Selections from The International Year of Astronomy poster series by Simon C. Page
Posts tagged astronomy
Cecilia Payne-Gaposchkin (May 10, 1900 – December 7, 1979) was an English-American astronomer and astrophysicist who in 1925 proposed in her PhD thesis an explanation for the composition of stars in terms of the relative abundances of hydrogen and helium.
In 1925 she became the first person to earn a Ph.D. in astronomy from Radcliffe College (now part of Harvard). Her thesis was “Stellar Atmospheres, A Contribution to the Observational Study of High Temperature in the Reversing Layers of Stars”. Astronomer Otto Struve called it “undoubtedly the most brilliant Ph.D. thesis ever written in astronomy”.
Payne was able to accurately relate the spectral classes of stars to their actual temperatures by applying the ionization theory developed by Indian physicist Meghnad Saha. She showed that the great variation in stellar absorption lines was due to differing amounts of ionization at different temperatures, not to different amounts of elements. She correctly suggested that silicon, carbon, and other common metals seen in the Sun’s spectrum were found in about the same relative amounts as on Earth, but that helium and particularly hydrogen were vastly more abundant (for hydrogen, by a factor of about one million). Her thesis thus established that hydrogen was the overwhelming constituent of the stars (see Metallicity).
When Payne’s dissertation was reviewed, astronomer Henry Norris Russell dissuaded her from concluding that the composition of the Sun is different from that of the Earth, contradicting the accepted wisdom at the time. However, he changed his mind four years later after deriving the same result by different means. After Payne was proven correct, Russell was often given the credit, although he himself acknowledged her work in his paper.
A star cluster once thought to be part of the spectacular Orion Nebula is actually a separate celestial entity parked in front of the nebula, a new study reveals.
Scientists using the Canada-France-Hawaii Telescope in Hawaii found that the star cluster NGC 1980 is a distinct, massive bunch of stars in front of the Orion nebula, which at a range of 1,500 light-years is Earth’s closest known star factory. The cluster is huddled unevenly around the star iota Ori at the southern tip of the sword in the famed Orion constellation.
The star cluster is a slightly older sibling of the Trapezium cluster at the center of the Orion Nebula, the researchers say. And the findings suggest a cosmic structure that astronomers have been calling the Orion Nebula Cluster is actually a complicated mix of these two star clusters.
“For me the most intriguing part is that the older sibling, the iota Ori cluster, is so close to the younger cluster still forming stars inside the Orion nebula,” study researcher João Alves, of the University of Vienna, said in a statement.
Alves and his colleagues combined observations of the Orion nebula by the MegaCam imager on the Canada-France-Hawaii Telescope with past studies using ground-based and space observatories to make the discovery.
The Flame Nebula, designated as NGC 2024 and Sh2-277, is anemission nebula in the constellationOrion. It is about 900 to 1,500light-years away.
The bright starAlnitak (ζ Ori), the easternmost star in the Belt of Orion, shines energetic ultraviolet light into the Flame and this knocks electrons away from the great clouds of hydrogen gas that reside there. Much of the glow results when the electrons and ionized hydrogen recombine. Additional dark gas and dust lies in front of the bright part of the nebula and this is what causes the dark network that appears in the center of the glowing gas. The Flame Nebula is part of theOrion Molecular Cloud Complex, astar-formingregion that includes the famousHorsehead Nebula.