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--- courses:ast201:1 [2023/10/02 00:35] – [5.1 Stellar aberration] asad
+++ courses:ast201:1 [2023/10/02 00:45] (current) – [4. Newton and Einstein] asad
@@ Line 72: / Line 72: @@
 Newton made gravity the physical reason behind planetary motions as opposed to Descartes' mysterious vortices. The full form his gravitational acceleration
-$$ g = \frac{GM}{r^2} $$
+$$ \vec{g} = \frac{GM}{r^2} \hat{r} $$
-and the gravitational potential
+where $G$ is the Newtonian gravitational constant, $M$ the mass of an object and $r$ is the distance at which the acceleration is being calculated. This $\vec{g}$ can be thought of also as a gravitational field around a massive object. The gravitational potential
 $$ U = - \frac{GMm}{r} $$
 for a small mass $m$ around a large mass $M$.
+The theory was later modified by Einstein as
+$$ G_{\mu\nu} + \Lambda g_{\mu\nu} = \kappa T_{\mu\nu} $$
+where $G_{\mu\nu}$ is the [[bn:Einstein tensor]], $g_{\mu\nu}$ is the metric tensor, $T_{\mu\nu}$ is the stress-energy tensor, $\Lambda$ is the cosmological constant and
+$$ \kappa = \frac{8\pi G}{c^4} $$
+is the Einstein gravitational constant.
 ===== - Stellar aberration and parallax =====