http://www.skyandtelescope.com.au 17ButhowdoesAGISfigureoutthedistancetostars?Like
anytelescope,Gaia—throughAGIS—cantrackparallax:
thetinyapparentloopingmotionmadebyastaronceayear
that’s caused by the spacecraft’s moving viewpoint around
theSun.However,theloopingmotionsofstarsinthesame
partoftheskywillbesynchronised,makingitimpossible
todeciphertheirtruedistance—onlytheirparallaxrelative
to one another can be calculated. Gaia gets around this
problembyhavingtwofieldsofviewseparatedbyawide
angle.“Ifstarsarewidelyseparatedonthesky,theirlooping
motionswillbeoutofsync,causingavariationintheir
angularseparationovertheyear,”explainsLindegren.
“That variation contains the additional information needed
todeterminethesizeoftheloopsandhencetheabsolute
parallaxes.”
Byspinninginsuchawaythatbothfieldspassover
thesamestarswithinashorttime,andbyregisteringthe
stars’ positions multiple times
to disentangle a star’s real and
apparent motion, AGIS has all
thedataitneedstochurnoutthe
locations,driftacrossthesky,and
distance of all stars at the same
time,transformingthenightsky
jigsawpuzzleintoaliving3D
projection of the known universe.45°EclipticSunPath of
viewing
directions
over 4 daysPath of spin
axis over 4 daysSkinny, light and cheap
In the future, spinning could hold the key to far more
powerful space telescopes. Technology company Raytheon has
been in discussions with NASA researchers on developing its
Rotating Synthetic Aperture (RSA) concept. “As a professor
of physics said of this technology, ‘If Hubble sees toddler
galaxies and the James Webb Space Telescope will see baby
galaxies, RSA will see embryos,’” explains Raytheon Space
Systems Vice President, Wallis Laughrey. “But the best fit
for the technology by far and away is direct imaging of
exoplanets.”
Curved like a canoe, the primary aperture of the telescope
would spin like a wind turbine while taking a series of
images. These pictures would then be combined using
complex algorithms to produce a crisp final scene.
Although it would have reduced light-gathering power, a
skinny, 20-metre-long RSA could provide the resolution of
a full 20-m telescope at the cost
and mass of an 8-m scope. This is
crucial, because the 6.5-m aperture
of JWST is near the limit of what can
fit into current rocket nose cones.
With NASA’s recent cost cap
of between US$3 billion and US$
billion on future space telescopes,
ideas like RSA will be essential for
pushing the boundaries of space-
based astronomy and delivering new
insights into our dynamic universe. BENJAMIN SKUSE is a science
writer based in Somerset, UK.XMIRROR SPINNING Artist’s concept
of Raytheon’s rotating space telescope.
Depending on mission requirements, the
entire mirror and platform could rotate
together (as shown here), or the mirror
RAYTHEON COMPANYcould spin on its own.
... All the telescope records is where
a star shines in its field of view
at a given point in time.