SOUTHERN MAINE ASTRONOMERS Monthly meeting Thursday, September 7, 2017 7:00 p.m. at the Southworth Planetarium Speaker: Nishu Karna Free and open to the public From Ron Thompson, SMA President: We have a guest Speaker this month, Nishu Karna, Ph.D. and she will be discussing "Coronal Cavities on the Sun". ABSTRACT: Coronal cavities are large-scale structures in the Sun's corona that are closely related with the long-term evolution of the magnetic field in the photosphere as well as associated with the energetic solar activity such as prominence eruptions and coronal mass ejections (CMEs). Coronal cavities are observed as elliptical-shaped, relatively low density, dark regions above the solar limb in extreme ultraviolet (EUV), Xray, and white-light coronal images. The locations of cavities at high latitudes can be used to establish the time of polar magnetic field reversal. Cavities are vital clues to the state of the solar corona just prior to some CMEs and changes in the cavity may trigger CMEs. The study of the properties of cavities from formation to disruption will help us understand a CME&r squo;s structure before it erupts and will also lead to improving predictions of space weather effects. BIO: Nishu Karna is a postdoctoral research fellow at Harvard-Smithsonian Center for Astrophysics. Her research work focuses on understanding the correlation between cavities, prominences, and magnetic field topologies, by combining high-resolution space-based observations with advanced Non Linear Force Free Field modeling. She received her Ph.D. degree in Computational Sciences and Informatics (Solar Physics) in May 2016 from George Mason University. During her Ph.D. she worked on two solar topics: the first one was to measure the areas of a polar coronal holes using Extreme Ultra Violet and magnetic field synoptic maps for spanning two solar cycles (Solar Cycle 23 and 24). The second topic was her dissertation work on coronal cavities. She made a comprehensive study of coronal cavities from May 2010 to Feb 2015. The comprehensive study includes the development of cavities detection tool, measurements of each cavity's structure (length, width, height), the correlation between each cavity`s height, width and length, cavities evolution with the solar cycle, and polar crown cavities formation mechanism. Hope to see you there. Doors open at 6:30. Ron Ron Thompson Southern Maine Astronomers