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HIPPARCHOS the Hellenic Astronomical Society Newsletter Volume 3, Issue 4

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HIPPARCHOS the Hellenic Astronomical Society Newsletter Volume 3, Issue 4 HIPPARCHOS The Hellenic Astronomical Society Newsletter Volume 3, Issue 4 ISSN: 1790-9252 Contents HIPPARCHOSHIPPARCHOS Volume 3, Issue 4 • July 2021 ISSN: 1790-9252 Hipparchos is the official newsletter of the Hellenic Astronomical Society. Message from the President .............................................3 It publishes review papers, news and comments on topics of interest to as- tronomers, including matters concern- REVIEWS ing members of the Hellenic Astro- nomical Society. Sensing the pulsations of empty space by Theocharis A. Apostolatos ...................................................4 Editorial board • Kostas Gourgouliatos A revolution in transient astrophysics (Physics Dept., University of Patras) by Giorgos Leloudas ...........................................................8 • Spiros Patsourakos Predicting Solar Energetic Particle (SEP) events: (Physics Dept., University current status and future perspectives of Ioannina) by A. Anastasiadis and A. Papaioannou . 14 • Kostas Tassis (Physics Dept., University of Crete) Characterising exoplanetary atmospheres: • Nektarios Vlahakis the legacy of HST/WFC3 (Physics Dept., University by Angelos Tsiaras ............................................................21 of Athens) Contact person Nektarios Vlahakis Physics Department, National and The 15th Hellenic Astronomical Conference Kapodistrian University of Athens, University Campus, The Hellenic Astronomical Conference, organized by the Hellenic Astronomical 157 84 Zografou, Society (Hel.A.S.), is the major scientific event of the greek astronomical com- Athens, Greece munity. The Conference, which takes place every two years in a different part of Tel: +30-210-7276903 Greece, typically brings together over 100 scientists with research interests in As- E-mail: [email protected] trophysics, Planetary Science and Space Physics. The 15th Conference of Hel.A.S. was originally planned to take place in Patras, Editorial Advisors from 5 to 8 July, 2021. However, the persistence of the COVID pandemic forced • Vassilis Charmandaris us to host the conference virtualy. (Physics Dept., University of Crete) We would have much preferred to seeing you in Patras, but we hope to least see you online instead! • Antonis Georgakakis Sponcored by: (National Observatory of Athens) • Costis Gontikakis (RCAAM, Academy of Athens) Printed by ZITI Publications • www.ziti.gr Cover Image: The Galactic Center: A detailed panorama explores regions just above and below the galactic plane. Different bands of X-rays from the Chandra Observatory (orange - hot, green - hotter, purple - hottest) have been combined with radio data (gray) from the MeerKAT telesccope. These data reveal threads of superheated gas and magnetic fields near the center of the Milky Way. Image Credit: X-ray: NASA/CXC/UMass/Q.D. Wang; Radio: NRF/SARAO/MeerKAT. Message from the President ver this past year, we have all been in person in Patras during the 15th major astronomy events that take place Oexperiencing the abrupt changes Conference of our Society, as it was in Greece, as well as an Instagram and in our daily lives imposed by the pan- originally planned. Our conference, Twitter account. Moreover, Hel.A.S. demic and several of us have had fam- like many others, will be held “virtu- supported the public outreach activi- ily and friends who have become sick. ally” during the second week of July ties of a dynamic group of Junior Mem- Moreover, the way we work, teach, and 2021. This appears to have facilitated bers, who established the “2 minute do science has been modified and in participation since over 200 astrono- Science” page, both on the web and on the process we became experts in using mers from 24 countries, both mem- Facebook, in order to share with the ZOOM, Webex and eClass along with a bers and non-members of Hel.A.S., general public in Greece their excite- variety of other teleconference tools. have registered to attend it, mak- ment about astrophysics and space ing it the largest ever conference or- physics. I do hope that they keep their Despite these challenges, our training ganized by our Society. The Scientif- enthusiasm and with the help of the in the new “tools of the trade” also en- ic Organizing Committee has select- next generation of astronomy students abled new opportunities. We have at- ed four exceptional scientists as ple- and postdocs will continue to provide, tended lectures and seminars from in- nary speakers, Dr. Francisco Colom- in Greek, interesting and high quality stitutes across the globe and participat- er (JIVE, The Netherlands), Dr. Athe- information about astronomy to our ed in conferences remotely. Sharing in- na Coustenis (Obs. de Paris, France), fellow citizens. formation in a reliable and user-friend- Prof. Avishay Gal-Yam (Weizmann In- ly manner has become much easier for stitute, Israel) and Prof. Kostas