It is believed that Thales was born around 625 BC in Miletus (on the coast of present day Turkey.) Thales is credited with being the first Greek philosopher: he was the first to start trying to explain the natural world without the use of Gods. What we know of Thales is due to what other ancient Greek writers said as no original works of Thales survive.
Thales was the first person to use the Little Dipper (Ursa Minor) as a navigation aid. The Little Dipper contains the North Star. The Greeks at the time used the Big Dipper for navigation, but since the Little Dipper contains the North Star (Polaris), it moves less over the course of a night.
He was able to measure the height of a pyramid using the length of its shadow. By waiting until a person's shadow was as equal in length to his height, he marked off the length of the pyramid at this time. The length of the shadow was then equal to the height of the pyramid. He also was able to figure out the distance of a ship to the shore, but it is unclear how he did this.
He is said to have predicted a solar eclipse in 585 BC, but it is questionable if this was really possible for him to do. If he did predict it, no one knows how he did it.