Press release
(National Media)
When Mercury goes in
front of the Sun on Wednesday, a rare event, scientists from Williams College
and the University of Arizona will be observing it from vantage points on
earthbound mountains and with orbiting spacecraft. Jay Pasachoff of
Williams College (Williamstown, Massachusetts) and Glenn Schneider of the
Steward Observatory of the University of Arizona (Tucson, Arizona) will be
perched at the University of Hawaii's solar observatory, at the rim of the
giant Haleakala crater at an altitude of 10,000 feet on the island of
Maui. (The crater is wider than Manhattan island and deeper than
Manhattan's tall skyscrapers.) Separately, Williams College's Bryce
Babcock and solar astronomer Kevin Reardon from the Arcetri Observatory in
Florence, Italy, will observe the transit from the Sacramento Peak Observatory
in Sunspot, New Mexico.
Pasachoff and
Schneider are already experts on such events, which are known as
transits. Among planets, only Mercury and Venus can go in transit across
the face of the Sun, as seen from the Earth, since they are the only planets
whose orbits are inside that of Earth's. Pasachoff and Schneider have
already used the 1999 transit of Mercury to unravel a centuries-old mystery
known as the black-drop effect. (Their analysis was published in the
journal Icarus and in the
proceedings of an International Astronomical Union symposium on the transit of
Venus.) This blurring of the
distinction between a planet's silhouette and the edge of the Sun prevented
accurate knowledge of the size of the solar system for hundreds of years.
It had been seen at the very rare transits of Venus, which occur in pairs
separated by over a century, and often falsely attributed to Venus's
atmosphere. Pasachoff and Schneider, on the other hand, by observing and
explaining a black-drop effect at a transit of Mercury observed from NASA's
TRACE spacecraft, showed that no atmosphere was necessary, since Mercury's
atmosphere is negligible and the spacecraft was outside Earth's atmosphere.
Transits of Mercury
occur a dozen times a century, most recently in 2003. The next won't
occur until 2016. So a small coterie of scientists interested in the Sun
or in the solar system are making careful observations at the 2006 opportunity.
Pasachoff and Schneider, in Hawaii, will work with University of Hawaii
scientists Jeff Kuhn, Don Mickey, and Garry Nitta to observe Mercury's stately
progress silhouetted against the Sun for approximately 5 hours, from 9 am to
just after 2 pm local time (2 pm to sunset Eastern Standard Time). The
whole transit, from beginning to end, will be visible in Hawaii, while only the
first half of the transit will be visible from the eastern United States, the
Sun setting with Mercury's disk still appearing on it.
Pasachoff and
Schneider and their University of Hawaii Institute for Astronomy colleagues
will use the Imaging Vector Magnetograph instrument on the telescope in the
Mees Solar Observatory in a spectral-scanning mode in an attempt to measure the
sodium component of Mercury's extremely tenuous "atmosphere," measure
its height, and determine how it varies from Mercury's pole to its
equator. They will additionally
use the polarimetry capability of the instrument to try to detect the weak
Mercurian magnetic field against that of the Sun.
Pasachoff and
Schneider extended their interest in transits to the 2004 transit of Venus, the
first to be visible from Earth since 1882. They teamed up with Richard
Willson of Columbia University, whose NASA satellite ACRIMSAT is able to
measure the total amount of energy from the Sun that reaches Earth. They
were able to measure a decrease of a tenth of one percent in the radiation from
the Sun because of Venus's blocking the Sun's disk. (They reported their
results in the April 10, 2006, issue of the Astrophysical Journal.) The event provides a close analogy in our solar
system for transits increasingly found for planets around other stars.
NASA's Kepler spacecraft, to be launched in 2008, should discover hundreds of
planets around other stars with this transit technique. Whether
Pasachoff, Schneider, and Willson manage to detect Mercury's silhouette in the
total solar radiation is marginal, since Mercury's silhouette is only 1/25th
the area of Venus's.
