1. A computer-implemented method performed by data processing apparatus, the method comprising: receiving a first query and a plurality of second queries, each of the first and second queries including one or more terms; determining a temporal correlation score between the first query and each second query, the determination of the temporal correlation score between the first query and each second query being based on a comparison of a temporal series of occurrences of terms of the first query in a first textual corpus comprising news articles and a temporal series of occurrences of terms of the second query in a second different textual corpus comprising blog entries, wherein the comparison is based on news articles and blog entries having timestamps in a same time period; computing a similarity score for the first query and each second query, the similarity score between the first query and a second query being computed based on the temporal correlation score between the first query and the second query; and ranking the plurality of second queries in an order according to their respective similarity scores.