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
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 money.
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 from twilight.
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 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.