Tonight is Rosh Chodesh Sivan!
It's the only Rosh Chodesh that has its own niggun. This niggun originated bein hashemashot, in the final minutes of Shabbat overlapping with the initial minutes of Rosh Chodesh Sivan 5759 (Saturday, May 15, 1999). Shavuot was coming on 6 Sivan (Friday, May 21), and Star Wars Episode I: The Phantom Menace was opening on May 19. I was sitting on top of a picnic table in the Quad with my guitar. That evening, in anticipation of the release of Episode I, they were showing the original Star Wars in the Pfoho dining hall. Therefore, this niggun's other name is Tikvah Chadashah. Six years later, even though Anakin Skywalker has turned to the Dark Side, we can still hold out for A New Hope.
Exodus 19 (the account of the theophany that is read on Shavuot) begins "Bachodesh hashelishi" ("in the third month"). Since no day of the month is specified, this is traditionally understood to be on the chodesh, on the first day of the month. [The tractate of the Mechilta containing the midrash on the Ten Commandments is called Masechet Bachodesh, after this first word.] This is the day on which Israel arrived at Sinai. Here we are!