Instructions
Check the phase of the moon, as well as the times for the rising and setting of the moon on your chosen date. A full moon can cast enough light to obscure many dim stars. A new moon is best, but you can also plan for your stargazing to take place before the moon rises or after it sets.
Check the weather forecast to see if clouds are predicted. Even the clear patches of a partly cloudy sky are likely to be hazier than a completely clear sky.
Note the predicted humidity in the weather forecast. The more humid it is, the hazier the sky will be, and the fewer stars you will see.