This Echo is READ ONLY !   NO Un-Authorized Messages Please!
 ~~~~~~~~~~~~~~~~~~~~~~~~   ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

IMMEDIATE RELEASE: May 5, 2003
Contact: Dave Dooling
National Solar Observatory
P.O. Box 62
Sunspot, NM 88349
505-437-2294 - dooling{at}nso.edu

Modern solar telescope network's view of Mercury passage will help
students use web to recall historical era

A global network of telescopes designed to watch the Sun's atmosphere
pulsate will be pressed into service on May 7 to help students
recreate early measurements of our solar system.

The telescopes will record the transit of Mercury as it crosses in
front of the Sun. Transits once were the most valued of astronomical
events, a rare chance for astronomers to size up the solar system.
Today it is an opportunity to involve science teachers and students
in studying both the Sun and mathematics.

The observations will be made by the National Solar Observatory's
Global Oscillation Network Group (GONG) telescopes located in
Australia, India, and the Canary Islands.

"We were approached by a French colleague, Professor Michele Gerbaldi
of the Institut d'Astrophysique in Paris, Maitre de Conferences at
the University of Paris-Sud, Orsay," explained Dr. Cliff Toner, the
GONG scientist who is spearheading the transit observations. "She
wanted to redo the work of a French expedition in the late 18th
century to measure the scale of the solar system with modern data of
the transit of Venus, observable next year, the one of Mercury this
year being used as preliminary just as it has been the case in the
18th century. It has tremendous historical value, and it is awesome
what those people were able to accomplish." 

Transits occur when Mercury or Venus passes between Earth and Sun.
The timing is complex and depends on the relative motions of Earth
and the other planet. Mercury transits in May at intervals of 13 and
33 years, and in November at intervals of 7, 13 and 33 years. GONG
observed the last transit of Mercury on Nov. 15, 1999. Venus is less
frequent, only six times in the last four centuries. The last was
1883; the next will be very soon, on June 8, 2004.

In the 17th century, pioneering work by Jeremiah Horrocks (an English
astronomer) and James Gregory (a Scottish astronomer) demonstrated
that the transits could be used to determine the Earth-Sun distance.
In 1716 Sir Edmund Halley published "A new Method of determining the
Parallax of the Sun, or his Distance from the Earth" by using many
observational stations spread over the world. But Halley's own
expedition to the South Atlantic in 1677 to observe the transit of
Mercury came to naught when bad weather in England deprived him of
the other half of the observations. 

Several nations mounted expeditions in 1761 and 1769 to observe the
transits of Venus and produced measures of the Earth-Sun distance.
Using those data, Joseph Jerôme Lalande of France in 1771 calculated
the Earth-Sun distance at 153 million km (95 million miles), just 3.4
million km (2 million miles) off the correct number, 149,597,871 km
(92,750,680 miles). Today, radar ranging to the planets and tracking
of deep space probes have relegated transits to reminders of the
pioneering days of astronomy. 

But GONG's constant watch on the Sun means that we don't have to
mount a special expedition. Three GONG stations will see the 5-hour,
19-minute transit. It starts at 05:12:56 Universal Time (12:13 a.m.
EDT) when Mercury's limb appears to touch the Sun's limb, and ends at
10:31:46 UT (5:13 a.m. EDT) when Mercury clears the Sun. Teide will
see the first 3-1/2 hours (from sunrise), Udaipur, India will see the
entire transit, and Learmonth, Western Australia, will see the last
3-1/2 hours (to sunset). Learmonth and Teide will overlap each other
by almost 2 hours. So while the transit will occur entirely at night
for half the world, people anywhere should be able to see it.

CAUTION: It is exceptionally dangerous to view the Sun without the
right equipment. Blindness or painful, permanent eye damage will
result. 

"While we don't expect the size of the Universe to change as a result
of these measurements" said Dr. John Leibacher, the GONG program
director in Tucson, AZ, "it is an exciting spectacle to watch, and it
is of important practical use to us in establishing the precise
orientation of the images taken with different GONG telescopes around
the world." 

GONG was designed to measure the pulsations of the visible surface of
the Sun's atmosphere as it rings like a bell with millions of
different harmonic notes. These vibrations are our only way of
probing the Sun's interior, just as earthquakes probe Earth's
interior. Six identical GONG stations around the globe monitor the
Sun full time: Big Bear Solar Observatory, Big Bear Lake, Calif.;
Learmonth Solar Observatory, Australia; Udaipur Solar Observatory,
India; Observatorio del Teide, Canary Islands; Cerro Tololo
Interamerican Observatory, Chile; and Mauna Loa Observatory, Hawaii.
Thus, the Sun never sets on GONG, making it uniquely suited to
catching a transit whenever it may occur.

Leibacher explained that software has been developed for the GONG
network computers to extract one image every 15 minutes from each
site as Mercury crosses the Sun and post the image in near real-time
on the GONG web site. Only 25 or so images will be posted for this
quick-look, stop-motion movie of the transit. Toner cautioned that
the real-time connection with Udaipur is new and may experience some
interruptions. The connections with Learmonth and Tiede, though are
working well and the overlap between the two will ensure continuous
coverage. 

Over the next two months, as data tapes arrive from the GONG sites,
the GONG team will prepare an education CD-ROM with raw transit
images taken every minute for a total of more than 300 images.

"We'll provide the raw data from the white-light images, so the
students can learn what is the triangulation method and how to
measure the Earth-Sun distance from planetary transits and be
prepared for the transit of Venus, next year which is the one
allowing a measure of the astronomical unit," Toner explained.
Reproducing the timing aspect of the early experiments may not be
possible because each image will have an integration time of one
minute, too long for making precise contact measurements. The CD-ROM
will include instructions on how to use the images and data.

"This is the first time that we have tried something like this, so
everyone here is pretty excited," said Leibacher, "and it's just a
warm-up for the transit of Venus next year."

---------------------------------------------------------------------
GONG is operated by the National Solar Observatory under contract to
the National Science Foundation.

For additional information on GONG and the 2003 transit of Mercury,
visit: http://gong.nso.edu/mercury_transit03. For a larger image of
the 1999 transit, visit the NOAO Image Gallery.

Editor's note: Historical and technical information on transits is
drawn from the transit pages maintained by Fred Espanak of NASA's
Goddard Space Flight Center:
http://sunearth.gsfc.nasa.gov/eclipse/OH/transit03.html.

Halley's paper on determining the Earth-Sun distance is republished
at
http://sunearth.gsfc.nasa.gov/eclipse/transit/HalleyParallax.html.

 - END OF FILE -
==========

@Message posted automagically by IMTHINGS POST 1.30
---