of the maximum temperatures around their
average. What is the probability of seeing a value this large by
chance? In other words, did the Sun vary significantly during the four
hours of observations?
Purpose: In this part of the lab you will use your data to investigate the brightness of the Sun and the performance of the radio telescope.
Analysis:
During a few noise calibrations the noise diode failed to turn on. This
results in large values for calcons, the receiver temperature,
and the antenna temperature. Ignore such blocks in your analysis.
A. The offsets for the maximum solar temperature
The offsets from the Sun yielding the maximum antenna temperature for
each raster scan during the entire week's worth of observations are in
\\Hubble\ph343\lab3\alloffs.txt.
This file will also be available on the class web site.
The columns in the file are the day number, the hour of the observation,
the azimuth at the end of the scan, the elevation at the end, the
azimuth offset, and the elevation offset.
1. Plot both the azimuth offset and the elevation offset vs
the azimuth. Describe how the offsets change with azimuth.
2. Discuss whether the plots show any evidence that the rotation axes of the antenna are not exactly horizontal and/or vertical.
B. The path of the Sun through the sky
1. Use the data in alloffs.txt to plot the elevation of the Sun vs the
azimuth.
2. At what azimuth does the maximum elevation of the Sun occur? Explain why the maximum occurs at this azimuth.
3. Did the maximum elevation of the Sun change during the course of the week? If so, how? Can you explain the reason for any change?
C. The receiver calibration
The calibration data from the entire week's worth of observations are in
\\Hubble\ph343\lab3\allcals.txt.
This file will also be available on the class web site.
The columns in the file are the day number, the hour of the observation,
the azimuth at the location of the calibration, the elevation of the
calibration, the calcons, and the receiver temperature.
1. Is there any large variation of the calibration from day to day?
Do any variations correlate with the weather (see the table on the next page)?
2. Plot antenna temperature vs elevation and similarly vs azimuth. Is there any evidence for a variation with elevation or azimuth? State your conclusions and support them with the evidence. A change could result from a changing spillover contribution or a changing signal from the Earth's atmosphere.
| day | weather |
| 276 | not recorded |
| 277 | Cloudy with drizzle |
| 278 | mostly sunny, mid to upper 70's, breezy enough to |
| move the antenna later in the afternoon | |
| 279 | sunny, 60's, slight breeze |
| 280 | mostly cloudy, but no rain |
| 281 | mostly sunny, 50's - 60's |
| 282 | mostly cloudy, but no rain, 50's - 60's, no wind |
| 283 | cloudy, drizzle to rain later, 60's, slight breeze |
D. Variability within 15 minute blocks of observations
1. Use the quicklook plots to investigate whether the measured
antenna temperature has errors due to pointing errors and, if so, how
large these errors are. In particular, are there any jumps in the
antenna temperature when the antenna moves (i.e., when the
azimuth or elevation changes)? Does the antenna temperature typically
change with any pattern within a block? State your conclusion and
show/discuss the evidence that you used to reach that conclusion.
2. Use the plots to choose your 15-minute block of data which appears to show the least variability. Read this block of data into Excel.
3. Repeat part A-2 from last week's lab for this block of data (use all of the data, not just 100 sets of 10 temperatures).
4. Similarly, repeat parts A-3 and A-4 from last week's lab for these data.
5. Compare the average of the temperature uncertainties with the rms scatter of the average temperatures around their average (as in part A-5 of last week's lab). Is there evidence for real variability of the signal during the block of data? Why? If there is real variability, what do you think that its source is? Give the reasons for your answer.
E. Variability between 15 minute blocks of observations
If pointing errors have been causing variations of the measured antenna
temperature, then the best estimate of the real signal from the Sun is
probably the maximum measured temperature during a 15 minute block.
1. Find the maximum measured temperature for each of your blocks of data.
Subtract the receiver temperature from the signal and scale the result to
the average of your calcons values (as discussed in class). List these
values with their uncertainties. You may want to exclude some blocks if
you believe that none of the temperatures are reliable. If you do so,
state which blocks you excluded and why.
2. Calculate the average of your maximum temperatures and the scatter around their average.
3. Calculate and report the of the maximum temperatures around their
average. What is the probability of seeing a value this large by
chance? In other words, did the Sun vary significantly during the four
hours of observations?