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From: NASANews@hq.nasa.gov
Date: Fri, 14 Feb 1997 14:43:38 -0500 (EST)
Fwd Date: Sat, 15 Feb 1997 03:07:17 -0500
Subject: Thought-Provoking Imagery Shows Sun's Place in the

Douglas Isbell
Headquarters, Washington, DC             February 14, 1997
(Phone: 202/358-1753)

Public Affairs Office
Naval Research Laboratory, Washington, DC
(Phone: 202/767-2541)

RELEASE:  97-28

THOUGHT-PROVOKING IMAGERY SHOWS SUN'S PLACE IN THE GALAXY

     An action-packed movie assembled from images taken by an
instrument aboard the NASA-European Space Agency Solar
Heliospheric Observatory (SOHO) has provided a remarkable
galactic perspective on the Sun and its place in the Milky Way.

     Taken during Dec. 22-27, 1996, the series of images show
the Sun drifting in front of the stars of the constellation
Sagittarius, as the constant solar wind blows outward in all
directions.  Soon, a comet passes into view from the south
and disappears behind the Sun.  Finally, in an unrelated event,
a plainly visible giant puff of solar gas is emitted, representing
a large mass ejection in a direction away from the Earth.

     The remarkable images come from SOHO's visible-light
coronagraph, LASCO, which is able to mask the intense rays
from the Sun's surface in order to reveal the much fainter
glow of the solar atmosphere, or corona.  Operated with its
widest field of view, LASCO's unprecedented sensitivity
enabled it to see the thin ionized gas of the solar wind out
to the edges of the picture, 13 million miles from the Sun's
surface.  Many stars are brighter than the gas, and they
create the background scene.

     The results may alter human perceptions of the Sun in
the same way that the Apollo lunar mission photographs
revealed the Earth to be a beautiful but isolated planet in
space, according to leader of the LASCO team, Dr. Guenter
Brueckner of the Naval Research Laboratory, Washington, DC.

     "I spend my life examining the Sun, but this movie is a
special thrill," Brueckner said.  "For a moment, I forget the
years of effort that went into creating LASCO and SOHO, and
leave aside the many points of scientific importance in the
images.  I am happy to marvel at a new impression of our busy
star that gives us life, and which affects our environment in
many ways that we are only now beginning to understand."

     For many centuries even astrologers knew that the Sun
was in Sagittarius in December and drifting towards the next
zodiacal constellation, Capricorn.  This was a matter of
calculation only, because the Sun's own brightness prevented
a direct view of the starfield.  The SOHO-LASCO movie makes
this elementary point of astronomy a matter of direct
observation for the first time.

     "This is an especially dramatic sample of the data that
scientists are now starting to gather routinely from SOHO,"
said George Withbroe, director of the Sun-Earth Connection
science program at NASA Headquarters, Washington, DC.  "It
really helps drive home the idea that the Sun is a typical
star, although we certainly have a special relationship with it."

     In the movie, north is at the top of the scene, which
corresponds with the orientation of the Sun as seen at midday
in the northern hemisphere of Earth.  SOHO's progress in
orbit around the Sun remains in step with the Earth's motion.
SOHO travels towards the right (west) in relation to the
stars during the period of observation.  As a result, the
Sun's position appears to shift to the left (eastwards) in
front of the stars.  In this mode, LASCO observes an area of
the sky 32 times wider than the visible Sun itself.

     At the time of the observations, SOHO is looking towards
the heart of the Milky Way Galaxy, which lies in the
constellation of Sagittarius.  The Milky Way, made by the
light of billions of distant stars, forms a luminous band
slanting down and to the right.  Dark lanes seen in the Milky
Way are real features familiar to astronomers. They are
created by dust clouds in the disk of the galaxy that obscure
the distant stars.

     A doomed comet, previously unknown, enters on the left
of the image on Dec. 22. Its path curves towards the Sun and
on Dec. 23 it disappears behind the occulting mask of the
coronagraph.  It fails to reappear on the far side of the
Sun.  Whether or not its trajectory took it directly towards
the visible surface, the comet must have evaporated in Sun's
atmosphere.  It was one of a family of comets known as
sungrazers, believed to be remnants of a large comet that
broke up perhaps 900 years ago.  Other fragments were
responsible for spectacular comet apparitions in 1843, 1882
and 1965.

     Called Comet SOHO 6, it is one of seven sungrazers
discovered so far by LASCO. Analyses of these cometary
orbits, now in progress, are a prerequisite for their
inclusion in the official record of comet discoveries.  LASCO
also provided unique pictures of Comet Hyakutake passing
behind the Sun in early May 1996.

     Debris strewn from the tails of many comets makes a disk
of dust around the Sun, in the ecliptic plane where the
planets orbit. It scatters sunlight and is sometimes visible
attwilight on the Earth, known as the Zodiacal Light.  In the
raw images obtained by LASCO, the Zodiacal Light is brighter
than the solar corona. Image processing subtracted these
effects precisely, to bring the solar wind and the Milky Way
into plain view.

     Random flickers of light in the images are due to cosmic
rays striking the detector. Cosmic rays are energetic
particles coming from exploded stars in the Milky Way, and
variations in the solar wind influence their intensity in the
vicinity of SOHO and the Earth. Operating beyond the Earth's
protective magnetic field, which repels many particles, SOHO
is more exposed to the cosmic rays.

     In the largest outburst from the Sun seen in the
December movie, a mass ejection causes billions of tons of
gas to race out into space on the right-hand (western) side
of the Sun.  The origin of this event much lower in the Sun's
atmosphere was evident in an expanding bubble seen in
processed images from the SOHO extreme ultraviolet imager.

     Coronal mass ejections are the hurricanes of space
weather. SOHO is ideally placed to report and even anticipate
their origins in the Sun's atmosphere. Although the Sun is
supposedly very quiet at present, being close to the minimum
count of sunspots, LASCO has observed so many outbursts large
and small -- roughly one a day -- that scientists are having
to think again about how to define a coronal mass ejection.
Later LASCO images, from Jan. 6, 1997, revealed a large mass
ejection directed towards the Earth.

     The movie and still photographs related to it are
available on the Internet at the Naval Research Laboratory's
SOHO/LASCO home page:

http://lasco-www.nrl.navy.mil/lasco.html

     A mission of international scientific cooperation
between NASA and the European Space Agency (ESA), SOHO was
launched on Dec. 2, 1995.  It is situated near the L-1
Lagrangian point, where the Earth's and Sun's gravitational
forces balance, some one million miles sunward from the
Earth.  This vantage point enables solar astronomers to use
SOHO's 12 science instruments to observe the Sun
continuously, with no intervening "night."  Major areas of
research include studies of the solar interior via
helioseismology, the solar atmosphere in ultraviolet and
visible light, and the solar wind and energetic particles.

     SOHO and its instruments are operated from the Goddard
Space Flight Center, Greenbelt, MD, for the NASA's Office of
Space Science, Washington, DC.

     Brueckner will discuss the video and its contents in
detail in a briefing at 6 p.m. EST on Saturday, Feb. 15,
during the annual meeting of the American Association for the
Advancement of Science at the Seattle Convention Center.  For
more information, contact the AAAS press room at 206/624-9087.

			-end-