Questions about the Queen Mum & her upcoming ritual celebrations

I just read this article about the Queen turning 86, but the description is confusing to me, so I thought someone could stop in and explain this, so I can understand.
www.wftv.com...

The queen celebrates her birthday twice, with smaller family celebrations on her actual birthday and a second, grander celebration at London's Buckingham Palace on her "official" birthday, which falls this year on June 16.

What's the difference between her actual birthday and her "official" birthday? Why does the date of her "official" birthday fall on a different date every year? Does her "official" birthday follow or procede her actual birthday?

Also, the article states:

This year the queen will also celebrate her Diamond Jubilee to mark 60 years on the throne on the weekend of June 2-5.

Seems as though June 2012 might be an interesting month of rituals and celebrations. Not to forget that the Olympics kick off shortly there after in July.

Thanks in advance to anyone who can answer my questions and clear up my confusion.

The Queen's Official Birthday is a day on which the birthday of the monarch of the Commonwealth is officially celebrated , its generally around the end of May or the start of June .
The Queens actual birthday is on 21 April .

ps ....Down with the Monarchy

reply to post by gortex

The Queens actual birthday is on 21 April

Ah, thank you!

But, I'm still confused by this:

is a day on which the birthday of the monarch of the Commonwealth is officially celebrated , its generally around the end of May or the start of June

When did they start this tradition? I'm wondering what Monarch this officially started with. I'll have to do some digging to see what I can find, but thanks for pointing me in the right direction.

ps ....Down with the Monarchy

I couldn't agree more.