[ Optional reading: Mathematically, your exact longitude along with your Time Zone (both measured from Greenwich) and your exact Local Standard Time can be used toĬalculate a number known as your LMST - your Local Mean Sidereal Time. Very important numbers since they, along with the date and time, determine exactly what portion of the sky you can see. So, your Latitude and Longitude on Earth are two If you move South you get to look at things that more northern observers cannot see. If you move West you get to look at things that have already set at this location. If you move East you get to lookĪt things that haven't risen yet at this location. We'll talk about "Lower Culmination" later.)Īlso - if you move to a different spot on the Earth, you get a slightly different view of the sky. (When an object reaches this highest point in the sky we say it is at its Upper Culmination This is why it is important to choose a site with aĬlear southern horizon in step 1. Everything on your Meridian has therefore reached its highest point in the sky tonight, and is thereforeĪt its best for viewing since it is as far as it can be away from the (murky) horizons. Everything in the sky left of your Meridian is rising and everything right of your Meridian is setting For instance in most of North America, during Daylight Saving Time, the Standard time is one hourĬlick: NRC or Canadian Geographic Magazine for more information on Canadian Time Zones.Ĭlick: CIA or USNO for more information on World time zones.ĭirectly South of you, curving from the South point on the horizon up to the Zenith, is an imaginary line in the sky known as It is then up to you to know the local regulations concerning Daylight Saving Time in order toĬome up with the Local Standard Time. In the Western Hemisphere are specified as negative numbers so, for instance, Calgary is at (roughly) -114° Longitude.)Ĭan tell you the exact time. Your Longitude West or East of Greenwich, England is measured in degrees from 0° to 180°. These are important becauseĪs the Earth rotates on its axis every 24 hours and also as it revolves around the Sun every year, everything "up there" moves.Ī good, high-resolution topographical map or a GPS receiver can tell you where you are. The next step is to know where you are and the current date and Local Standard Time. Would actually be behind you in the Northern sky, and so it is not visible in this view.Ī "right side view" of the diagram above, In this diagram (for mid-northern latitudes), Polaris Note that this is not the position of Polaris - the Pole Star. There is one more point of interest to the observer - the point directly above you (straight "up") which is called the Note that the observer is looking South, with East to your left, West to your right, and North behind you.Īlthough we know the sky forms a complete dome over the observer, I will only show the "southern" half of the view in these diagrams The diagram at left will be used to show the observer (you) and your telescope at such a site on a clear dark night. It usually means one with a relatively clear horizon, especially towards the South. The first step in any observing session is to pick a safe observing site, and for us in the Northern Hemisphere, Use these links to go directly to a topic, or you can read all of them by scrolling from top to bottom. This web page is designed to assist the beginning astronomer in understanding these terms, and how to apply them, just asĪmateur and professional astronomers the world over use them to find everything in the night sky. Their own motion across the background of stars, so for all these objects their sky position changes hourly or daily butĪll the textbooks, star charts, planispheres and "GOTO" computers refer to sky position coordinates - calledīut What are they?, Why are they necessary? and, How can you visualize them on the night sky? Interested in Astronomy? Become a member of the RASC!Ĭlick here to find out about RASC membership and RASC publications.Įvery star, cluster, nebula, galaxy, radio source, and quasar has a position in the night sky.Īll the Solar System objects - the Sun, the Moon, the other planets, asteroids, and comets have RASC Calgary Centre - A Complete Guide toĬopyright © 2005- Larry McNish - All rights reserved.
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