It's a phrase I've heard for years, my grandparents and parents said it and now I say it but what does the phrase "once in a blue moon" actually mean? I've always heard it used in reference to something that happens very rarely. For the most part that is true.

When you have 2 full moons occurring within the same month, the second full moon is referred to as the blue moon. It doesn't mean the moon actually turns blue although it can at times take on a blueish hue due to volcanoes or forest fires.

The definition as we know it today first came into use in the late 1940's. A blue moon occurs maybe 4-5 times every 100 years, so it actually does mean, very rarely.

The month of August this year will have 2 full moons meaning we will see a "blue moon". The first full moon of the month will occur on August 1st, the second will be on August 31st. The next time you will see a "blue moon" will not be until 2015 and will occur July 1st and 31st.

So now you know what the famous and widely used phrase "once in a blue moon" means and you can use it accordingly and wisely.

Now go out and impress others with your new found knowledge!