on the upper western leg of the letter “H.”
Celestial Calendar:
June 20 - The sun appears to move from Taurus into Gemini.
June 20, 7:02 a.m. EDT – Full Moon
June 20, 6:34 p.m. EDT - Summer Solstice, Summer begins! Longest day of the year
June 27, 2:19 p.m. EDT – Last Quarter Moon
July 4, 7:01 a.m. EDT – New Moon
July 4, Noon EDT - Earth at aphelion (farthest point from the sun)
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PARI is a public not-for-profit public foundation established in 1998. Located in the Pisgah Forest
southwest of Asheville, NC, PARI offers educational programs at all levels, from K-12 through post-graduate
research. For more information about PARI and its programs, visit www.pari.edu. Follow PARI on Twitter at
http://twitter.com/Astronomy_PARI. “Like” PARI on Facebook at
www.facebook.com/Pisgah.Astronomical.Research.Institute.
For further information or questions about this Mountain Skies column, contact Dr. Bob Hayward at
[email protected]. Graphic produced by the author with TheSky Astronomical Software, Software Bisque.