As for the rest, Uranus was discovered in 1781 by William Herschel, Neptune was discovered in 1846 by Galle and d'Arrest, and Pluto was discovered by Tombaugh in 1930. I'm not sure which was the last one discovered - many have been discovered recently . Yes, many other solar systems have been discovered. Galileo first used a telescope to look at the planets in the early 1600's. 5. Galileo Galilei 6.
Gravity is the force that keeps the planets in orbit around the Sun .
Stars closer to the horizon appear to twinkle more than stars that are overhead - this is because the light of stars near the horizon has to travel through more air than the light of stars overhead and so is subject to more refraction. As stated in our privacy policy , we fully respect your privacy and will not use your e-mail address for any purpose other than the newsletter subscription. Search the Web with our sponsor, Overture. Search the Web. Search the Web with our sponsor, Overture.