UMBRAS logo courtesy of Spencer Kimball and Gimp

This site is being revamped. 07-11-07

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.

Telescope and Occulter arrangement with respect to Sun and Target Star

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.