Astronomers Measure Sun-Like Brightness Changes of the Solar Twin,18 Scorpii (Forwarded)

Lowell Observatory

Contact:
Steele Wotkyns, (928) 233-3232
Jeffrey Hall, (928) 233-3202

For Immediate Release: February 15, 2007

Astronomers Measure Sun-Like Brightness Changes of the Solar Twin, 18
Scorpii

Research Yields New Evidence that the Sun's Recent Brightness Variations
are Typical of Sun-Like Stars

Flagstaff, Ariz. -- For the first time, astronomers have collected and
analyzed a long-term set of activity and brightness measurements of a
"solar twin." A team from Lowell Observatory and Tennessee State
University announce today that the close solar analog, 18 Scorpii,
exhibits brightness changes over the course of its activity cycle that are
nearly identical to the Sun's. This star's activity cycle (the phenomenon
that causes the periodic rise and fall in the number of sunspots on the
Sun) is about seven years long, compared to about 10 years for recent
solar cycles. However, 18 Scorpii exhibits a suite of other
characteristics that are essentially the same as the Sun's. These include
mass, temperature, chemical composition, and luminosity.

"We found that where the Sun's overall brightness varies by typically 0.1
percent over its activity cycle, 18 Sco likewise varies by about 0.09
percent, which is effectively the same," said Jeffrey Hall of Lowell
Observatory. "And just like the Sun, 18 Scorpii gets brighter as it gets
more active."

Using complementary observations from Lowell Observatory's Solar-Stellar
Spectrograph (SSS) and Tennessee State's Automatic Photometric Telescope
(APT) program, the astronomers have measured output from one star that
seems indistinguishable from the Sun in all respects: 18 Scorpii, or HD
146233. Identified as a close solar twin in 1997, 18 Scorpii exhibits
behavior very similar to the Sun's, as well as an activity cycle similar
to the Sun's.

"Since about 1970, solar variations probably account for only a small
fraction of observed global warming," said Wes Lockwood of Lowell
Observatory. "However, earlier in the 20th century and in the
pre-industrial era, natural forces, including solar variations,
undoubtedly induced changes in terrestrial climate, and will continue to
do so in addition to the impact of human activities. What we really want
to know is what is the Sun capable of."

Scientists have only been observing solar variations directly from space
since 1978. To estimate what the Sun may have been doing earlier in human
history, particularly during periods of unusual lulls in its activity such
as the Maunder Minimum of 1645-1715, researchers have used "proxy"
indicators, indirect records of solar variations preserved in the
terrestrial record. (The Maunder Minimum was a time period noted by an
absence of sunspots that coincided with the coldest part of the Little Ice
Age).

One method by proxy involves measuring concentrations of certain isotopes
such as Beryllium 10 or Carbon 14. Changes in the strength of the solar
wind modulate the flux of cosmic rays entering Earth's atmosphere, which
in turn, affects the production rate of these isotopes. By measuring the
changing isotope concentrations in terrestrial core samples, scientists
reconstruct estimates of likely solar activity. Another way to constrain
what the Sun might have done during its activity maxima and minima is to
observe what the most nearly Sun-like stars do as their activity varies.
The current research is the most recent finding as part of this unique
long-term program and is in press in The Astronomical Journal: "The
Sun-Like Activity of the Solar Twin 18 Scorpii."

The spectroscopic observations for this study were obtained with the
Solar-Stellar Spectrograph (SSS), operated at the 1.1-meter John Hall
Telescope at Lowell Observatory's dark sky site near Flagstaff, Arizona.
In regular operation for 12 years, the spectrograph allows observations of
Sun-like stars as well as the Sun itself. Meanwhile, co-investigator
Gregory Henry of Tennessee State University acquired brightness
measurements of 18 Scorpii using an 0.8-meter automatic photometric
telescope (APT) at Fairborn Observatory in southern Arizona's Patagonia
Mountains.

Observations from this study serve as a useful guide in reconstructing the
evolution of solar luminosity, particularly with regard to the Sun's
behavior during its occasional quiescent periods. "We know that the solar
twin 18 Scorpii has luminosity variations remarkably similar to those of
the Sun," said Hall. "We'll now continue to study additional stars,
including some that appear to be in Maunder minimum-like periods, and
study their brightness changes. If we can reach a point where we are
reasonably confident that the brightness variations exhibited by Sun-like
stars really are representative of what the Sun does or doesn't do, we can
place some useful limits on how much the Sun did or didn't vary in recent
centuries or millennia. In turn, that helps constrain how much solar
forcing we can justifiably put into climate models."

