The first series, hosted by James Silvester, originally aired from late-2008 through mid-2009. This site contains a some of my favourite episodes from series 1.
Astrarium is now proudly part of the Brachiolope Media Network, check out the network for other great science podcasts, such as:
The awesome physics podcast (by my good friend Ben Tippett) called The Titanium Physicists Podcast. The podcast which can be found here