This site is being revamped.
 07-11-07
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What is UMBRAS?
UMBRAS is an acronym describing what external occulters do
(Umbral Missions Blocking Radiating Astronomical Sources).
External occultation of starlight is a technique and a class of space science
missions for direct observation of planets around
other stars. 'Direct observation' means images, photometry, and
spectroscopy, as contrasted to the measurement of stellar reflex motion and
variations in starlight flux used to demonstrate the discovery of extrasolar
planets found so far.
External occulter concepts variously discussed and proposed
for decades use a companion spacecraft with a space telescope placed far
from Earth. The companion spacecraft carries an occulting screen
designed to reduce the glare from a star so that a search for planets
may be conducted around it. The utility of this technique is that it
could enable telescopes to take pictures of extrasolar stellar systems
which show planets next to their stars and moving around or with
them through space. More than just interesting pictures, the system
would enable spectra of these extrasolar planet surfaces and atmospheres
in order to determine
their composition and state of rotation.
The not-to-scale artists conception simply shows the relative
arrangement of telescope and occulter: This view is
slightly sunward and perspective-angled from the target star-occulter-telescope
line looking back at the occulting vehicle and
telescope. The star is behind and to the left of the viewer, while the sun is above.
The occulter is placed between
target star and telescope blocking the starlight. This allows
fainter objects to be viewed near the star around the edge of
the occulter. The rectangular screen shape is only the simplest of possible screen shapes
and is not optimal for most science missions. The blue ring-shaped region is
wherein the occulter could be positioned with respect to the sun
(above the viewer) and telescope.
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07-11-07
