Icy Visitor Makes First Appearance to Inner Solar SystemBy NASA’s Amazing Space reporters October 2013

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IMAGE: NASA, ESA, and the Hubble Heritage Team (STScI/AURA)

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.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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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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Continued, page 4… CREDIT: S. Smith, STScI Graphics

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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?

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.

CREDIT: S. Smith, STScI Graphics

November: Before dawn December: After sunset and around dawnLate December: All night and around dawn

November: Before dawn December: After sunset and around dawnLate December: All night and around dawn

November: Before dawn December: After sunset and around dawnNovember: Before dawn December: After sunset and around dawn

November and December: Before dawnNovember and December: Before dawn

November: Before dawn November: Before dawn

Find out more: HUBBLESITE.ORG/GO/ISON

These are the times, by latitude, when ISON is most likely to be visible. These are the times, by latitude, when ISON is most likely to be visible.

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.

www.nasa.gov

http://amazing-space.stsci.edu

All eyes on ISON

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.

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

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are unpredictable. the sun’s heat

could break up Comet Ison,

making it dimmer than expected.

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.

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.

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/