IntroductionIn this report we summarize the progress of the course transformation project for the USC Columbia course  ASTR101: Introductory Astronomy.  During the spring 2017 semester our team hassecured supplemental funding in the form of a $4k grant from the SC Space Grant Consortium, through the Research and Education Awards Program (REAP)conducted surveys to better understand the ASTR101 studentsdiscussed and re-evaluated learning goals for the courseconsulted with USC College of Education Professor Suha Tamim on the implementation of team-based learning in large classesmet with graduate student teaching assistants and lab instructors to evaluate the management of laboratory instruction and assessmentcollected material from colleagues at other universities for alternate lab activitiesdeveloped and beta tested a new solar telescope lab activityengaged students in testing out a new instructional video game, developed by textbook publisher Norton for introductory astronomy courses The remainder of this document is organized as follows: In section \ref{140131} we outline the scope and overall goals of this transformation project.  Section \ref{295101} describes our understanding of the students taking ASTR101.  Section \ref{566769} addresses the course learning outcomes, and in Section \ref{485152} we discuss classroom techniques and assessment strategies.  References are in Section \ref{626481}  and the Appendix (\ref{174502}) includes figures and text summarizing the data we have collected from student surveys.Project ScopeBoth primary instructors (Rodney and Tedeschi) are interested in applying evidence-based pedagogy, and have been using elements of active learning in the large lecture classes — but we would like to do more of this, and do it better.  We see opportunities to creatively re-structure the course scheduling and make use of alternative classroom spaces to allow more small-class experiences for our 200+ students.  We are particularly interested in exploring team-based learning as a way to give students more collaborative experiences in both the lecture and the lab components of the class.   The ASTR 101 course offers an excellent “sandbox” to test out a course transformation process that might eventually be extended to the rest of our department.  In 2-5 years, we may be in a position to take the active and collaborative learning practices incubated in ASTR 101 and translate them out to the larger pool of introductory physics classes.The ASTR101 StudentsTo inform our definition of learning goals, we first want to ask "Who are the students taking ASTR101, and why are they taking this class?"What the Instructors' Expected Before examining any data, we drew on our anecdotal experience to describe the types of students that take ASTR101: Diversity of Goals:   We believe that only a very small minority of students in ASTR101 are taking this course because they perceive the subject matter to be critical to their careers. Our students will tend to have a much wider range of primary motivations for taking ASTR101, compared to, e.g., the large "pre-med" freshmen cohort in BIOL101.Wide Range of Math/Science Experience:   Astronomy is a very approachable scientific discipline that can feel more accessible to non-science majors who might be daunted by other courses that could satisfy the Carolina Core SCI requirement.  We expect that many of our students choose astronomy in part because they have some degree of math anxiety.  For many of our students ASTR101 will be their first exposure to a science course at USC.  We anticipate that this same attribute of accessibility also attracts a significant number of students in their 3rd year or beyond.  These juniors and seniors may be neck-deep in upper-level courses that advance their major, and they add the ASTR101 course as a break from their discipline,  while conveniently satisfying an elective requirement.The ASTR101 course is also the first step towards earning an Astronomy Minor at USC, and is therefore also reaching a small population of students who are deeply excited by the study of the universe, and may come in the door with a great deal of prior exposure to our subject matter and in some cases a very sophisticated skillset in mathematics, computing and physics.What the Students SayTo better understand our class make-up, we conducted a survey of ASTR101 students, asking a series of questions about their motivations, goals, and background.  We received a 76% response rate.  The results from this survey are briefly summarized here, and figures detailing specific responses are in the Appendix (\ref{174502}).   The survey in general bore out the expectations of the instructors described above:Our students are young, with diverse career interests: More than 3/4 of the students have graduated from high school within the last 2 years (Figure \ref{610325}).  Nearly 1/3 are in their first year of college (Fig. \ref{968458}).  Asked about their career aspirations, the most popular choices are in the Arts/Humanities or the Sciences (Fig. \ref{844080}). Engineering, computing and medicine are the least popular among ASTR101 students.  Most students report interest in several categories, indicating that they are still "undecided" about their eventual career plans -- perhaps unsurprising given their typical age and experience.They need this class: More than 3/4 report that they are taking the class at least in part because it satisfies a graduation requirement (presumably the Carolina Core SCI component).  