Today is the fiftieth anniversary of the launch of the United States’ first satellite, Explorer I. For you space junkies, Rand Simberg has a piece about that and a lot more up at Pajamas Media today.

UPDATE: Oops. Yesterday was the Explorer I anniversary, today is the anniversary of Columbia shuttle disaster five years ago. Not nearly as positive a milestone, but also worth remembering…

UPDATE II — A reader writes in:

Depends upon your time zone. Satellite orbits are catalogued in Universal (Greenwich Mean) Time, and by that measure the launch occurred at 03:48 UTC on 1958-02-01. I described this in my own commemorative post.
NASA’s own “Astronomical Picture of the Day” also chose to post their commemoration on February 1st, although the text cites the date in local time at the launch site.
The announcement of the success was withheld until radio transmissions from the satellite were received in California, confirming that it was, indeed, in orbit. With an orbital period of 114 minutes, this would already have been on February 1st at the launch site in Florida.