The lunar crater Aristarchus ( on the NW edge of the Oceanus Procellarum). This huge, circular crater is 25 miles (40 km) in diameter and 2.2 miles (3.6 km) deep (from rim to floor). There is a lot of ejecta (material thrown from the crater at impact) surrounding the crater.

They are remnants of collisions between a comet and asteroid or moon and meteorite. They hit  the moon at different velocities but the average speed is 12 miles per second or 20 Km in second.The moon's Surface influenced by millions of impact craters .As moon has no atmosphere to protect it from this bombardment and there is no erosion (wind or water), and also geologic activity in moon is little,  therefore these craters remain up till another impact changes them.

Ptolemaeus is the large (diameter=164 km ) flat-floored crater at the top. Alphonsus (diameter = 108 km) is at the lower left and Albategnius crater (diameter = 114 km) is at lower right.

These craters are much different in size may be are flooded by lava and only some of them are visible . Low levels of surface like seas have fewer craters than other oreas because they formed more recently and had less time to get hit. Due to remanants of ancient craters many rupes or lines of mountainous, cliffs came to exist one of them is Rupes Altai a mountain rang with 315 miles (50km) longitude on the moon.

                       Different Types of impact craters                      

The crates are different in size, shape and complexity and this is due to difference in size, mass, speed and angle of falling objects.As small and slow objects have less energy they make small and simple crater,s but very large impacts can even make secondary craerting and also ejected material when back to ground and make new smaller craters.

Most of the craters are circle in shape and few of them are non circular like Messier and Messier A (left picture). About mare fecunditatis scientist could not find how these oddly shape crates could origin form.

Complex Crater Euler crater, a complex crater with a diameter of 17 miles (28 km) and a depth of 1.5 miles (2.5 km).

Simple Crater Moltke crater, a simple crater with a diameter of 4.3 miles (7 km).

Most craters with less than 15 kilometers diameter have bowl like shape.Crater with diameter more than 15 kilometers get more complicated forms which can be divided to shallow, flat floors compose of solid lava, central uplifting that can have one peak or more  a ring and terraces on inner walls.

                                   Simple impact craters:                               

These craters are bowl shape with smooth walls, and mostly with a diameter less than 9 miles (15 km). and depth about %20 of their diameter.

                                  Complex Impact craters:                           

This type of craters got single peak or more peaks in the middle of the crater and their diameters ranges from 12 to 110 miles (20 to 175 km).

Their central uplift often got one peak or a few peaks craters that have diameter greater than 110 miles (175 km). They are more complex and they got ring – shap uplifts within the crater.

                                            Impact Basin:                                      

This is a impact crater with rim diameter over 185 miles (300 km) and more than 40 such basins exist on the moon and they cause crust deformations and material which ejected from them distributed over wide regions.

The lunar basin Schrodinger is 200 miles (320 km) in diameter. Schrodinger also has an inner ring which is 92 miles (150 km) in diameter and about 75 percent complete. Schrodinger is one of the youngest impact basins on the Moon.

 

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