If you are using a monospaced font like courier, use two spaces after a period. Anything else, use 1.
It used to be 2, but it has officially changed to one. I agree with Kim about that font, though -- it is font & sizing related.
But it did officially change. I was also taught two. Now I only use one when I sent articles in to websites & such.
Most modern computer fonts (the notable exceptions seem to be everything our lawyers at work use, LOL!) automatically put extra space behind a period so there is not only no need to put two spaces, but putting two spaces makes it look like there's too much space. For most computer work, you only put one space. If you're on a real typewriter, or using one of the monospace fonts, then you put two spaces.
It's easy enough to fix if you realize your mistake. Just do a search & replace for ". " and replace them all with ". " and you're good to go.
70% of the U.S. population now lives in a state where same-sex marriage is legal. At 36 and counting!
Also, you get used to it. I was definitely raised with the "two spaces" rule but I have adjusted and now it's effortless.
If it makes you feel any better, Bonita, I still put two spaces after a period often, just out of habit. While i do agree that 1 space is correct, the truth is I really don't care all that much day to day, therefore have never made a very deliberate effort to change my habits
ETA: And on the internet, browsers get rid of your extra spaces anyway. For example, i put about 17 spaces between the word get and rid in the previous sentence, but when it renders in your browser, you just see one space
Cecilia Marie 1/10/10
Photo By Anne Schmidt Photography
It changed to one space when I was getting my thesis for my bachelors.. that was a tricky thing to learn!
DH-Aug 30th 1997 Josiah - 6/3/02 Isaac 7/31/03