Ok, here it is, once and for all, the proper use of 'it's'.
If the sentence you are writing could be read 'it is' , then it is 'it's'. If you can't read it as 'it is', then it is 'its'.
"It's a beautiful day today!" You can also say, "It is a beautiful day today".
But you would not say, "Its a beautiful day today."
Believe it or not 'Its" is the possessive. Example: "The airplane won't lose its way in the dark."
If you use an apostrophe there, 'it's' you would basically be saying, "The airplane won't lose it is way in the dark."
This is so easy to remember and I can't believe all the places I see it used incorrectly, from emails that friends send me, to professional flyers and documents, and even on TV!
I understand how the 's can make the contracted form look like a possessive, but you know the English language (or maybe you don't!) Why make it simple when you can make it more complicated? There are so many rules to follow but also rules that are broken, like 'i before e except after c, like in receive'. But then there is neighbor and weigh, so we need another rule.
Remember, the possessive forms of personal pronouns never take an apostrophe, while contractions always require one.
Example: The iron left its grim outline on the silk shirt (possessive)
It's a stupid but popular program. (contraction)