- Logic (Wikipedia)
Logic is the study of correct reasoning. It includes both formal and informal logic. Formal logic is the science of deductively valid inferences or logical truths. It studies how conclusions follow from premises due to the structure of arguments alone, independent of their topic and content. Informal logic is associated with informal fallacies, critical thinking, and argumentation theory. It examines arguments expressed in natural language while formal logic uses formal language. When used as a countable noun, the term “a logic” refers to a logical formal system that articulates a proof system. Logic plays a central role in many fields, such as philosophy, mathematics, computer science, and linguistics.
- How to find and observe NGC457 (TOTS#3) (eyesonthesky.com)
NGC 457 is an open cluster within our own Milky Way galaxy. It is over 7,900 light years from Earth, so the photons from it reaching your eye in a telescope left that cluster about the time copper was first being used in the Middle East. The estimated age is about 21 million years, making it one of the younger star clusters in our galaxy. Here is how to locate it.
- NGC 457 (Wikipedia)
NGC 457 (also designated Caldwell 13, and known as the Dragonfly Cluster, E.T. Cluster, Owl Cluster, Kachina Doll Cluster or Phi Cassiopeiae Cluster) is an open star cluster in the constellation Cassiopeia.
