Citation rankings and their interpretation are controversial even in highly structured academic literature; and their cousins in the blogosphere are more open to debate. There is little agreement on how best to rank blogs, especially given that the patterns of links among them change as posts are added, and some blogs play tricks to boost their position. So our list is a snapshot of science blogs and their place in the blogosphere, rather than a definitive ranking.

The Technorati search engine indexes 46.7 million sites and uses a relatively simple measure to create ranks - it uses the number of sites linking to a particular blog in the past six months (with a longer time frame, older blogs would obtain a higher ranking simply from having been around longer). Technorati's approach is useful, but not all encompassing: great blogs with small, devoted audiences do not rate highly.

Putting a blog's URL into the service's Blog Finder provides a ranking. To mine the service for science blogs, Nature reporter Declan Butler compiled a preliminary list of sites known to Nature staff, and supplemented this with those frequently cited by other science bloggers and aggregrators.

We narrowly define science blogs as ones that, as far as can be established, are written by working scientists and are about science (not their cat).

In instances where blogs have recently moved and their old URL has a higher score, we used the latter for ranking, but give the new URL so readers can find it.

To ensure that we did not omit high-ranking science blogs we checked the list with the publicly available Technorati Top 100, and did a Technorati search for blogs containing the keyword 'science'.

But we certainly might have missed a few. If you know of any gaffes, please let us know on our newsblog.