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. Since we know that large crystals need time to grow, the magma must have spent some time deep underground.