View source for Mosaics

=What is a mosaic?=

A mosaic is a larger picture composed of many smaller pictures.  This way, you can get an image of a region much larger than the field of view of a single frame.

Here is an example taken from real life.  We'd like to take a picture of some friendly people standing in front of the 200-inch Hale Telescope at Palomar Observatory.  But our camera has a relatively small field of view, and we can either take a picture of the people, or the telescope, but not both at the same time.  So we take two pictures:

[[Image:pal200top.jpg]]

[[Image:pal200bottom.jpg]]


Then, after downloading the images from our digital camera, we use the computer to combine them together into one larger picture, covering the entire region we're interested in.

[[Image:pal200mos.jpg]]

Note here too that the mosaicking process compensated for distortion in the camera -- the edges of the image are no longer a straight line.

Real astronomical mosaickers do this too -- they combine smaller images into a larger image, and compensate for distortion in the camera.  The distortion is just (usually) much smaller than what is seen here.

=Spitzer mosaics=

Most of Spitzer's cameras have a field of view that is 5 arcminutes on a side.  But, by design, Spitzer is really, really good at covering huge areas.  So by taking many, many individual frames, we can combine them all together into huge maps -- Luisa has worked on maps that are more than 10 square degrees, containing about 21,000 individual frames!

In Spitzer jargon, an individual frame that has just been taken is called a '''Data Collection Event (DCE)''', or "raw data."  After it is processed through the SSC's pipeline, it is called '''Basic Calibrated Data (BCD)'''.  Many BCDs are combined into a mosaic, which is just one of several kinds of '''post-BCD products'''.

=[[Making mosaics using MONTAGE]]=

MONTAGE is a standalone package that allows you to make mosaics.