Kok- The Vice Chair of the Society, Prof. all. Our Society, following the popu- kotas (Univ. of Tuebingen, Germany), Nektarios Vlahakis, was also responsi- lar trend, commenced a monthly vir- and worked hard to prepare a dense ble in selecting and editing the four in- vited articles on pertinent areas of as- tual colloquium. A committee of three and diverse scientific program. In ad- trophysics, which appear in the pres- members of the Governing Council dition, the Governing Council decided ent issue of Hipparchos. Prof. Theo- – Nektarios Vlahakis, Spiros Patsou- to name one of the plenary lectures as haris Apostolatos is presenting the lat- rakos and Kostas Tassis – selected a “John H. Seiradakis Plenary Lecture”, est results in the quest for gravitation group of distinguished colleagues who in memory of Prof. John Seiradakis waves, Dr. George Leloudas is shar- presented 9 very interesting colloquia who passed away last year. As we all ing with us some of the wonders of the this past academic year. These were know Prof. Seiradakis played a critical transient sky, Dr. Anastasios Anasta- typically attended by over 70 of our role in founding the Hellenic Astro- siadis with Dr. Athanasios Papaioannou members and are now available as re- nomical Society and also was the Sec- provide the latest information on trac- corded videos in the YouTube channel retary of the Society from 1994 un- ing energetic particles emanating from of our Society. I would like to personal- til 1998 and President from 1998 un- the Sun, and Dr. Angelos Tsiaras is de- ly thank everyone involved, and in par- til 2002. scribing the ongoing efforts in charac- ticular the speakers who invested their terizing the atmospheres of exoplanets, time to share with us their results, and Over the past year, the Society, thanks on the eve of the upcoming launch of I do look forward for these colloquia to the investment of time and energy the James Webb Space Telescope from to continue for many year into the fu- of several members, also obtained a NASA and the Ariel mission from ESA. ture. more prominent presence in the so- I am certain that we will all enjoy and cial media. We now maintain an active learn a lot reading them. However, due to the restrictions of the Facebook page, where we share sci- pandemic, it was not possible to meet ence news and information about all Vassilis Charmandaris President of Hel.A.S. HIPPARCHOS | Volume 3, Issue 4 3 Sensing the pulsations of empty space by Theocharis A. Apostolatos Department of Physics, National and Kapodistrian University of Athens, Greece 1. Introduction orem, substantial developments in dif- The lack of physical experiments, ferential geometry, the tensor calculus where one could measure the differ- Struggling for almost a decade, after by Levi -Civita etc. ences between the new theory and the the annus mirabilis when he formulat- The idea of waves permitted by this celebrated for three centuries newto- ed Special Relativity, Albert Einstein new field (the field of the metric of the nian theory of gravity, as long as the ad- moved on to formulate General The- space -time itself) concerned Einstein vent of quantum mechanics lead Gen- ory of Relativity, which was completed himself, from the very beginning. In anal- eral Relativity to remain confined in a in 1915. Although the idea of a curved ogy to Maxwell equations which per- few small groups of mainly mathemati- space- time sounds rather simple, and mitted the existence of electromagnet- cians, scattered around the globe. Grav- well known, today, it was a radical idea ic waves, Einstein felt that his new set of itational waves were not an exception. at the dawn of the 20th century and full equations should allow for similar type In the famous book “Classical Theory of surprises. Famous physicists, like Lev of waves. However, the fact that the co- of Fields” of Landau and Lifshitz [1] that Landau, considered the idea of Einstein ordinates one could use to map space- was first published during the World as a unique idea in the history of Phys- time, apart of being continuous and dif- War II, and was translated in English in ics and have jealously described Gener- ferentiable, were completely free, led the 50’s, it is noted that the amount of al Relativity as “probably the most beau- him to a very difficult situation. One energy radiated by gravitational waves tiful of all existing physical theories”. Al- should somehow discern the true waves in he case of a binary system would be though the basic idea was conceived by if that had any meaning from the ficti- of the order of 10–12 of the total energy Einstein rather early, it took him years tious waves showing up just as an arti- of the system itself, and thus the time to overcome the mathematical obsta- fact of choosing crazy coordinates. Ein- scale expected to see its effects on the cles before he presented it in its right, stein faced that problem and was soon motion of the binary would be of cos- final form. Actually, it was David Hil- led to wave solutions moving at any pos- mic order.
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