Astronomy Index

Locating Astronomical Objects

Angular distance estimation

Facility with finding objects in the night sky takes practice. Here are some tips for building up speed:

  1. Watch the sky. Notice how it changes from hour to hour, night to night and month to month.
  2. Learn how to estimate angular distances. Notice the angular dimensions of various constellations.
  3. Get to know the names and outlines of some constellations. Start with familiar constellations: The Southern Cross, Orion (the Saucepan), Scorpius, Sagittarius (the Teapot) Become adept at finding them as the sky changes during the night and with the seasons. Notice which constellations the Planets are in and how they move through them.
  4. Obtain a planisphere for your latitude. A planisphere is a crude map of the whole sky with a rotating insert that assists you to relate the stars visible at any one time to the rotation and the orbital motion of the Earth. Take it outside at night and hold it above your head to match the sky. A red headlight will allow you to use it in the dark.
    Binoculars with 7 to 10 magnifications, 40 to 50 mm objective lenses and 6° to 7° fovs are suitable for astronomy. If you are buying a pair, try them out at night before hand or obtain a return if not satisfactory agreement - some units have severe internal reflections and display several images of bright objects. They are useless for astronomy.
  5. Obtain a pair of binoculars. Be aware of their field of view (fov), a measure of how much of the sky they display - a larger fov shows more sky. Learn to 'hop' between the brighter stars of constellations without taking them from your eyes. Start with the stars of the Southern Cross, for example. Notice the extraordinary number of stars that becomes visible through them.
  6. Obtain a PC Planetarium Program. Stellarium is excellent, free software to start with. It displays all the stars that can be seen by naked eye, in binoculars and small telescopes. It models the movement of the planets and their moons. It can be set to show the sky from any location on Earth or from any time for thousands of years forwards and backwards in time.
  7. Obtain a star atlas, or print out charts from your Planetarium program.
  8. Obtain a telescope. Become familar with its set up and aligment. Become familiar with the fov of each of your eyepieces. Learn how to point it at brighter stars. Learn how to reach fainter targets by hopping from star.

Last updated: August 2007
Michael Gallagher