{ "cells": [ { "cell_type": "markdown", "id": "2983c76d-aad1-4098-8210-605ad2872370", "metadata": {}, "source": [ "# Radio Astronomy" ] }, { "cell_type": "markdown", "id": "c72fbafd-e4cc-4508-bea2-653e33e8e46a", "metadata": {}, "source": [ "## Interferometry" ] }, { "cell_type": "markdown", "id": "78887e4e-26ec-481c-94eb-db59e13a64bd", "metadata": {}, "source": [ "We finished our discussion last week by looking at how interferometry works. With this method, the condition required for two sources to be resolved is that the difference in the additional path length photons must travel to reach the second telescope is $c \\Delta t \\sim \\lambda$, such that the photons from the source which is $\\Delta \\theta$ away from source which is on axis are still arriving in phase and may be combined coherently. We also expressed this condition as $\\Delta \\theta = \\frac{\\lambda}{L}$, where L is the separation of the telescopes (also known as the baseline).\n", "\n", "We only considered two dishes, but radio interferometers are typically composed of multiple dishes so that the image can be properly sampled, and this phase difference must be measured for every pair of telescopes, which is why the computational cost of this technique quickly increases as you add more baselines to the array.\n", "\n", "As examples, consider the Very Large Array - this is an array of 27 dishes, each 25 m in diamater, in New Mexico. The dishes can be repositioned to change the baselines, with the largest baseline being 37 km." ] }, { "cell_type": "markdown", "id": "6b900a4d-e2c0-4251-94f3-b1473d6fa6bf", "metadata": {}, "source": [ "