The area of the entire picture is measured in square degrees, so we take the number of degrees found in question 1 and square it to get: Now there are 4.13 x 104square degrees in the sky. From this you can figure out how many pictures you would need to take to cover the whole sky: Finally if it takes 10 days for each picture, we can figure out how long it would take to cover the whole sky with similar pictures: With a unit conversion of 365 days/year, we can determine the number of years it would take: Clearly, this is a very long time! This is an interesting point to note: astronomers can only take deep pictures of a small fraction ofthe sky. 50 it is not practical to count galaxies by taking pictures of the entire sky. 50 how can we proceed to figure out how many total galaxies there are. We can make an estimate by guessing that the number of galaxies in any particular picture will be the same regardless of where we point. We can then estimate the total number of galaxies in the sky by counting the number of galaxies in this one picture, and multiplying it by the number of pictures that it would take to cover the whole sky. Take a look at the image of the Hubble Deep Field (Figure 1). Almost every one of the objects you see in this picture is a distant galaxy. Count up all the galaxies in each section then add them up to get an estimate ofthe number of galaxies in this one field. Again, you can proceed quicker by taking advantage of the multiple members ofyour group; however, you might wish to have everyone in the group count one region independently to get some idea of the measurement uncertainty. Region A1: _ Region B1: Region C1: Region A2 Region 32: Region C2: Region A3: Region B3: Region C3: There are a total of galaxies in Hubble Deep Field