We live in the Milky Way galaxy, a fairly typical open spiral galaxy galaxy (Type S, for you naming geeks out there). Those spirally bits spread out from the galactic core, and the whole thing is slowly (quickly) rotating, making one turn every 120 million years or so.
Well, we once thought there were four arms to the Milky Way; now we think there are only two. Regardez la photo:
We’re on a mini arm called the Orion Spur. Here’s a honking big image – you might be able to see better there.
From the MSNBC site that brought me the story (there’s more to read, so click through and take a look):
For decades, astronomers have pictured our galaxy as sporting four major, spiral arms, however new images effectively sever two appendages, revealing the Milky Way has just two major arms.
“We’re not proposing that they change the positions of the arms,” said Robert Benjamin of the University of Wisconsin, Whitewater. “What we’re proposing is a change in the emphasis of the arms.” Benjamin will present his team’s results today here at a meeting of the American Astronomical Society (AAS).
The Milky Way debuted as a spiral celebrity in 1951 when astronomical morphologist William Morgan of the Yerkes Observatory presented his results showing the galaxy’s three arms of hot stars, which he were then named Perseus, Orion and Sagittarius.
“Those were the first three arms of the spiral galaxy,” Benjamin told SPACE.com. “Actually, he got a standing ovation at the AAS meeting, which is something I’ve never seen.”
This is what 19th century astronomy William Herschel thought we looked like:
BTW – it’s -20C on Mars today. That’s a high temperature.
