That is, if you observe the spectrum of a star and can determine the wavelength where the emission peaks (Î»max), you can calculate that starâs temperature. Here is another copy of the plot that we studied in Lesson 3: Figure 4.1: Two-dimensional plot of the spectrum of a blackbody with different temperatures.
Igneous rocks usually contain the most crystals. The longer it takes the magma to cool, the larger the crystals.
Similarly, a rock with small crystals probably formed at or near the surface and cooled quickly. These are called extrusive rocks and have an aphanitic texture (from the Greek a- meaning not, and phanerous). And some magma cools so quickly that no crystals form; we say that these have a hyaline texture (from the Greek hyalis meaning glass). Sometimes, a rock will contain both aphanitic and phaneritic crystals in it. This means that something truly odd happened to the magma before it was erupted.