The reasons for making polarization observations of the Moon
- We can obtain another measure of the instrumental polarization by measuring the polarization of the
center of the Moon. We have already
determined the instrumental polarization via polarimetry of SgrB2 done in late April, but it is useful to
have a another check of this. Near its center, the Moon is known to be unpolarized.
- The edges of the Moon exhibit a radial polarization pattern. Thus, if we can see this radial pattern we will
have confirmed that we are correctly calculating the angle of polarization.
- Greg's scripts are all you need for observing the Moon. Don't use any of your
perl scripts, or other software that you have developed. Greg's scripts are in
~viper/sparo2003/moon. All the scripts below share moongeneric.tcl . Therefore,
in order to center up any and all of these scripts, you should only change the
::pmodel::xoffset and ::pmodel::yoffset in this one place.
New as of 07/14/03:
- moonbigphot is for verifying the pointing. It makes a 5 x 5 map. It should take a half-hour
to run. You will need to run sparomap on the resulting data.
- mooncrossphot is a quicker method for verifying the pointing. It takes only five minutes but makes a sparse
map of just
five pointings. Once again, you will need to run sparomap on the resulting data.
- mooncenterpol does polarimetry towards the center of the Moon. It takes three polarimetry files, so it should
take about a half-hour to run. If you repeat this twice, we should have all the data we need for this test.
- moonlimbpol does polarimetry at the center and at three limbs (= edges) of the Moon. It should take 40 minutes
to run. Run this once and we will be done with this test.
- fakecenterpol allows you to test Greg's ability to track the Moon while you are still in the upper actuator
position. It is the same as mooncenterpol but it deliberately points too high, so as to place you in the upper
- moonrowphot scans from west to east across the middle of the moon,
mapping a 5x1 region.
- mooncolphot does the same thing, except it goes from south to north down the
middle of the moon, mapping a 1x5 scan region.
- mooncenterpol1 ... mooncenterpol9 are versions of mooncenterpol that center the nth pixel
on the moon. This assumes 24-degree array tilt and 3.3' array spacing.
Some things to keep in mind when observing the Moon:
- It has been a few months since you changed actuator positions. So you might want
to re-read the instructions that I posted for you on the web page. look under
Plans --> Instrumental Polarization --> section on Sgr B2 observations; there you will
find the link to these instructions.
- It is possible to saturate the data system when looking at the Moon. To check
for saturation, point at the center of the Moon and set the strip chart attenuation
on the Mac to 1024. If the
is bigger than 3 cm on the Mac screen, then you are too close to saturation, and you must
the preamp gain by a factor of 10. This is done via a switch on a box in rack 4 of the control room.
This box is the same box that supplies
the voltage for the Helium-3 charcoal pump heater in SPARO. Look at the box, and it
should be clearly labelled so you can see how you can reduce the preamp gain by a factor of 10 (from 10,000 to
When the Moon gets to its highest elevation, it will be possible to detect it with SPARO even when it is not in the
Moon door. Specifically, on Saturday NZT, Sunday NZT and Monday NZT the Moon will be high enough to make it
possible for you to see it over the ground shield. So you won't need to lower the Moon door to get started
looking for the Moon with SPARO. However, the polarimetry observations should be taken through the Moon door with
the Moon door lowered. For these precision observations, we must avoid any vigentting of the signal by the ground
- The pointing accuracy needed is 0.05 degrees. The reason for this is that the Moon is big, and we don't need
to be precisely pointed for any of the Moon observations.
Contact email@example.com. Last updated July 11, 2003.