A week in the life of AMI

One of my jobs as the outreach officer at the Cavendish is to take people out on tours at of the Mullard Radio Astronomy Observatory (MRAO). This is something i very much enjoy but alas quite often none of the telescopes appear to move. This is due to them normally tracking a source for quite some time. They will slowly move with the sky but unless they move to another source, which they do for calibration purposes, you don’t see this happen. Quite often the time spent at one of our telescopes is too short to see this movement. So to illustrate this I’ve made a couple of time-lapse movies to show the Arcminute Microkelvin Imager (AMI) large and small arrays actually moving over the course of a week.

The Large Array consists of the eight 13-m dishes:

The Small Array consists of ten 3.7-m dishes:

I hope this nicely shows that they do indeed move about! If you can’t see the videos above please try: large array, small array.

Oh and for those of you who are interested, these videos were made with a cron job automatically grabbing the webcam feed with wget every hour and then using ffmpeg to do the conversion into a movie:

x=1; for i in *jpg; do counter=$(printf %04d $x); mv "$i" img"$counter".jpg; x=$(($x+1)); done
ffmpeg -r 6 -b 3200 -i img%04d.jpg output.mp4

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2 responses to “A week in the life of AMI”

  1. BigStew says :

    Forgive my ignorance…but when the telescopes suddenly all move to a different position (and not tracking) is that when they are calibrating? And why do they need to do that? Sorry if this is a basic question…

  2. samuel says :

    No that’s a good question.

    In my blog posting I almost suggested that the telescopes only move due to calibration. They will also move to go to other target astronomical sources. Quite often though they will stay tracking for quite some time. They will normally move to a calibration source on order of 10mins to an hour depending on the telescope and the observations they are doing. When they move to another source that will be the sudden motion. We calibrate radio telescopes against sources in the sky. Assuming they have known properties. Its the easiest way to do this. There are typically two types of calibration observations, primary flux calibration and secondary calibration observations. The primary observations typically are of a very bright source, e.g. 3C286, and are at the start and end of the observations. The secondary observations are normally of a source that is quite close to the target field (so the telescope doesn’t have to waste time moving) and are normally not as bright.

    I hope this answer the question.

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