PROBING THE SUN:
High above Antarctica,
a balloon-borne telescope will gather unprecedented images of solar
NCAR scientists and engineers, working with colleagues in Germany
and Spain, are building a unique telescope that will capture images
of the Sun from a perch high in the atmosphere.
At the heart of what’s known as the Sunrise
project is a lightweight,
1-meter telescope. Borne by a balloon, it will circle Antarctica for
about two weeks at an altitude of approximately 40,000 meters (130,000
feet). Its advanced instrumentation will provide high-resolution images
of the Sun’s outer surface, or photosphere, enabling scientists
to get unprecedented views of small-scale magnetic fields that drive
solar variability and profoundly affect Earth’s atmosphere.
The international team expects to launch the telescope in late 2008.
If the instrument can be recovered intact and funding is available,
it will be launched again the following year to obtain additional images.
“This project will allow us to view features of the Sun that
we’ve never seen before,” says NCAR scientist Bruce Lites,
a principal investigator on the Sunrise project.
Learning about magnetic fields
The Sun is the source of light and energy for life on Earth and
the principal driver of atmospheric motion. Solar disruptions, such
as coronal mass ejections, have profound impacts on our upper atmosphere,
touching off geomagnetic storms that affect sensitive communications
and other systems on Earth. But scientists remain uncertain about the
causes of solar variability and disruptions. They need specialized
instruments to examine the Sun in detail.
NCAR scientists Bruce Lites (left) and Kim Streander,
who are working on the Sunrise project, examine a telescope that
will be used to capture ultraviolet images during a test flight.
(Photo by Carlye Calvin, ©UCAR.)
“The Sunrise telescope will allow us to carry out novel research
programs,” says Wolfgang Schmidt of the University of Freiburg in Germany, a collaborator on the project.
The primary goal of the Sunrise project is to investigate the structure
and dynamics of the Sun’s magnetic field. The magnetic field
fuels solar activity and causes variations in radiation, which may
be a significant factor in long-term changes in
The project also may help scientists glean insights into magnetic fields
in general. The universe contains numerous classes of objects, such
as stars, that are dominated by magnetohydrodynamic and plasma processes,
but only the Sun is close enough to examine in any detail.
“Sunrise will broaden our understanding of the really fundamental
physical processes of the outer atmospheres of stars and the forces
that drive stellar winds,” Lites explains.
Working with international collaborators is vital on such a major project,
Lites adds. “The solar community is not large, so solar physicists
around the world need to work with each other,” he says. “In times of limited funding, it’s
especially important to pool our resources and move forward on really
NCAR staffers, using NSF funding and a grant from NASA, are designing
the gondola and telescope pointing system. They are also working
on the data system and cameras for one of the key instruments, a
polarimetric spectrograph that measures wavelengths in the Sun’s
electromagnetic spectrum and enables scientists to make inferences
about its magnetic field.
Researchers at Germany's Max Planck
Institute for Solar System Research are building the telescope, providing optics and mechanisms for the polarimetric
spectrograph, and designing a filtergraph for high-resolution images
in the visible and ultraviolet spectral ranges. Their colleagues at the Kiepenheuer Institute for Solar Physics are creating a fine-pointing system to achieve very high precision image stability. Spanish researchers
at the Astrophysics Institute of the Canary Islands are designing an
imaging magnetograph experiment, which will provide two-dimensional
The telescope is being developed at a time when an array of sophisticated
new solar instruments is coming on line. Images from the 1-meter Swedish
Solar Telescope in the Canary Islands, for example, have been dazzling
the scientific community by showing, for the first time, the three-dimensional
structure of the Sun’s photosphere, as well as
small sunspots that traverse what appear to be raised ridges.
As detailed as these images are, Sunrise will provide far more information,
including measurements of the magnetic fields, in part because the
telescope will reach an altitude at which it will not have to contend
with distortions caused by Earth’s atmosphere.
The balloon-mounted telescope is expected to capture images as small
as 40 kilometers (25 miles), compared to 90 kilometers (56 miles) for the Swedish
telescope. In addition, Sunrise will train its instruments on the same
small area of the Sun for two weeks, thereby allowing researchers to
witness dynamic changes in magnetic fields.
Only in the last few years have scientists discovered planets
orbiting other stars. NCAR’s Timothy Brown, one of
the pioneers in this field, was part of the research team
that, in 2001, made the first detection of a planetary atmosphere
in another solar system. The breakthrough observation pointed
the way toward finding atmospheres hundreds of light years
away and possibly locating planets with similar characteristics
TrES-1, the first extrasolar
planet found by a new small-telescope network, orbits
its bright star in this artist’s rendition. (Illustration by David A. Aguilar, Harvard-Smithsonian Center for Astrophysics.)
Now Brown is working with scientists in the United States
and Spain in a systematic effort to find other planets in
the Milky Way. The project, called Transatlantic Exoplanet
Survey (TrES), utilizes small telescopes in the Canary Islands,
Arizona, and California to scan promising regions of the
galaxy that are crowded with stars. Researchers at NCAR,
the Lowell Observatory, the California Institute of Technology,
and Spain’s Astrophysics Institute of the Canary Islands look for the telltale dimming of starlight that could indicate
an orbiting planet passing between its star and Earth.
Using telescopes on two continents allows the scientists
to focus on the same region for about twice as much time
each night as they could using just one telescope. The effort
began paying dividends in 2004 when the team found a dense,
Jupiter-sized planet about 500 light years from Earth. They
called it TrES-1.
Such research can provide insights into the nature of the
galaxy, the physics of stars (including the Sun), and, perhaps
most intriguingly, whether Earth is an anomaly. “People
like to know how they fit into the universe,” Brown
says. “Is Earth typical, or is it rare or
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