The best time to go is in the springtime.  The crowd will be low and it is weather just the right.  Most days the high is 65 - 64 degrees Fahrenheit and the low is between 45-46 degrees Fahrenheit.  The sun will be out most of the time but some days will be cloudy or some days will be wet and rainy.  The weather at night will be a lot cooler than the weather in the day, that is the best time to go out and stare in amazement at the sparkling moon.  Most of the time a breeze is blowing so you should dress warmly.  Have fun!