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It is about protons in a atom. We use it for idintify elements.
The Seven Sisters, or The Pleiades, isn't a constellation. It's an open cluster of many, many stars - therefore each one has it's own magnitude. However, the open cluster itself has a combined apparent magnitude of 1.6
Mineral samples can be scraped across the bottom (i.e., the unglazed side) of a tile to create a colour streak which is characteristic of the mineral. Note that it takes more than a colour streak to identify a mineral. Many minerals have the same colour streak. Other characteristics such as the hardness and density will also need to be determined in order to positively identify a mineral.