Our sleep is influenced by many factors, most of them are intrinsic. Nonetheless, an important component is yet extrinsic. To be honest, it might even be described as the biggest celestial body, bigger by over one million than earth, with a temperature of more than 27 million degrees (Fahrenheit). Playing an important role in our alertness and sleepiness, the sun is actually the source of synchronizing hormonal secretion processes and circadian rhythms. 

If you find it hard to fall asleep at night or to wake up in the morning, or have any trouble with aligning your day & night, you might want to try increasing your exposure to the sun during the day. Time in the sunlight will simply give your body the opportunity to restart natural rhythm.