Add some constants

Author: Jorge

src/skaero/constants.py

@@ -0,0 +1,13 @@
+"""
+Mathematical and physical constants
+"""
+
+from skaero import units as u
+
+# Earth's mean equatorial radius from IAU Working Group on Cartographic
+# Coordinates and Rotational Elements: 2015
+R_earth = 6.3781366e6 * u.meters
+
+# Standard Earth's gravity acceleration value from "The International System of
+# Units by Barry N.Taylor and Ambler Thompson"
+g0 = 9.80665 * u.meters / u.seconds