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“When I look up at the night sky - especially in town - I can only see a few stars... 

Where do I look? What will I see?

We can get you a map of the sky and teach you how to use it:

 The sky is mapped into 88 constellations - mythological “connect the dots” figures of of human and animal characters as well as familiar objects as envisioned by ancient civilization.  Before light pollution, people used the stars as navigational tools as well as reference points for time and season.    The best known and brightest constellation is “ORION - THE HUNTER”  pictured here.  Orion can be seen rising in the late evening during November, and rises about a 4 minutes earlier every night. from mid- Autumn to mid Spring.

Positions on earth are defined by the intersection of  imaginary lines of Latitude and Longitude. These lines serve the same purpose as  naming and numbering streets so that we can define and locate a specific location in town.

The Latitude at the Equator is 0 degrees; all latitude lines are parallel and run east -west.    In Tulsa, we are at 36 degrees North. At +90 degrees (North Pole) and -90 degrees (South Pole) the imaginary lines that circle the globe shrink in size to single points.   Latitude indicates our position relative to the Equator and the nearest Pole. At lower Latitudes, the sun is always higher during the day for warmer climates; at higher latitudes the sum is always lower and the climate is cooler.  

All Longitude lines come together at the poles and indicate east to west position not primarily by miles, but by time. The “O”  Longitude line (Prime Meridian) passes from North to South Poles through the Royal Observatory in Greenwich, UK  Tulsa’s longitude is  96 degrees west so we see sunrise six hours later than 0 longitude.

Longitude is measured in degrees for determining precise position from east to west, while time is measured based a 24 hour cycle.  360 degrees divided by 24 hours equals earth’s rotational velocity of 15 degrees per hour.  We are 96 degrees west of the Prime Meridian, in the Central US Time Zone 6 hours earlier. Tulsa is just waking when it’s Noon in the UK.

During Earths annual 300,000,000+ mile orbit of the sun, the background of stars appears to shift forward 4 minutes every night. Why? This is because 1,440 minutes in a day divided by the 360 degrees of our orbit around the sun equals 4 minutes. Yes - the earth moves one degree per day relative to the sun.  So while the the earth rotates once every 24 hours, the starry background rotates a little faster - one revolution every 23 hours and 56 minutes.

 Right Ascension - RA keeps track of star time or “siderial” time. Like “solar” or normal time, it is also measured in hours, minutes, and seconds, and likewise shares the Greenwich Meridian as a starting point. A siderial day is four minutes longer than a solar day and represents the true rotational period of the earth relative to any point in space beyond our solar system.

Declination is identical in units of measurement to latitude, the only difference being that latitude pertains to earth’s surface, and Declination pertains to the corresponding place directly overhead in the sky.

Every point in space as seen from earth has a a specific Right Ascension and Declination

We can use Declination and Right Ascension to visit any address in the Universe

For example - The star VEGA in the constellation of LYRA is located at RA 18 hours, 36 minutes, 56.2 seconds; and Declination 38 degrees, 47 minutes, and 01 seconds.  It should be noted that one degree of Declination consists of 60 minutes of arc, each of which consists of 60 seconds of arc. A little quick math lets you know that declination minutes and seconds are much smaller units (1/15) than the minute and second measurements of right Ascension; so to avoid confusion, we do not use the terms “minutes” and “seconds” any more than we have to;  instead, we describe approximate fractions of a degree. The full moon is half of a degree, and the first & third quarter moon is 1/4 degree wide. That gets us close enough to the neighborhood to find most anything.

The “SETTING CIRCLE”, a physical ring mounted on each axis of an equatorial (aligned with the earths polar axis) telescope mount allows one to aim the telescope to a given address in space when the person knows his location and the exact time (based on the Greenwich Meridian’s time).

 Today, conventional setting circles have mostly  given way to digital setting circles (DSC) and “Go To” computers that allow telescopes to be accurately pointed based on digital data libraries.  

Astronomers often choose to count on spatial memory  to revisit their favorite objects using the small finder scopes on their main telescope to center the object.  New technology allows certain telescopes to aim at an object simply by the observer selecting the object designation from a list. For the most part, manual setting circles are hardly ever used anymore.  We wanted you know about them however, for the same reason the Navy wants it’s sailors to know how to use an old fashioned sextant; in the absence of modern conveniences, it is good to know how things were done in the past.  It might come in handy if you are lost in the woods - or at sea - or in space.

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