It's not yet Rosh Chodesh (Jewish new month), or even very near it, but I'll probably forget to post this next week when it'll be relevant. So:
Spotting the new moon is really difficult.
In mishnaic times, they established the new month by having witnesses come to the central court and testify that they'd seen the new moon. There are all sorts of leniencies, which I don't remember accurately offhand and it's nearly Shabbat, to enable witnesses to get to the court as quickly as possible. I do remember being awfully surprised that there should be leniencies, because surely there would be plenty of witnesses right there in Jerusalem.
So - click through to the big version of the picture - now I know why; seeing the new moon is hard.
Here's an article about why it's hard, apart from its being awfully little.
I'm inspired to go and learn about how Islam manages, because Islamic religious calendars often have a disclaimer that months are subject to the sighting of the new moon, and what do they do when you really can't see it? So I'm reading Moonsighting.com, which is very interesting, although I don't understand most of it. Any Muslim lurkers on this blog, now would be a good time to say hello...