Download Icy Visitor Makes First Appearance to Inner Solar System

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Special Feature
Icy Visitor Makes First Appearance to Inner Solar System
By NASA’s Amazing Space reporters
October 2013
F
or thousands
of years, humans have
recorded sightings
of icy visitors sweeping
across Earth’s skies.
These celestial wanderers are
comets, dusty balls of ice that have
traveled billions of miles from
their frigid home in the outer solar
system. They periodically visit the
inner solar system during their
long, looping journeys around
the Sun. These “dirty snowballs,”
as they are sometimes called, hail
from the Oort Cloud, a swarm
of billions to trillions of comets
that surrounds our solar system.
The most famous comet to
appear in our skies is Halley’s
Comet, which visits the inner
solar system every 76 years. Now,
another comet is making an
appearance, and you just might
have a chance to see it this fall.
IMAGE: NASA, ESA, and the Hubble Heritage Team (STScI/AURA)
Hubble’s view of Comet ISON, May 8, 2013: Hubble captured this image of
ISON as it passed between the orbits of Mars and Jupiter at 48,000 miles per hour.
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www.nasa.gov
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Comet ISON’s
grand entrance
Comet ISON is making its first
voyage into the inner solar system,
and has traveled for about 5
million years from its home in
the Oort Cloud. Officially named
Comet C/2012 S1, it has been
nicknamed for the organization
of its discoverers. ISON stands
for the International Scientific
Optical Network, a group of
observatories in ten countries who
have organized to detect, monitor,
and track objects in space.
Astronomers have been tracking
the comet with many telescopes,
including the Earth-orbiting Hubble
Space Telescope, since it was
first detected in September 2012.
Hubble has made a number of
observations of Comet ISON over
the past several months, examining
its size and the structure of the
surrounding cloud of gas, called
the “coma.” The coma consists of
ices evaporated from the surface of
the comet, which are then pushed
back by the solar wind into a tail.
Calling all comet watchers
Beginning in late October, sky
watchers might not need a
professional telescope to view
the comet. Comet ISON may
become bright enough to be seen
with binoculars or a backyard
telescope. Through November,
the time to view the comet is in
the morning before sunrise.
The first weeks of December should
be the best show, if the comet
survives its very close approach to
the Sun on November 28. Comets
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CREDIT: S. Smith, STScI Graphics
Hubble’s view of Comet ISON, April 30, 2013
The Sun-approaching
Comet ISON floats
against a seemingly infinite
backdrop of numerous
galaxies and a handful
of foreground stars. The
Hubble telescope captured
this view on April 30, 2013.
IMAGE: NASA, ESA, and the Hubble Heritage Team (STScI/AURA)
When can I see Comet ISON?
These
These are
are the
the times,
times, by
by latitude,
latitude, when
when ISON
ISON is
is most
most likely
likely to
to be
be visible.
visible.
November:
November: Before
Before dawn
dawn
December:
December: After
After sunset
sunset and
and around
around dawn
dawn
Late
Late December:
December: All
All night
night and
and around
around dawn
dawn
November:
November: Before
Before dawn
dawn
December:
After
sunset
December: After sunset and
and around
around dawn
dawn
November
November and
and December:
December: Before
Before dawn
dawn
November:
November: Before
Before dawn
dawn
In the morning, before
dawn, look in the eastern
sky, near the rising Sun.
In December, when the
comet is visible in the
evening, look in the
western sky, near the
setting Sun.
Find out more: HUBBLESITE.ORG/GO/ISON
CREDIT: S. Smith, STScI Graphics
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are unpredictable. The Sun’s heat
could break up Comet ISON,
making it dimmer than expected.
All eyes on ISON
If the comet survives its brush
with the Sun, it could develop a
long tail and brighten to the point
where it can be seen by the unaided
eye. In December, the comet will
appear in both the early morning
and early evening in the northern
hemisphere, but it will rise with the
Sun in the southern hemisphere.
After that, it will start fading fast as
it travels farther away from Earth.
Observatories, such as Hubble,
will continue to take images of
the comet. Hubble will observe
Comet ISON again during October.
Astronomers are using Hubble
to study the comet’s icy nucleus,
shrouded deep within the gaseous
coma. Based on Hubble images,
astronomers have estimated that
the nucleus is only three or four
miles across. The size is important,
as a larger comet is more likely to
survive its close passage by the Sun.
Comets visible to the human
eye are rare. The most recent
naked-eye comet was Comet
McNaught in 2007, largely visible
in the southern hemisphere.
Of course, many other telescopes
around the world will be watching
as well. In fact, during early
October, the viewing will literally
be “out of this world.” NASA
missions at Mars will be looking
as Comet ISON sweeps past the
red planet. More than a dozen
NASA missions, both at Earth
and Mars, will join the observing
campaign, adding to the data
from thousands of ground-based
telescopes. What would really be
nice is if billions of human eyes
can join the viewing as well.
To find out more about Comet
ISON, check out the ISON blog:
http://hubblesite.org/hubble_
discoveries/comet_ison/
SEE MORE Hubble images and read more
Star Witness news stories at Amazing Space,
NASA’s award-winning educational website
for K–12 students and teachers.
http://amazing-space.stsci.edu
www.nasa.gov