We infer from this that most are taking this class in lieu of another intro science course that could satisfy the Carolina Core.They find science interesting, but primarily as "casual consumers":  Nearly half of the class indicated that they are "very interested in astronomy."   Roughly 12% selected interest in astronomy as the only reason for taking the course (compared to 35% that selected credit for graduation as the only reason).   More than half of the class expressed high levels of interest for engaging with science through friends, family and the media.  However, less than 1/4 of the class was interested in what we would characterize as deep engagement in science: joining a science club, teaching science at K-12 or college levels, pursuing science in grad school, or as a career. Most are comfortable with science, but many are not confident in their math skills: In questions about confidence in evaluating and discussing science, we consistently had ~70% report high or very high confidence.  The one exception that shifted the skew was when mathematics was explicitly included.   Students were asked to rate their ability to "Understand mathematical and statistical formulas commonly found in scientific texts,"  and this had 57% of students on the low confidence side.  Notably, a more specific question with a mathematics focus brought out higher confidence.  Asked about their ability to "Handle the mathematics required for this course (algebra, not calculus; estimation and approximation without using a calculator)" we again had >70% report high confidence.   This suggests that the ASTR101 course may be particularly valuable for building up the confidence and skills of students who enter with some generalized math anxiety.The course logistics are not a problem: We also surveyed the students about their preferences for certain structural aspects of the course that are under our control (to some extent).  We found that the students taking ASTR101 place high importance on the timing of the class (the day of the week and/or time of day; see Figure \ref{105142}).  They are not especially sensitive to the cost of the textbook, and have a slight preference for a physical textbook over an online e-text.  A non-negligible minority of students (34%) would prefer an online course (Figure \ref{238335}), which is notable because there is an inherent selection bias in that this survey was only given to students who were able to enroll in the in-person lecture class.  Although we do not intend to implement an online version of ASTR101 at this time, this prompts us to consider future development of an online version as we proceed through this course transformation process. At the end of the Spring 2017 semester, anonymous comments from the ASTR101 students in the USC course evaluations reinforced the above assessments.  A sampling of these comments are included in the Appendix (\ref{602696}).

INTRODUCTION The Spock transient events—separately designated and —appeared in Hubble Space Telescope () imaging collected in January and August of 2014, respectively (Figure [fig:SpockDetectionImages]). These observations were centered on the galaxy cluster 0416 (hereafter, 0416) and were collected as part of the Hubble Frontier Fields (HFF) survey (HST-PID:13496, PI:Lotz), a multi-cycle program for deep imaging of 6 massive galaxy clusters and associated “blank sky” fields observed in parallel (Methods [sec:Discovery]). Combining the imaging and lens models of the 0416 gravitational lens leads to three key observables for the events: (1) they are both more luminous than a classical nova, but less luminous than almost all supernovae (SNe), reaching a peak luminosity of roughly 10⁴¹ erg s−1 (MV = −14); (2) both transients exhibited fast light curves, with rise and decline timescales of ∼2–5 days in the rest frame; and (3) it is possible that both events arose from the same physical location but highly unlikely that they were coincident in time—they were probably separated by 3-5 months in the rest frame. These transients thus present a puzzle: they are broadly consistent with the expected behavior of stellar explosions (they each exhibit a single isolated rise and decline in brightness), but they can not be trivially classified into any common category of explosive astrophysical transients. The HFF survey was not designed with the discovery of peculiar extragalactic transients as a core objective, but it has unintentionally opened an effective window of discovery for such events. Very faint sources at relatively high redshift (z ≳ 1) in these fields are made detectable by the substantial gravitational lensing magnification from the foreground galaxy clusters. Very rapidly evolving sources are also more likely to be found, due to the necessity of a rapid cadence for repeat imaging in the HFF program. These unusual characteristics for an survey enabled a precise measurement of the lensing magnification for SN Tomas, a high-redshift thermonuclear (Type Ia) SN . The HFF imaging program also contributed to the detection and characterization of SN Refsdal, a high-redshift core-collapse SN and the first strongly-lensed SN observed with multiple resolved images . The long-term monitoring campaign of SN Refsdal then led to the discovery of the peculiar lensed transient _Icarus_, which is posited to be a stellar caustic crossing event . Even among this collection of rare transients, the events appear to be unique. No single astrophysical model is clearly sufficient to explain all of the available observational data, and the best available models require either an extreme stellar source or a very unusual gravitational lensing configuration.