Before I start, I'll just mention a little safety tip - DO NOT LOOK AT THE SUN.

Mercury will be passing between the Earth and the Sun today. It'll appear as a tiny dot taking 5 hours or so to cross the whole solar disc.

It'll kick off at 19:12 (UTC) and end at 00:10 (UTC). That's 11:12 Pacific time.

From the BBC:

Mercury transit

The Sun is below the horizon then for myself and a lot of other people so we won't be watching this one.

From NASA:

Mercury transit

To safely observe the transit you need to:
1) Never ever look at the Sun.
2) Use a pair of binoculars or a telescope to project the image of the Sun onto a piece of card or paper (like here on my Venus transit page).
3) Definitely never look at the Sun through binoculars or a telescope, it'll be game over for your vision.
4) If you've got quite a large telescope, or one with a lot of plastic in it, avoid keeping it pointed at the Sun for prolonged periods as it will heat up.

If you don't have binoculars or a telescope you might try using pinhole projection like so:

Pinhole projection

It'll probably be quite hard to see Mercury with this method but worth giving it a try.

Tip for school kids: If it's going on while you're at school tell the teacher and see if you can get the class out of lessons to view it.