Edward M Sion (born January 18, 1946) is an American astrophysicist who is Professor in the Department of Astrophysics and Planetary Science at Villanova University. He specializes on the structure and evolution of white dwarf stars and white dwarf stars in explosive binary star systems known as cataclysmic variables. [1]
Edward M. Sion is a US citizen of Lebanese descent. [2]
Sion received a BA in Astronomy from the University of Kansas in 1968 and an MA in Astronomy from KU in 1969. [3] He received a PhD in Astrophysics at the University of Pennsylvania in 1975. [4]
In 1977, Sion co-authored the Catalogue of Spectroscopically Identified White Dwarf Stars with George P. McCook. [5] The book was converted to an online directory by Villanova University and contains over 20,000 identified white dwarf stars. The catalog introduced the WD-number, which uses the equatorial coordinate system to identify each white dwarf on the sky. [6] The book and database are frequently referenced in journals since its creation.
Sion led a team of collaborators who developed the fundamental classification system of white dwarf stars in 1983. [7] This system is used worldwide, and characterizes both the chemical composition class and surface temperature of each known white dwarf star. [8]
In 1984, Sion uncovered empirical evidence that the hydrogen-rich white dwarfs transform into helium-rich white dwarfs when deepening helium convection, as a white dwarf cools, mixes hydrogen downward. [9]
In the mid-1990s, Sion led a team of collaborators, using the Hubble Space Telescope, to unveil the physical properties of white dwarfs in explosive cataclysmic variables and how they cool and heat in response to the accretion of mass from a sun-like companion star, a process which leads to nova explosions and, for the most massive white dwarfs, supernova explosions. [10]
From 1996, he served as associate editor of The Astrophysical Journal for six years.
The Lebanese government founded a non-profit in 2007, which would become their national academy of sciences. Sion was invited to be a founding member of the national academy, the Lebanese Academy of Sciences, a clone of the French Academy of Sciences. [2]
Sion's studies of white dwarf stars has led to his publishing over 588 scientific articles of which 246 peer reviewed articles have appeared in journals such the Astrophysical Journal, [11] Astronomical Journal, Astronomy and Astrophysics (the European Journal), [12] Publications of the Astronomical Society of the Pacific, [13] and the Monthly Notices of the Royal Astronomical Society. [14] Sion also acts as a featured expert on Big Think, [15] he has also provided commentary for Forbes. [16] [17]
With over 649 scientific publications, 64 of which share authorship with Villanova students, Dr. Sion continues to have a strong impact on the field and has been ranked in the top 2% of researchers globally by Stanford University since 2019. [18]
Sion has served sabbatical appointments at Arizona State University, Centre Nationale de la Recherche Scientifique, University of Toulouse and the Hubble Space Telescope Science Institute. [2]
A globular cluster is a spheroidal conglomeration of stars that is bound together by gravity, with a higher concentration of stars towards their centers. They can contain anywhere from tens of thousands to many millions of member stars, all orbiting in a stable, compact formation. Globular clusters are similar in form to dwarf spheroidal galaxies, and the distinction between the two is not always clear. Their name is derived from Latin globulus. Globular clusters are occasionally known simply as "globulars".
A star is a luminous spheroid of plasma held together by self-gravity. The nearest star to Earth is the Sun. Many other stars are visible to the naked eye at night; their immense distances from Earth make them appear as fixed points of light. The most prominent stars have been categorised into constellations and asterisms, and many of the brightest stars have proper names. Astronomers have assembled star catalogues that identify the known stars and provide standardized stellar designations. The observable universe contains an estimated 1022 to 1024 stars. Only about 4,000 of these stars are visible to the naked eye—all within the Milky Way galaxy.
Crater is a small constellation in the southern celestial hemisphere. Its name is the latinization of the Greek krater, a type of cup used to water down wine. One of the 48 constellations listed by the second-century astronomer Ptolemy, it depicts a cup that has been associated with the god Apollo and is perched on the back of Hydra the water snake.
40 Eridani is a triple star system in the constellation of Eridanus, abbreviated 40 Eri. It has the Bayer designation Omicron2 Eridani, which is Latinized from ο2 Eridani and abbreviated Omicron2 Eri or ο2 Eri. Based on parallax measurements taken by the Gaia mission, it is about 16.3 light-years from the Sun.

Van Maanen 2, or van Maanen's Star, is the closest known solitary white dwarf to the Solar System. It is a dense, compact stellar remnant no longer generating energy and has equivalent to about 68% of the Sun's mass but only 1% of its radius. At a distance of 14.1 light-years it is the third closest of its type of star after Sirius B and Procyon B, in that order. Discovered in 1917 by Dutch–American astronomer Adriaan van Maanen, Van Maanen 2 was the third white dwarf identified, after 40 Eridani B and Sirius B, and the first solitary example.
