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The Largest Astro
Of All Time . . . 46
A tiny section of the Milky Way showing
Eta Carinae; itself a tiny section of the
46-billion pixel image shown at top of page.
24 Silicon Chip
siliconchip.com.au
nomical Image
BILLION Pixels!
by
Ross Tester
Astronomers at the Ruhr-Universität Bochum in Germany have
compiled the largest astronomical image to date – a picture of the
Milky Way which contains 46 billion pixels. The image contains data
gathered in astronomical observations over a period of five years.
C
alled the Bochum Galactic Disk Survey, they monitored a 6° wide stripe along the southern Galactic disc
simultaneously in the r and i bands, using a robotic
15-cm twin telescope of the Universitätsternwarte Bochum
near Cerro Armazones in Chile. Utilising the telescope’s
2.7° field of view, the survey observed a mosaic of 268 fields
once per month and monitored dedicated fields once per
night. The survey reached a sensitivity from 10m down to
18m (AB system), with a completeness limit of r ~ 15.5m
and i ~ 14.5m which – due to the instrumental pixel size
of 2. 4” – refers to stars separated by >3”.
Five-year observation period at the observatory
For five years, the astronomers from Bochum have been
monitoring our Galaxy in the search of objects with variable
brightness. Those objects may, for example, include stars
in front of which a planet is passing, or multiple systems
where stars orbit each other and which obscure each other
every now and then.
In his PhD thesis, Moritz Hackstein is compiling a catalog of such variable objects of medium brightness. For
this purpose, the team from the Chair of Astrophysics
takes pictures of the southern sky night after night, using
the telescopes at Bochum University’s observatory in the
Atacama Desert, Chile.
More than 50,000 new variable objects, which had hitherto not been recorded in databanks, have been discovered
by the researchers so far.
268 individual images make up
the photo of the Milky Way
The area that the astronomers observe is so large that they
have to subdivide it into 268 sections. They photograph
each section in intervals of several days. By comparing
the images, they are able to identify the variable objects.
The team has assembled the individual images of the
268 sections into one comprehensive image. Following
a calculation period of several weeks, they created a 194
Gigabyte file, into which images taken with different filters
have been entered.
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Bochum University’s Chilean Observatory is one of those
located at La Silla in the Atacama Desert, one of the driest
and most inhospitable places on Earth. The photo at the
top of the page (and the extract of a miniscule portion of
it at left) were the result of five years of photography of
the Milky Way galaxy, with the 286 individual images
“stitched” together to form the 194GB file.
Online tool facilitates search
for individual celestial objects
In order to view it online, researchers headed by Prof Dr
Rolf Chini from the Chair of Astrophysics have provided
an online tool (http://gds.astro.rub.de/). Using this, any interested person can view the complete ribbon of the Milky
Way at a glance, or zoom in and inspect specific areas.
An input window, which provides the position of the
displayed image section, can be used to search for specific
objects.
If the user types in “Eta Carinae”, for example, the tool
moves to the respective star; the search term “M8” leads
SC
to the lagoon nebula.
December 2015 25
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