Please do not zoom in or zoom out after that if you

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Unformatted text preview: ich the field has approximately 5 minutes of arc size (verify that the label in the lower right hand corner of the Sky window shows a number close to 0◦ 05￿ ). Please do not zoom in or zoom out after that. If you do or if you decided to choose your own random field (feel free to do so), please zoom again to the point when the label is as close to 0◦ 05￿ as possible. This is because we want to compare counts of galaxies within the same area of the sky in different places, which requires that the size of the patch we use is the same (5 arcminutes in our case). Also do not resize the Google Earth window as you count galaxies in different fields, your counts may be affected if you resize the window. Once the Sky finishes its zoom, wait until the SDSS Galaxy Query layer identifies galaxies brighter than apparent magnitude in r band of mr = 21 in the SDSS catalog. Once the layer queries the SDSS database over the internet, the galaxies in the field will be marked by circles. Count the number of marked galaxies in the field and then click on field 2 and repeat the exercise. For this part of the lab we need to discuss a little bit of statistics. As you know, statistics is a big part of analysis of data in various fields: physics, biology, economics, etc. The statistics of counts of relatively small random samples of objects is typically governed by what is called the Poisson distribution. For example, if galaxies were distributed completely uniformly on Google Sky is an extension of Google Earth software into the sky (the simple version of which, Google Maps, you probably have used to get directions, view a map, etc.). See the description of Google Sky that will be distributed to you, as well as video introduction to Google Sky at 4 PHSC12000 V1.0 4 the sky, we would expect that the probability to find a given number of galaxies in a field of a given size is given by the Poisson distribution. The key feature of this distribution is that ¯ if the average number of galaxies per field of...
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This document was uploaded on 02/13/2014.

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