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-- WITH PHOTO -- TO NATIONAL, SCIENCE, AND TECHNOLOGY EDITORS:
NASA's Hubble Extends Stellar Tape Measure 10 Times Farther Into Space
WASHINGTON, April 10, 2014 /PRNewswire-USNewswire/ -- Using NASA's
Hubble Space Telescope, astronomers now can precisely measure the
distance of stars up to 10,000 light-years away -- 10 times farther
than previously possible.
Astronomers have developed yet another novel way to use the
24-year-old space telescope by employing a technique called spatial
scanning, which dramatically improves Hubble's accuracy for making
angular measurements. The technique, when applied to the age-old
method for gauging distances called astronomical parallax, extends
Hubble's tape measure 10 times farther into space.
"This new capability is expected to yield new insight into the nature
of dark energy, a mysterious component of space that is pushing the
universe apart at an ever-faster rate," said Noble laureate Adam Riess
of the Space Telescope Science Institute (STScI) in Baltimore, Md.
Parallax, a trigonometric technique, is the most reliable method for
making astronomical distance measurements, and a practice long
employed by land surveyors here on Earth. The diameter of Earth's
orbit is the base of a triangle and the star is the apex where the
triangle's sides meet. The lengths of the sides are calculated by
accurately measuring the three angles of the resulting triangle.
Astronomical parallax works reliably well for stars within a few
hundred light-years of Earth. For example, measurements of the
distance to Alpha Centauri, the star system closest to our sun, vary
only by one arc second. This variance in distance is equal to the
apparent width of a dime seen from two miles away.
Stars farther out have much smaller angles of apparent back-and-forth
motion that are extremely difficult to measure. Astronomers have
pushed to extend the parallax yardstick ever deeper into our galaxy by
measuring smaller angles more accurately.
This new long-range precision was proven when scientists successfully
used Hubble to measure the distance of a special class of bright stars
called Cepheid variables, approximately 7,500 light-years away in the
northern constellation Auriga. The technique worked so well, they are
now using Hubble to measure the distances of other far-flung Cepheids.
Such measurements will be used to provide firmer footing for the
so-called cosmic "distance ladder." This ladder's "bottom rung" is
built on measurements to Cepheid variable stars that, because of their
known brightness, have been used for more than a century to gauge the
size of the observable universe. They are the first step in
calibrating far more distant extra-galactic milepost markers such as
Type Ia supernovae.
Riess and the Johns Hopkins University in Baltimore, Md., in
collaboration with Stefano Casertano of STScI, developed a technique
to use Hubble to make measurements as small as five-billionths of a
degree.
To make a distance measurement, two exposures of the target Cepheid
star were taken six months apart, when Earth was on opposite sides of
the sun. A very subtle shift in the star's position was measured to an
accuracy of 1/1,000 the width of a single image pixel in Hubble's Wide
Field Camera 3, which has 16.8 megapixels total. A third exposure was
taken after another six months to allow for the team to subtract the
effects of the subtle space motion of stars, with additional exposures
used to remove other sources of error.
Riess shares the 2011 Nobel Prize in Physics with another team for his
leadership in the 1998 discovery the expansion rate of the universe is
accelerating -- a phenomenon widely attributed to a mysterious,
unexplained dark energy filling the universe. This new high-precision
distance measurement technique is enabling Riess to gauge just how
much the universe is stretching. His goal is to refine estimates of
the universe's expansion rate to the point where dark energy can be
better characterized.
The Hubble Space Telescope is a project of international cooperation
between NASA and the European Space Agency. NASA's Goddard Space
Flight Center in Greenbelt, Md., manages the telescope. STScI conducts
Hubble science operations. STScI is operated for NASA by the
Association of Universities for Research in Astronomy, Inc., in
Washington.
For images and more information about Hubble, visit:
Logo - http://photos.prnewswire.com/prnh/20081007/38461LOGO
SOURCE NASA
-0- 04/10/2014
/CONTACT: J.D. Harrington, Headquarters, Washington, 202-358-5241, j.d.harrington@nasa.gov; Ray Villard, Space Science Telescope Institute, Baltimore, Md., 410-338-4493 / 410-338-4514, Villard@stsci.edu
/Photo: http://photos.prnewswire.com/prnh/20081007/38461LOGO
PRN Photo Desk photodesk@prnewswire.com
/Web Site: http://www.nasa.gov
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