Chopping (astronomy)
Chopping is a technique used with infrared telescopes to minimize interference from external or internal heat.[1] The chopper is the mechanism that rocks a mirror (typically a secondary mirror) inside a telescope back and forth in rapid succession because background radiation would change too quickly to measure otherwise.[2]
Drawbacks
[edit]There are two major drawbacks to using the method of chopping. First is the variance of the background radiation. This can change when the telescope is shifting between the beams making thing appear strange. Secondly, this method can only be used when the object in question is not too far away, because otherwise it would be out of the telescope's range.[3]
Infrared Telescopes
[edit]Main: Infrared telescope
With Infrared Telescopes, chopping is used to eliminate the background radiation by taking pictures at slightly different angles. By comparing separate images, it becomes much easier to tell what the background heat is and what is coming from the object in question. This allows it to be used to gain information about the object that a visible light telescope or a UV telescope can't see.[4]
Gemini Observatory
[edit]Main: Gemini Observatory
The Gemini Observatory is a set of two telescopes with one in Hawaii and the other in Chile. Both of these telescopes are infrared and both use chopping to eliminate background radiation. The telescopes chop their secondary mirrors at a rate of 3-5 Hz. Both observatories utilize tilt-tip correction to ensure that the image quality remains crisp. The observatories also received help from the University of Florida to improve its chopping mechanism.[5]
SOFIA Telescope
[edit]Main: SOFIA Telescope
The SOFIA Telescope was an infrared telescope integrated into a Boeing 747. This telescope utilized its Second Mirror Assembly (SMA) primarily for chopping and also partially for small corrections. The signals that the SOFIA Telescope would be searching for could be tens of thousands of times less significant than the background emission, so the telescope has an average chopping frequency of 2-5 Hz, but can reach rates of 20 Hz. The chopping action follows a square wave pattern.[6]
James Webb Space Telescope
[edit]Main: James Webb Space Telescope
Although the James Webb Space Telescope is an Infrared Telescope, it doesn't use chopping action to prevent interference. Instead, it uses gold-coated mirrors to reflect almost all heat.[7] Additionally, it doesn't use chopping because it is meant to bore into deep space, and the angle would have to be refocused depending on how far away the object is.
See Also
[edit]References
[edit]- ^ Mason, Rachel (22 August 2006). "Chopping and Nodding". www.gemini.edu.
- ^ Goodrich, Bob (12 November 1998). "How does a Chopper Work". www2.keck.hawaii.edu.
- ^ Bertero, M; Boccacci, P; Benedetto, F Di; Robberto, M (1 April 1999). "Restoration of chopped and nodded images in infrared astronomy". Inverse Problems. 15 (2): 345–372. Bibcode:1999InvPr..15..345B. doi:10.1088/0266-5611/15/2/002. Retrieved 18 July 2024.
- ^ "Background radiation in the mid-IR". www.naoj.org. 28 August 2001.
- ^ Roach, P. F. (2004). "Mid-infrared instruments on the Gemini 8-m telescopes". Advances in Space Research. 34 (3): 583–588. Bibcode:2004AdSpR..34..583R. doi:10.1016/j.asr.2003.05.028. Retrieved 18 July 2024.
- ^ Reinacher, Andreas; Graf, Friederike; Greiner, Benjamin; Jakob, Holger; Lammen, Yannick; Peter, Sarah; Wiedemann, Manuel; Zeile, Oliver; Kaercher, Hans J. (December 2018). "The SOFIA Telescope in Full Operation". Journal of Astronomical Instrumentation. 07 (4). Bibcode:2018JAI.....740007R. doi:10.1142/S225117171840007X. ISSN 2251-1717. Retrieved 18 July 2024.
- ^ Cohn, Haleh (12 July 2022). "James Webb Space Telescope". www.mcgill.ca.