The Astrophysics Spectator
The Astrophysics Spectator
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With this issue, we leave the Galactic center and focus instead on the stars close to the Sun. A new page is added to the “Milky Way Galaxy” path that describes the flow of stars within the Galactic disk. A new commentary, the first in nearly a year, is also added with this issue.
The motion of the nearby stars relative to the Sun is a consequence of the orbits of the stars and the Sun around the Galactic center and the motion of Earth around the Sun. Earth's motion reflected in the motion of a nearby star—the parallax of a star—provides us with the best method of deriving a distance to that star. The orbital motion of the nearby stars around the Galactic center provides us with a probe of the local Galactic gravitational field. Eight decades ago, studies of this motion showed that the Galactic disk does not rotate around the Galaxy like a solid disk; the disk was found to rotate differentially with a nearly constant velocity. Today, the observed shear in the average stellar velocity suggests that the Galaxy's spiral arms and central bar are influencing the motion of the stars.
I was shaken from my year-long lethargy and inspired to write a commentary by my young son's fascination with the latest Space Shuttle launch. I grew up in a NASA company town, and without doubt the manned space flight program catalyzed my love of astronomy. I can see in my son my own early fascination with rockets. These grand, powerful machines fire the imagination, especially of a young boy.
Next Issue: The next issue of The Astrophysics Spectator is scheduled for September 5.
Jim Brainerd
The Allure of Manned Space Flight. At one time in the technological vanguard, manned space flight long ago slipped into irrelevance, as the technological forefront passed to computer science and biotechnology. Manned space flight remains frozen in time, but the roar of a rocket rising on a column of fire still has its visceral appeal. (continue)
The Local Motion of the Galaxy. The Galactic disk does not rotate like a solid body; it doesn't even rotate axisymmetrically. The stars in the disk act as a fluid in their motion around the Galactic center. Part of this motion is a differential rotation around the Galactic center, but another part is a radial motion that may be caused by the bar in the center of the Galaxy and the spiral arms flanking the Sun. (continue)
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