June 2005 Sky from the Keeble Observatory
One of the exciting things about astronomy (actually, I find all
of astronomy exciting!) is that we can plan to write a three-month
series on Einstein to commemorate the 100th anniversary of his so-called
“miracle year,” and then find something so compelling
that plans change. We’ll return to Einstein next month, but
now for some current news:
Humankind’s most distant messenger has passed another milestone.
Voyager 1, launched in 1977 (about the same time as the original
Star Wars!) is now 8.7 billion miles from home, and still returning
scientific data. For perspective, that is nearly twice the distance
from the Sun as Pluto. Originally intended as a probe of Jupiter
and Saturn (its twin, Voyager 2, also flew past Uranus and Neptune),
Voyager appears now to have crossed the “termination shock”
into the “heliosheath” marking the boundary between
our solar system and interstellar space.
What had been expected when this occurred was a sudden decrease
in the speed of the solar wind and a parallel jump in the magnetic
field strength measured in the solar wind. Prior to November Voyager
was measuring solar wind speeds on the order of 1.5 million miles
per hour – they have now fallen well below that and have remained
there. These events seem to have taken place last November, but
some researchers remained skeptical, in part because the termination
shock is expected to expand and contract with changes in the solar
wind, and is likely to be irregular. Voyager’s instruments
also show the heliosheath region to be more turbulent than anticipated.
Voyager 1 is leaving the solar system roughly in the same direction
that the Sun orbits in the plane of the Galaxy. The termination
shock in that direction is similar to the wave pushed in front of
a boat moving through water, or to the layer of snow piling up in
front of a plow. In 1995 the Hubble Space Telescope imaged a similar
bow shock in the vicinity of the star LL Orionis. The shock front
in this image is several light years long, and clearly shows the
star moving left to right through its surrounding gas cloud.
Image courtesy NASA, the Hubble Heritage Team (STScI/AURA)
Voyager 2 is heading out into interstellar space along a different
trajectory, and has not yet reached the termination shock in that
direction. Both spacecraft have sufficient propellant for attitude
control and sufficient electrical power from onboard radioisotope
generators to last another decade or so. Stay tuned, because the
current NASA Administrator has suggested shutting them down to save
For more information, check out the NASA web site at:
Lunar phases for June: Last New Moon at 5:55 pm, on the 6th; First
Quarter on the 14th, at 9:22 pm; Full Moon on the 22nd, at 12:14
am; and Last Quarter on the 28th at 2:23 pm.
The Sun reaches its highest point on the celestial sphere at 2:46
am on the 21st, marking the Summer Solstice. We’re actually
further from the Sun now than in mid-winter, but the high position
above the celestial equator (and above the southern horizon) maximizes
the solar heating of the ground. Southern hemisphere folks are heading
Jupiter is climbing higher into the evening sky as the month passes.
Look for it about 50 degrees above the southern horizon early in
the month, moving further west as we approach July. Saturn is still
lingering near Castor and Pollux in Gemini, getting lower and lower
as we follow the winter constellations into the glare of the setting
Sun. It’s about 40 degrees above the western horizon early
in June. Venus is about halfway between Saturn and the Sun at twilight,
climbing progressively higher from night to night. Saturn and Venus
will be joined by swift Mercury, and on the 24th these three bright
planets will be within a few degrees of one another when they emerge
Predawn planet watchers will have to content themselves with Mars,
which begins the month about 40 degrees above the southeast horizon
at sunrise. It will move to nearly 50 degrees and more toward the
south by the end of June.
At mid-month, an overhead view about 2 hours after sunset still
gives us little to cheer about. Bootes is now the constellation
at zenith, but its rather undistinguished, except for its one truly
bright star, Arcturus, which lies about 20 degrees to the south
of zenith. Following the line from zenith through Arcturus will
bring us to Spica, the brightest star in Virgo, about halfway to
the horizon towards the south-southwest. Turning to the west we
see the familiar sickle of Leo, now turned towards the horizon and
soon to be gone until next winter.
Back to zenith, if we now let our eyes settle toward the eastern
horizon, we’ll see the small square of Hercules above the
much brighter Vega, in Lyra. Below Vega is Deneb in the constellation
Cygnus, which marks the direction of our Sun’s orbit in the
Galaxy. And, as we noted above, this is the general direction towards
our distant probe, Voyager 1.
For your own monthly star chart, you can direct your web browser
You will find extensive descriptions of what's worth looking for,
and you can download and print a single copy for your personal use.