Download september 2013 - Holt Planetarium

FRIENDS OF THE PLANETARIUM NEWSLETTER – SEPTEMBER 2013
Comet ISON, currently on its way in towards the Sun, has been in the news for a different reason lately.
We have nothing to fear from the incoming Comet ISON, no matter how the icy object behaves during its
much-anticipated close approach to the sun this November, scientists say. Comet ISON will miss Earth
by many millions of kilometers during its swing
through the inner solar system; and so will its
bits and pieces if the comet happens to break
apart along the way. While a breakup would be
bad news for skywatchers hoping for a great
show from ISON, which was billed as a "comet
of the century" candidate almost immediately
after its discovery in September 2012, it could
have a silver lining. If a breakup happens, we
may be fortunate enough to witness a beautiful
'string of pearls' in the sky; similar to what
Hubble observed when the comet S-W 3 broke
up in 2006. Scientists think Comet ISON is
making its first trip to the inner solar system
from the Oort Cloud, a repository of trillions of icy bodies thought to lie 1 light-year or so from the sun.
ISON is streaking toward a solar encounter on Nov. 28, when the comet will skim just 1.2 million
kilometers above the sun's surface. If ISON survives that close pass, it could blaze up incredibly brightly
in Earth's night sky, experts say. Skywatchers and scientists alike are keeping a close eye on ISON, trying
to predict just how it will behave over the coming months. Recent observations are not terribly
encouraging and suggest that the comet is not brightening as much as expected or hoped on its trek
toward the sun.
Going in the opposite direction, it appears that the Voyager 1 spacecraft has left our Solar System.
Voyager 1 arrived in interstellar space in
August 2012 after 35 years of spaceflight;
researchers announced on Sept. 12.
While this milestone is momentous
enough in its own right, it also opens up a
new science campaign whose potential
already has scientists salivating. Voyager
1 and its twin, Voyager 2, were launched
a few weeks apart in 1977 to study
Jupiter, Saturn, Uranus and Neptune, as
well as the moons of these outer planets.
The probes completed this historic
"grand tour" in 1989, and then embarked
on a quest to study the outer reaches of
the solar system and beyond. Voyager 1
finally popped free of the heliosphere, the huge bubble of charged particles and magnetic fields that the
sun puffs out around itself, on or around Aug. 25, 2012, becoming humanity's first envoy to the vast
realms between the stars. Voyager 1 reached the boundary of the heliosphere in 2004, a milestone
marked by readings showing the speed of the solar wind had dropped below that of sound but it took
another nine years to complete the crossing and move out into interstellar space. It covers about 1.5
million kilometers per day and is currently 19 billion kilometers from Earth. At that distance, it takes
more than 17 hours for 22-watt radio signals, moving at 300,000 kilometers per second, to cross the
vast distance between the spacecraft and the giant antennas on Earth that are needed to collect the data.
By the time the signals get to Earth, they are a fraction of a billion-billionth of a watt.
Somewhat closer to home, there are planets aplenty in the western evening sky. Venus is the brilliant
evening star. It appears in the west soon after sunset and sets in the southwest after 11 p.m. It is bright
enough to cast shadows. Saturn is directly below Venus at the beginning of October. Below and left of
Saturn is Mercury. Through the first half of October Venus and Mercury hold their positions from night
to night while Saturn sinks lower. On the 7th Saturn will be just below the crescent moon with Mercury
to their left. After the 15th Mercury sinks lower. It is again near Saturn as the two planets fade into the
bright twilight in the last days of October. What is really happening is that we are moving to the far side
of the Sun from Saturn. It is 1620 million kilometers away. Mercury and Venus are catching us up.
Mercury, going fastest, swings out from the far side of the Sun at first, then falls lower in the twilight as
it passes between us and the Sun. It will be closest to us, 101 million kilometers away, on November
2nd. Venus is at maximum swing out from the far side of the sun. It will be 120 million km away mid
month, looking like a tiny first-quarter moon in a telescope. After twilight ends on moonless evenings in
a dark rural sky the Zodiacal Light is visible in the west. It is seen as a faint broad column of light
stretching up the sky to Venus. It is sunlight reflecting off meteoric dust in the plane of the solar system.
The morning sky has its share of planets too. Jupiter rises around 3 a.m. in October. By dawn it is low in
the northern sky. It is brighter than all the morning sky stars and shines with a steady golden light.
Binoculars and small telescopes show Jupiter's brightest moons close to the planet. Jupiter is around
750 million km away from us mid- month. Orange Mars and white Regulus, the brightest star in Leo,
make a close pair low in the northeast dawn around the 15th. Mars is on the far side of the sun, 300
million km away.
It took sharp and patient eyes,
but researcher Mark Showalter
of the SETI Institute has found
a tiny moon orbiting about
100000 kilometers from
Neptune that’s never been
seen before. Showalter used
archival data from the Hubble
Space Telescope to find the
moon, designated S/2004 N 1,
which is estimated to be no
more than 19 km across,
making it the smallest known
moon in the Neptunian system.
This is the 14th known moon
of Neptune and brings grand total of known planetary satellites to 174. Meanwhile, astronomers have
approved official names for the newest and smallest of Pluto's five moons, discovered in Hubble images
taken in 2011 and 2012. Members of the public were offered the opportunity for the first time to vote
on the names chosen. A list of 21 candidate names drawn from mythic underworld realms was posted
on a website. The votes are in, nearly a half million of them, including some 30,000 write-ins, and the
winners are Kerberos (for P4) and Styx (for P5). In Greek mythology, Styx is the river (and the goddess
thereof) that separates Earth from the underworld. Kerberos is the three-headed guard dog that
prevents the dead from escaping the underworld. The IAU picked this spelling over the variant
Cerberus, which is already used for an asteroid.