Chemical element isotopes: specifically the elements without any stable isotopes are technetium (atomic number 43), promethium (atomic number 61), and all observed elements with atomic numbers greater than 82. Of the 80 elements with at least one stable isotope, 26 have only one single stable isotope. The mean number of stable isotopes for the 80 stable elements is 3.1 stable isotopes per element. The largest number of stable isotopes that occur for a single element is 10 (for tin, element 50). The mass number of an element, "A", is the number of nucleons (protons and neutrons) in the atomic nucleus. Different isotopes
SN 2002cx similar to other type Ia supernovae before 5 days after max, although it is somewhat redder. After 5 days after max SN 2002cx gets progressively redder, although still slightly bluer than SN 1991bg. At 25 days after max SN 2002cx continues to redden, while SN 1991bg starts to get bluer. SN 2002cx's V – I color is red for all times, only slightly bluer than SN 1991bg before 25 days after max, and redder after 25 days after max. SN 2002cx SN 2002cx is a peculiar type Ia supernova. It was discovered in May 2002 by a team of researchers