Gliese 436 is a red dwarf located 31.9 light-years away in the zodiac constellation of Leo. It has an apparent visual magnitude of 10.67, which is much too faint to be seen with the naked eye. However, it can be viewed with even a modest telescope of 2.4 in (6 cm) aperture. In 2004, the existence of an extrasolar planet, Gliese 436 b, was verified as orbiting the star. This planet was later discovered to transit its host star.
Doris Daou is a Lebanese-born Canadian-American astronomer who was formerly the Director for Education and Public Outreach of the NASA Lunar Science Institute and the associate director of the NASA Solar System Exploration Research Virtual Institute (SSERVI), and is currently the program contact for NASA's "Small Innovative Missions for Planetary Exploration (SIMPLEx)".
Rebecca Oppenheimer is an American astrophysicist and one of four curator/professors in the Department of Astrophysics at the American Museum of Natural History (AMNH) on Manhattan's Upper West Side. Oppenheimer is a comparative exoplanetary scientist. She investigates planets orbiting stars other than the Sun. Her optics laboratory is the birthplace of a number of new astronomical instruments designed to tackle the problem of directly seeing and taking spectra of nearby solar systems with exoplanets and studying their composition, with the ultimate goal of finding life outside the solar system.
Gliese 440, also known as LP 145-141 or LAWD 37, is an isolated white dwarf located 15.1 light-years from the Solar System in the constellation Musca. It is the fourth closest known white dwarf to the Sun, after Sirius B, Procyon B, and van Maanen's star.
Nicholas B. Suntzeff is an American astronomer and cosmologist. He is a University Distinguished Professor and holds the Mitchell/Heep/Munnerlyn Chair of Observational Astronomy in the Department of Physics & Astronomy at Texas A&M University where he is Director of the Astronomy Program. He is an observational astronomer specializing in cosmology, supernovae, stellar populations, and astronomical instrumentation. With Brian Schmidt he founded the High-z Supernova Search Team, which was honored with the Nobel Prize in Physics in 2011 to Schmidt and Adam Riess.
RX Andromedae is a variable star in the constellation of Andromeda. Although it is classified as a dwarf nova of the Z Camelopardalis (UGZ) type, it has shown low-luminosity periods typical of VY Sculptoris stars. However, for most of the time it varies from an apparent visual magnitude of 15.1 at minimum brightness to a magnitude of 10.2 at maximum brightness, with a period of approximately 13 days.
WD 0806−661, formally named Maru, is a DQ white dwarf with an extremely cold Y-type substellar companion, located in the constellation Volans at 62.7 light-years from Earth. The companion was discovered in 2011, and is the only known Y-type companion to a star or stellar remnant. At the time of its discovery WD 0806-661 B had the largest actual and apparent separation of any known planetary-mass object, as well as being the coldest directly imaged substellar object then known.

Debra Meloy Elmegreen is an American astronomer. She was the first woman to graduate from Princeton University with a degree in astrophysics, and she was the first female post-doctoral researcher at the Carnegie Observatories.
Laura Ferrarese is a researcher in space science at the National Research Council of Canada. Her primary work has been performed using data from the Hubble Space Telescope and the Canada-France-Hawaii Telescope.
SU Ursae Majoris, or SU UMa, is a close binary star in the northern circumpolar constellation of Ursa Major. It is a periodic cataclysmic variable that varies in magnitude from a peak of 10.8 down to a base of 14.96. The distance to this system, as determined from its annual parallax shift of 4.53 mas, is 719 light-years. It is moving further from the Earth with a heliocentric radial velocity of +27 km/s.
Kevin France is an astrophysicist and assistant professor in the Department of Astrophysical and Planetary Sciences at the University of Colorado. His research focuses on exoplanets and their host stars, protoplanetary disks, and the development of instrumentation for space-borne astronomy missions.
BZ Ursae Majoris is a dwarf nova star system in the northern circumpolar constellation of Ursa Major. It consists of a white dwarf primary in a close orbit with a red dwarf. The latter star is donating mass, which is accumulating in an accretion disk orbiting the white dwarf. The system is located at a distance of approximately 505 light years from the Sun based on parallax measurements.
Ata Sarajedini is an astrophysicist, professional astronomer, academic, author, and podcaster. He is the Bjorn Lamborn Endowed Chair and Professor in Astrophysics at Florida Atlantic University.