Regions of stars and interstellar matter that extend from the center of spiral galaxies, forming a spiral pattern; in the Milky Way, these include the Orion Arm where our Solar System resides.
Source: esa.int

09/01/2010

26/12/2009

27/11/2009

17/10/2009

19/09/2009

27/07/2009

06/06/2009

29/05/2009

26/05/2009

14/04/2009

28/02/2009

29/12/2008

27/09/2008

13/09/2008

24/08/2008

15/08/2008

17/07/2008

11/07/2008

22/06/2008

14/06/2008

06/06/2008

30/04/2008

17/04/2008

29/03/2008

25/03/2008

24/01/2008

09/01/2008

05/01/2008

01/12/2007

24/07/2007