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\subsubsection{In-class exercises}  Rather than lecturing about crucial concepts during the lab, we instead give short in-class exercises to refresh and deepen understanding of concepts introduced in the course lectures. These in-class exercises are meant to stimulate discussion within the lab groups, with the goal of either scaffolding concepts that will be needed for the next lab or reviewing particularly difficult concepts from the previous lab (Fig.\ \ref{fig:inclass_lab} contains lab.  An example set of exercises has the students consider  an example). Instructors image of a nova (Fig.\ \ref{fig:inclass_lab}) and answer the following questions about its signal-to-noise.  \begin{quote}  Consider the attached image of a nova observed with the millimeter telescope CARMA at 96 GHz (Panel A). Histograms of pixel values are shown in Panels B and C (Panel C is just a zoom-in of a region on Panel B); these are just like the histograms you made in DS9's \texttt{Scale Parameters}. The pixel values after calibration are expressed as flux density per pixel (units of mJy/pixel). The plotted range ($-2$ to $36\,\mathrm{mJy/pixel}$) includes all pixels in the image.  \begin{enumerate}  \item Estimate the average background value ($\bar{S}$) and explain your reasoning.  \item Estimate the standard deviation of the background ($\sigma$), and explain your reasoning.  \item Estimate the peak flux density of the nova ($S_{\mathrm{max}}$), and explain your reasoning.  \item Astronomers usually only take detections seriously if they are 5 or more $\sigma$ significant---that is, if the detected source is at least five times brighter than the   standard deviation of the background. In other words, the source's peak flux should be $S_{\mathrm{max}} > (\bar{S} + 5 \sigma)$. Estimate how many sigma the peak flux density of the nova is, and show your reasoning. Would this detection be taken seriously by other astronomers?  \end{enumerate}  \end{quote}  While the students work on the exercises, the instructors  circulate around the room and answer questions as they arise. After 20--30 minutes, students write their conclusions and submit their in-class the  exercises. In-class exercises only compose a tiny portion of the grade and are only assessed for effort; this assessment ensures, however, that students engage with the material.