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Astronomy/an angular distance question

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Expert: - 9/8/2009


Question
Hi Mr. Whiting!

I was wondering if you knew how to calculate the angular distance from horizon to horizon that the sky takes up? When I tried to find an answer I found 100, 180, 360, 90, and dependent on altitude. Which one is it?

Thanks so much,
Jaiden

Answer
Hi Jaiden,
At sea level, it's 180 degrees.  It is 90 degrees from say the western horizon up to the zenith (point directly overhead), and another 90 degrees down to the eastern horizon, for a total of 180 degrees.
And it doesn't matter which compass direction you use, as long as you maintain a straight arc
through the zenith.
(90 degrees forms a right angle, like the corner of a piece of 8.5 x 11 sheet of paper, and
there are 360 degrees in a complete circle;  180 degrees also represents a straight line,
like in this example, horizon to horizon.)  
Clear Skies,
Tom Whiting
Erie, PA USA

Other easy examples of an angular measurement are:
45 degrees is halfway up the sky from the horizon to the zenith. (half of 90 degrees).
The full moon disk measures 1/2 degree and so does the sun's disk.
A fistwidth held out at arm's length represents about a 5 degree angle.
A fully extended handspan at arm's length represents about 15 degrees of sky,
and is the amount the Earth rotates eastward (or sky westward) in one hour.
15 degrees per hour times 24 hours equals 360 degrees, or a full circle.
Tom

Astronomy

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Tom Whiting

Expertise

Astronomy has been my hobby/pasttime for over 50 years.  Currently own 3 telescopes, the largest of which is a 30 inch Newtonian truss Dob that is portable.I taught Astronomy/Meteorology at the University Level for 13 years before retiring in 1995. Being retired and home most of the time, I am able to answer all questions relatively quickly, unless it's a new moon weekend with good observing conditions.  No astrology questions please, or questions about alleged UFO picture identifications.

Experience

Experience: Astronomy has been my hobby and study for over 50 years. We currently now own a 30 inch portable telescope (Updated - Pennsylvania`s largest portable telescope). It can be seen on our website at:http://www.velocity.net/~bwhiting and also attend several regional starparties during the year, and have been on 5 total solar eclipse expeditions.

Organizations: President, Erie County Mobile Observers Group for over 15 years.

Publications: Wrote the "Over Erie Skies" newspaper article in our local newspaper for 11 years (1975-86).

Education: Masters Degree- Taught at the University level for 13 years. Retired 20 years -USAF Pilot - KC-135 with 180 combat missions;  Also Eagle Scout, Philmont staff 2 Yrs, Order of Arrow Lodge Chief, Ham Radio (inactive).

Awards: two discoveries: The mini-coathanger asterism in Ursa Minor (the little dipper) And the mini-ladle- another asterism in the bowl of Ursa Minor. Clients: Currently President of the ECMOG as mentioned above.

Education/Credentials
BS  Metallurgical Engineering Grove City College, PAMaster's Degree, Gannon University, Erie, PA Also retired USAF pilot, 20 years.

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