Williams College
scientist Bryce Babcock will work with Kevin Reardon of Italy's Arcetri
Observatory (Reardon is a Williams College alumnus) at the Sacramento Peak
Observatory in Sunspot, New Mexico, part of the U.S. National Solar
Observatory. From their 9200-foot altitude, they will use the transit of
Mercury observed at the Dunn Solar Telescope there to measure the true sizes of
the smallest features visible in the solar atmosphere. The availability
of Mercury's sequentially blocking small features on the Sun from its position
outside the Earth's atmosphere will make such observations possible. They
will use camera systems obtained with a grant from NASA for Pasachoff and
Babcock's studies of Pluto and other solar-system objects.
Reardon and Babcock
will use a special instrument known as IBIS, constructed at the Institute in
Florence and installed at the Dunn Solar Telescope, to construct a detailed map
of the sodium atmosphere of Mercury. This experiment is led by Andrew
Potter, currently a visitor at the National Optical Astronomy
Observatories. The team in New Mexico, as well as Pasachoff and
Schneider's team and Kuhn's team in Hawaii, will try to detect the spectrum of
sodium in Mercury's atmosphere as it passes in front of the Sun.
Pasachoff and
Schneider are working with scientists at Lockheed Martin Solar and Astrophysics
Laboratory and at the Harvard-Smithsonian Center for Astrophysics, especially
Leon Golub and Edward Deluca at the latter, to use not only NASA's 8-year-old
Transition Region and Coronal Explorer (TRACE) spacecraft, which they had used
previously, but also the new Hinode spacecraft, launched by the Japanese space
agency on September 22, 2006, carrying telescopes from their Lockheed Martin
and Harvard-Smithsonian collaborators.
Pasachoff's research
about planetary transits is supported by a grant from the Committee on Research
and Exploration of the National Geographic Society. He will be joined on
Maui by Williams undergraduate Suranjit Tilakawardane, a student fron Sri Lanka
who is a senior astronomy major.
From the ground, the
transit of Mercury will not be as visible as 2004's transit of Venus, since
Mercury's disk will be too small to be seen without use of a telescope or
binoculars. But the Sun is so bright that your eyes can be hurt if you
look at it without special solar filters. So only people with access to
solar filters or specially filtered telescopes, or who project the solar image
onto a wall without looking through the telescope, will be able to see the
November 8 event. The whole transit from beginning to end will be visible
in Hawaii and in the extreme western United States. From New Mexico
eastward to the Atlantic, the sun will set with Mercury's disk still
silhouetted against it.
___
contact information:
Pasachoff's cell
phone is 617 285 6351. On the nights of the sixth and seventh of
November, he will be at the Upcountry Bed and Breakfast in Kula, Maui, 808 878
8083. The telephone at the Mees Solar Observatory of the University of
Hawaii, at the Haleakala summit, is 808 243 5892. (Many cell phones do
not work at the summit.)
Jay M. Pasachoff
Field Memorial
Professor of Astronomy
Director, Hopkins
Observatory
Williams College
33 Lab Campus Drive
Williamstown, MA
01267-2565
413 597 2105; fax 413
597 3200
jay.m.pasachoff@williams.edu
Contact information
for Schneider:
Glenn Schneider
Associate Astronomer & Hubble NICMOS Project Instrument
Scientist
Steward Observatory
* Phone: 520-621-5865 fax: 520-621-1891
Dept. of Astronomy * email: gschneider@as.arizona.edu
933 N. Cherry Avenue*
University of Arizona * World Wide Web Information Server (Home
Page URL):
Tucson,
Arizona 85721 * http://nicmosis.as.arizona.edu:8000
Pasachoff Website on
transits of Venus and Mercury: http://www.transitofvenus.info
NASA site from Fred
Espenak with a visibility map and table: http://sunearth.gsfc.nasa.gov/eclipse/OH/transit06.html
See also a Website
from Chuck Bueter at http://www.transitofvenus.org/mercury.htm
Information
about safe observation while looking toward the Sun, using suitable filters or
projection methods, is available from the site of the International
Astronomical Union's Working Group at Eclipses (Pasachoff is Chair)
at www.eclipses.info and www.transitofvenus.org/safety.htm.
Schneider
Websites on transit observations:
http://nicmosis.as.arizona.edu:8000/ECLIPSE_WEB/TRANSIT_04/TRACE/TOV_TRACE.html
http://nicmosis.as.arizona.edu:8000/ECLIPSE_WEB/TRANSIT_04/ACRIMSAT/ACRIMSAT_TOV.html