Chances are the lake closest to you is a freshwater lake. But some lakes are extremely salty. These are called saline lakes. Although freshwater lakes often have minor amounts of dissolved salts in them (less than 1-3 g/L), saline lakes have more than this (between 3 and 300g/L).
Astronomical Unit (A.U.). An astronomical unit (A.U.) is the average distance between the Earth and the Sun, which is about 93 million miles or 150 million kilometers.Astronomical units are usually used to measure distances within our solar system.ne kiloparsec (kpc), is one thousand parsecs. One megaparsec (Mpc) is one million parsecs. SUMMARY 1 Astronomical Unit (A.U.) is the average distance between the Sun and the Earth. 1 A.U. = 93 million miles = 150 million kilometers 1 light-year (ly) is the distance that light travels in one year in a vacuum.
The average distance is approximately 225 million km ( or 1.50403 AU). The Earth has a shorter orbital period than Mars, it passes in between Mars and the Sun approximately every 780 days, or 2 years and 50 days. At that time , Mars is seen in the opposite direction from the Sun, at opposition. The time interval between Marsâ opposition and its least distance to Earth can be as large as 8 and a half days. In 2001, for example, opposition took place on June 13 but least distance was on June 21. Each opposition is followed by a very similar one 79 years later.