Keeble Observatory
June 2006 Sky from the Keeble Observatory
How big is the solar system? To get a sense of its scale, let’s
compare to some familiar objects. Imagine, first, that Earth was
the size of a basketball. Our Moon would then be roughly the size
of a baseball some 30 feet away. The Sun is 100 times the size of
the Earth-basketball and 400 times farther than the Moon, so think
of a giant (100’ diameter) hot air balloon two and a quarter
miles away. Let’s “re-scale” so we don’t
have to walk so far – let the basketball represent the Sun,
then Earth becomes a 3 mm ball bearing a mere 120 feet away, with
the Moon less than a millimeter in diameter a little over 3½
inches from the Earth-bearing. Jupiter would be a ping-pong ball
600 feet from the basketball Sun; ringed Saturn a little smaller
but twice as far away, its rings represented by a miniature CD.
Let’s call the distance from Sun to Earth an Astronomical
Unit (1 AU). Jupiter lies at about 5.2 AU, Saturn at 10 AU. Far
Pluto is almost 40 AU – almost a mile on this scale. The distant
Oort Cloud, reservoir of long period comets is a thousand times
farther.
Humankind’s most distant ambassadors to the cosmos are approaching
one of the physical boundaries of the Solar System, the so called
“termination shock” where the solar wind plows into
the interstellar medium. The solar wind is a stream of fast moving
ions, which effectively tries to “blow a bubble” in
interstellar space. When the solar wind slows to supersonic speeds
it creates a standing shock wave. Voyager 1 and Voyager 2, both
launched in 1977 and which long ago returned images and data from
Jupiter, Saturn, Uranus, and Neptune (only Voyager 2 for these last
two planets) have been moving outward towards the termination shock
ever since. In 2003, we told you about Voyager 1 encountering the
termination shock, some 85 AU from the Sun. Now Voyager 2 is returning
data suggesting that it, too, has approached that boundary at about
76 AU – suggesting that the “heliosphere” is not
spherical, but bulges outward in the “northern” hemisphere
and is compressed inward to the south. Voyager 1 is currently about
8.7 billion miles from the Sun, traveling at 3.6 AU per year. Voyager
2 is 6.5 billion miles out, traveling at a leisurely 3.3 AU per
year.
Lunar phases for June: First Quarter on the 3rd, at 7:06 pm; Full
Moon at 2:03 pm, on the 11th; Last Quarter on the 18th, at 10:08
am; New Moon on the 25th, at 12:05 pm.
Predawn planet watchers will have to settle for Venus, which will
be brilliant about 20 degrees above the eastern horizon. It will
drift a bit to the north as the month advances.
Evening planet watchers will have more choices. Jupiter begins
at dusk about 25 degrees above the southeast horizon. It sets several
hours after midnight. To the west at sunset, the first planets to
emerge from twilight will be Mercury, Mars, and Saturn. Mercury
begins the month low (about 15 degrees from the horizon) but moves
higher as we get later in the month, reaching greatest eastern elongation
on the 20th. Saturn and Mars are higher, beginning the month several
degrees apart, but rapidly closing to about half a degree separation
on the 17th. Binoculars will also show the open Beehive Cluster
in the same field of view.
Our overhead view at midmonth, about two hours after sunset, finds
little in the way of bright stars directly overhead. However, let’s
take a tour of the brighter stars and constellations closer to the
horizon. To the north, we can find the rather faint Ursa Minor (Little
Dipper). The familiar shape is as thought he dipper is hanging from
its bowl (or standing precariously on its handle), with the end
of the handle at Polaris, the “north star.” Just to
the northwest, we find the brighter and more familiar Big Dipper
of Ursa Major, apparently hanging from its handle. Turning to the
west, we find the familiar sickle of Leo, with its brightest star
Regulus. To the southwest, we find Spica in the constellation Virgo
– virtually the only bright star in that asterism, familiar
in name only because it’s one of the constellations of the
zodiac. Jupiter is much brighter and a bit to the left. That bright
red star to the south-southeast is Antares (“against Mars”)
in Scorpio. Very low to the southeast lies the constellation Sagittarius,
marking the direction towards the center of our Galaxy. If you get
a rare clear and haze free night, binoculars will show this to be
a very rich field, with many bright clusters. To the east and northeast
we find the so-called “summer triangle.” Bright Vega
is high to the east-northeast, with Deneb in Cygnus below and a
bit to the left. To the right, more nearly due east, is Altair.
This grouping will climb higher into the evening sky as summer advances.
Speaking of summer, the solstice will take place on the 21st, when
the Sun reaches its furthest northern point at 8:26 am. This marks
the beginning of “astronomical summer” even though the
daylight hours will begin to get shorter.
For your own monthly star chart, you can direct your web browser
to http://www.skymaps.com.
You will find extensive descriptions of what's worth looking for,
and you can download and print a single copy for your personal use.
Copyright 2006
George Spagna