by MuluTrail89 » Fri Jun 29, 2018 2:39 pm
neufer wrote: ↑Fri Jun 29, 2018 11:46 am
MuluTrail89 wrote: ↑Fri Jun 29, 2018 5:22 am
"...a view of the distant stars in the Sagittarius spiral arm...." I may be out of date, but I've always remembered being taught that when we look at the summer Milky Way from our position in the Orion Spur we're looking across a gulf of 3,000-3,500 L.Y. to the Sagittarius Arm. Then when we look at its Small Sagittarius Star Cloud we're peering through a gap (window) in its obscuring dust clouds and seeing the next arm inward toward the Galactic Core: the Scutum-Centaurus Arm, and a region in it of rapid star formation with many supergiants, all at 10,000-12,000 L.Y. distant.
https://en.wikipedia.org/wiki/Scutum%E2%80%93Centaurus_Arm wrote:
<<The Scutum–Centaurus Arm, also known as Scutum-Crux arm, is a long, diffuse curving streamer of stars, gas and dust that spirals outward from the proximate end of the Milky Way's central bar. The Milky Way has been assumed since the 1950s to have four spiral arms although the evidence for this has never been strong. In 2008, observations using the Spitzer Space Telescope failed to show the expected density of red clump giants in the direction of the Sagittarius and Norma arms. In January 2014, a 12-year study into the distribution and lifespan of massive stars and a study of the distribution of masers and open clusters both found evidence for four spiral arms. The Scutum–Centaurus Arm lies between the minor Carina–Sagittarius Arm and the major Perseus Arm. The Scutum–Centaurus Arm starts near the core as the Scutum Arm, then gradually turns into the Centaurus Arm.
The region where the
Scutum–Centaurus Arm connects to the bar of the galaxy is rich in star-forming regions. In 2006 a large cluster of new stars containing 14 red supergiant stars was discovered there and named RSGC1. In 2007 a cluster of approximately 50,000 newly formed stars named RSGC2 was located only a few hundred light years from RSGC1. It is thought to be less than 20 million years old and contains 26 red supergiant stars, the largest grouping of such stars known. Other clusters in this region include RSGC3 and Alicante 8.>>
Thank you, Neufer. This seems to confirm what I was taught, which was that when I look through the dust gap sometimes called the Small Sagittarius Star Cloud the view is inward toward the Galactic Core and 10,000 l.y. away stars of the Scutum-Centaurus Arm are viewed, not stars of the Sagittarius Arm as stated in the APOD text. Except that in my day we just called it the Centaurus Arm. The scale of the graphic you posted was especially helpful to show Scutum-Centaurus at the distance from the sun that I remembered. And what we called the Orion Spur (our home!) is now the Orion-Cygnus Arm. So many of the names have changed since five decades ago! At least on this modern graph the name of the Perseus Arm remains the same.
Thanks again.
[quote=neufer post_id=283697 time=1530272782 user_id=124483]
[quote=MuluTrail89 post_id=283691 time=1530249743]
"...a view of the distant stars in the Sagittarius spiral arm...." I may be out of date, but I've always remembered being taught that when we look at the summer Milky Way from our position in the Orion Spur we're looking across a gulf of 3,000-3,500 L.Y. to the Sagittarius Arm. Then when we look at its Small Sagittarius Star Cloud we're peering through a gap (window) in its obscuring dust clouds and seeing the next arm inward toward the Galactic Core: the Scutum-Centaurus Arm, and a region in it of rapid star formation with many supergiants, all at 10,000-12,000 L.Y. distant.
[/quote][quote=" https://en.wikipedia.org/wiki/Scutum%E2%80%93Centaurus_Arm"]
[float=left][img3=""]https://upload.wikimedia.org/wikipedia/commons/thumb/a/a7/Milky_Way_Arms_ssc2008-10.svg/500px-Milky_Way_Arms_ssc2008-10.svg.png[/img3][/float]<<The Scutum–Centaurus Arm, also known as Scutum-Crux arm, is a long, diffuse curving streamer of stars, gas and dust that spirals outward from the proximate end of the Milky Way's central bar. The Milky Way has been assumed since the 1950s to have four spiral arms although the evidence for this has never been strong. In 2008, observations using the Spitzer Space Telescope failed to show the expected density of red clump giants in the direction of the Sagittarius and Norma arms. In January 2014, a 12-year study into the distribution and lifespan of massive stars and a study of the distribution of masers and open clusters both found evidence for four spiral arms. The Scutum–Centaurus Arm lies between the minor Carina–Sagittarius Arm and the major Perseus Arm. The Scutum–Centaurus Arm starts near the core as the Scutum Arm, then gradually turns into the Centaurus Arm.
The region where the [url=https://upload.wikimedia.org/wikipedia/commons/a/a7/Milky_Way_Arms_ssc2008-10.svg]Scutum–Centaurus Arm[/url] connects to the bar of the galaxy is rich in star-forming regions. In 2006 a large cluster of new stars containing 14 red supergiant stars was discovered there and named RSGC1. In 2007 a cluster of approximately 50,000 newly formed stars named RSGC2 was located only a few hundred light years from RSGC1. It is thought to be less than 20 million years old and contains 26 red supergiant stars, the largest grouping of such stars known. Other clusters in this region include RSGC3 and Alicante 8.>>[/quote]
[/quote]
Thank you, Neufer. This seems to confirm what I was taught, which was that when I look through the dust gap sometimes called the Small Sagittarius Star Cloud the view is inward toward the Galactic Core and 10,000 l.y. away stars of the Scutum-Centaurus Arm are viewed, not stars of the Sagittarius Arm as stated in the APOD text. Except that in my day we just called it the Centaurus Arm. The scale of the graphic you posted was especially helpful to show Scutum-Centaurus at the distance from the sun that I remembered. And what we called the Orion Spur (our home!) is now the Orion-Cygnus Arm. So many of the names have changed since five decades ago! At least on this modern graph the name of the Perseus Arm remains the same.
Thanks again.