At the beginning of an engineering course, students learn to measure with different instruments, emphasizing dimensional analysis, clear understanding of different scales of physical magnitude, and analysis of aggregated errors. These measurements are intensely explored, because knowing how to manipulate them is essence to understand the physical concepts that will be covered in more detail in later topics. Usually at this stage, the student has contact with ordinary dimensions. In order to expand this exploration, we propose inclusion of a telescope as an angle gauge for astronomic measurements. A 12-inch reflecting telescope was used for this activity, carried out by 30 engineering students. Using their smartphones coupled to the telescope, they took images of the Moon. With the same camera/telescope setup, they took photos of an open star cluster to determine the angular size of the images, using stellar coordinates. They explored image resolution concepts imposed by the optical system and atmosphere, and the effect of illumination on the determination of the position of the crater rims. To convert the angular measurements into kilometers, they were encouraged to explore the most accurate information on the ephemeris of the Earth-Moon distance. The students compared their results with the tabulated values, and the errors in the measurement were presented along with a discussion. A pretest on basic concepts of “astronomical measurements” was applied before, and as a posttest, after the activity. The results were analyzed with the Cohen’s D effect size. Here we present the positive educational gain attained with this activity.