The result of this study demonstrates that 18 Scorpii, the one star that
seems to best meet all the criteria of a solar twin, is practically a
solar clone in its brightness variations over the past 10 years. Though
over 270 trillion miles away, 18 Scorpii is providing key insights into
the long-term variability of our own star -- and the magnitude of its
influence on terrestrial climate change.

The National Science Foundation and NASA provided funding for this
project.

About Lowell Observatory

Lowell Observatory is a private, non-profit research institution founded
in 1894 by Percival Lowell. The Observatory has been the site of many
important findings including the discovery of the large recessional
velocities of galaxies by Vesto Slipher in 1912-1914 (a result that led
ultimately to the realization the universe is expanding), and the
discovery of Pluto by Clyde Tombaugh in 1930. Today, Lowell's 19
astronomers use ground-based telescopes around the world, telescopes in
space, and NASA planetary spacecraft to conduct research in diverse areas
of astronomy and planetary science. Lowell Observatory currently has four
research telescopes at its Anderson Mesa dark sky site east of Flagstaff,
Arizona, and is building a 4-meter class research telescope, the Discovery
Channel Telescope, in partnership with Discovery Communications, Inc.

For more information:

* TSU Automated Astronomy Group
http://schwab.tsuniv.edu/
* The Sun Blog -- On the trail of a solar clone
http://www.lowell.edu/users/jch/sunblog/

"Andrew Yee" wrote in message ...
Lowell Observatory

Contact:
Steele Wotkyns, (928) 233-3232
Jeffrey Hall, (928) 233-3202

For Immediate Release: February 15, 2007

Astronomers Measure Sun-Like Brightness Changes of the Solar Twin, 18
Scorpii

More canals on Mars?

Andrew Yee (or somebody else of the same name) wrote thusly in message
:

Lowell Observatory

Contact:
Steele Wotkyns, (928) 233-3232
Jeffrey Hall, (928) 233-3202

For Immediate Release: February 15, 2007

Astronomers Measure Sun-Like Brightness Changes of the Solar Twin, 18
Scorpii

Research Yields New Evidence that the Sun's Recent Brightness Variations
are Typical of Sun-Like Stars

Flagstaff, Ariz. -- For the first time, astronomers have collected and
analyzed a long-term set of activity and brightness measurements of a
"solar twin." A team from Lowell Observatory and Tennessee State
University announce today that the close solar analog, 18 Scorpii,
exhibits brightness changes over the course of its activity cycle that are
nearly identical to the Sun's. This star's activity cycle (the phenomenon
that causes the periodic rise and fall in the number of sunspots on the
Sun) is about seven years long, compared to about 10 years for recent
solar cycles. However, 18 Scorpii exhibits a suite of other
characteristics that are essentially the same as the Sun's. These include
mass, temperature, chemical composition, and luminosity.

Could this 18 Scorpii thingy *be* the Sun, where its apparent distance of
however many zillion light years just happens to be the N-th dimensional
circumference of the universe? What we interpret as a distant star is just
sunlight that has gone right round the cosmos and back to us
--
Terms and conditions apply. Batteries not included. Subject to status.
Contains moderate language. Always read the label. Keep out of children.

Interchange the alphabetic letter groups to reply

In article ,
Prai Jei wrote:

snip

Could this 18 Scorpii thingy *be* the Sun, where its apparent distance of
however many zillion light years just happens to be the N-th dimensional
circumference of the universe? What we interpret as a distant star is just
sunlight that has gone right round the cosmos and back to us

A Sun-like star wouldn't be visible at a distance of even *one* zillion
light-years, even with a powerful telescope.

Seriously, according to Hipparcos data 18 Scorpii is only 14.0 (+/- 0.2)
parsecs away, or about 46 LY (and it's barely visible to the naked eye).
That's 'right in our backyard', more than 500 times closer than the
centre of the Galaxy. "Cosmological" distances are many orders of
magnitude greater.

--
Odysseus