Imaging
The SDSS uses a camera attached to their telescope to capture images of astronomical objects, this is photometric data. This camera has five filters that capture light at different frequencies, the bands are:
- U – Ultraviolet light
- G – blue and green in the visible band
- R – yellow and red in the visible band
- I – infrared light
- Z – near infrared
It is sensitive to light from ~300nm (near-ultraviolet) to ~1050nm (near-infrared).
Magnitude
This image shows some of the filters of the SDSS camera
The camera also measures the amount of light passing through each filter. This is the intensity of light in each band and relates to brightness of the object. The magnitude of an objects describes how bright it is. There are two types of magnitude:
Apparent magnitude – is a measure of how bright something appears to be from our perspective on earth. This is affected by many external parameters such as our distance from the object, which can make it appear fainter. It does not tell us how luminous the object is. Absolute magnitude – how bright the object would be at a standard distance away from us.
Magnitudes are measured with a reversed scale, the brighter the object the smaller the magnitude. For example, the sun had an apparent magnitude of -27, the moon has an apparent magnitude of -13. The sun appears brighter than the moon.
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All image credits to SDSS