Is Cosmos (1980) obsolete now that Cosmos: A Spacetime Odyssey (2014) has come out?

No: Cosmos (1980) is not obsolete.

This is obviously a very subjective topic, but I'd argue you could (and should!) watch both series.

Firstly, Carl Sagan. The man was simply amazing, with one of the most mesmeric voices imaginable. Watch at least one episode, just to hear it.

Secondly, a lot of the science in the original Cosmos still holds true today. For the parts that don't, the latest editions of the DVDs have added scenes at the end of the episode where Sagan explains how the science has changed since this episode.

Obviously, there are some noticeable changes, such as Pluto no longer being a planet, but largely the fundamental things he covers, such as the age of the universe, the Cosmic Calendar, the achievements of the likes of Tycho Brahe and Joannes Kepler, global warming, the big bang - our understanding of these things has not fundamentally shifted between 1980 and 2014 to an extent that what Saga was saying was incorrect.

Whilst the new series is fantastic, the majority of the changes are aesthetic. The newer animation means some of the historical tales, rather than just showing a presenter on screen narrating and gesticulating, actually show CGI created stories of what the narrator is covering.

In terms of the major differences, I would argue it heavily comes down to the oratory style you prefer.

Sagan had a captivating voice and challenged us to use our imaginations when considering all the evidence. Even when describing the vast size of space, he made it seem a little less scary with his hypnotic voice.

Tyson on the other hand has always had a much more impersonal, revealing oratory style. He addresses things in absolute detail, and is more provocative than Sagan. For example, whilst Sagan never went into detail on his own religious beliefs, Tyson is much more outspoken about his feelings that science should influence politics.

Ultimately, I'd suggest watching both. Start with Sagan's and take your time enjoying them. Then watch Tyson's and see the aesthetic differences (the first episode is very similar otherwise).