Understanding how the Universe evolved from a dense ball of superheated plasma to the vast canvas of stars and galaxies it is today—and what it will become next—remains a fundamental question asked throughout history. Today, we can begin to answer this question by making more precise measurements of objects in space, from our nearest neighbors to the deepest recesses of the visible Universe, than we've ever been able to before. The resulting maps help us frame the question of how the Universe unfolds by measuring how cosmic structure—the web of galaxies that make up the Universe—grows over time, according to the rules of physics. A key part of measuring this cosmic structure is to determine the distances to the many galaxies we observe with our telescopes.

Two powerful probes of dark matter on small scales—strong gravitational lensing and ultra-faint dwarf galaxies—join together to set world-leading constraints on the nature of the dark matter particle in a recent study led by KIPAC researchers, including the authors. In the process, we have shown that combining these probes provides a framework to detect “dark halos,” clumps of dark matter that have no associated visible light, using the vast amounts of deeper data promised by upcoming surveys. 

In Part I of this 2-part series on what astronomers do while observing, we looked at what happens when we take wide-field data for the cosmological side of things, and here in Part 2 we will continue with discussing the other mode that most people think of when they imagine what astronomers do at a telescope: searching for specific interesting objects.

I recently returned from an observing run at a telescope in Chile, and I thought our readers might wonder what astronomers do when they’re observing. After all, it can’t all be sitting around romantically staring up at the stars, right? So here’s a detailed description of what I did when I was observing for those who have wondered what actual observing is like.