|
This is my baby; giant spiral galaxy IC 342. It lies just beyond
our own Local Group of Galaxies in another group called Maffei
Group or IC342/Maffei Group. The image above is a combination
of images taken with BVRI filters (roughly blue, visual = green, red, and
infrared) by Yours Truly and Dr. Kari Nilsson at the Nordic
Optical Telescope (NOT) on 18 January 2002. The image shows only a
small section in the north-western quadrant of the entire galaxy. The
reason is that the field of view of Alfosc instrument at the NOT
is about 6 arc minutes (one tenth of a degree) and hence much less than
the size of the galaxy. The image below shows the entire galaxy (most of
it anyway) in a field of view of 20.5 arc minutes and which part of the
galaxy is shown in the image we took. The greyscale galaxy image was
obtained from Skyview using Digitized Sky Survey database.
|
|
|
Here is another giant spiral galaxy M101 or Messier 101. This
is farther away than IC 342, at about 8 Mpc from us. It is the centre of its
own M101 group of galaxies. The image is a combination of images
totalling 1320 sec in B filter, 960 sec in V filter and 780 sec in R
filter taken by Yours Truly at the Nordic Optical Telescope (NOT)
on 22 March 2000. The instrument was Alfosc with a 6 arc minute
field of view. The image shows the central part of the galaxy out to
perhaps 80% of the radius of what is visible in optical wavelengths.
What makes this image spectacular is the absolutely fabulous seeing of
0.5 - 0.8 arc seconds at the time of exposures.
|
|
This is not a typical pretty image you get when you go through all the
trouble of combining images taken with various colour filters (like the
two images above). This is an almost raw image from a telescope. It has
been bias-subtracted and flat-fielded (to correct for instrument and
filter errors) but otherwise it is unprocessed (there are still traces
of cosmic rays visible in the image). The reason this image is presented
here should be clear from its appearance. It is the strangest image ever.
If a telescope moves during an exposure, stars are elongated into stripes.
If a satellite or airplane moves across the field of view, you get stripes.
But no combination of a multitude of these phenomena should be able to
cause so many stripes of different alignment and brightness and some of
them even stopping in the middle of the picture. (And my dear layman
readers: it is not a case of intergalactic war, UFOs, or any such crazy
idea either.) The image was taken by Yours Truly at the Nordic Optical
Telescope (NOT) on 25 February 2003. The instrument was Alfosc
and the exposure is of 300 sec in B filter. The galaxy in the centre is
UGC 8882.
|
