Some spring equinox notes for Utah science teachers
The following are some notes on tomorrow's spring equinox that may be of use to Utah educators. The spring equinox is tomorrow, 3/20/2006 at 18:26 UTC (11:26 MDT). The NASA/JPL Horizons Ephemeris << http://ssd.jpl.nasa.gov/?ephemerides >> for my topocentric observing point (o.p.) ( 111°53'27.6''W, 40°45'23.0''N ), shows Sun crossing 0 deg ecliptic longitude between 18:25 and 18:26 UT: Date/Time Az/Alt Eclip Long Lat Local solar time 2006-Mar-20 18:25 154.2263 46.2549 359.9995381 -0.0018950 10 49 00.7171 2006-Mar-20 18:26 154.5682 46.3370 000.0002209 -0.0018920 10 50 00.7313 Local transit of the Sun (our topocentric equinox) occurs later at 19:34-19:35 UT (12:34-12:35 pm MDT): Date/Time Az/Alt Eclip Long Lat Local solar time 2006-Mar-20 19:34 179.6279 49.2600 0.0466343 -0.0016771 11 59 01.7169 2006-Mar-20 19:35 180.0111 49.2608 0.0473167 -0.0016739 12 00 01.7312 2006-Mar-20 19:36t 180.3942 49.2604 0.0479991 -0.0016706 12 01 01.7456 At this point, that this observing point's latitude (~ 41N degs) is equal to 90 degrees (zenith) minus the altitude of the Sun, e.g. - 41 degs = 90 degs - 49 degs Due to the effect of precession, from this SLC topocentric o.p., the Sun does not cross the celestial coordinate spring equinox until 20:22-20:23 UT (1:22-1:23pm): Date/Time RA/Dec Alt/Az 2006-Mar-20 20:22 23 59 59.85 -00 00 07.1 197.6971 47.8966 2006-Mar-20 20:23 00 00 00.00 -00 00 06.1 198.0597 47.8387 These angles can be demonstrated to students using a protractor with a string and hanging weight (like a bolt or nut) run through the center hole - at the 19:34-19:35 UT (12:34-12:35 pm MDT) time mark. The protractor is held so that the string hangs through the 90 degree mark. Then stick a pencil perpendicular to the protractor into the center hole. A fuzzy shadow will be cast by the Sun. To reduce the chance of eye injury, advise students to not sight along the protractor at the Sun. Measure angles indirectly using the pencil's shadow. An accurately aligned north-south building edge (check with a compass) can also be used. Use the protractor to make a large graduated quarter circle on a piece of paper. Using the protractor with plumb bob, tape the graduated circle to the north-south side of the building. Hold a pencil perpendicular to the building and take a shadow measurement. Degree of accuracy for such methods is ~ 1.0 - 3.0 degrees. - Canopus56 __________________________________________________ Do You Yahoo!? Tired of spam? Yahoo! Mail has the best spam protection around http://mail.yahoo.com
--- Canopus56 <canopus56@yahoo.com> wrote: <snip> Some other tips for spring equinox science demonstrations: At the equinoxes, the Sun rises and sets at azimuth 90 degrees (due East) and 270 degrees ( due West). Using an accurately aligned east-west edge of a building, or two stakes driven in the ground, that the sun sets at due west can be illustrated. Your magnetic declination ( the degrees you subtract or add to a compass heading to find the geographic direction, can be estimated from magnetic declination maps at this web site << http://disitron.com/freeresources/ >> ) Another demonstration that can be done on the equinox uses a gnomon, a single stick driven in the ground. Or you can use any existing feature, like a basketball backboard, a street lamp or a flag pole. The equinoxes are the only day of the year that the shadow cast by a gnomon moves in a straight east-west line. Have students go out at one or two hour intervals and mark the location of the shadow of the top of the gnomon on the ground with chalk. The line traced by the shadow will be a straight east-west line. If repeated in few weeks, the line traced by the gnomon's shadow will be curved. - Canopus56(Kurt) __________________________________________________ Do You Yahoo!? Tired of spam? Yahoo! Mail has the best spam protection around http://mail.yahoo.com
What?!? No mention of balancing of eggs on the equinox? :) Actually I'm scheduled to join several people from channel 13 on their 11:30 am newscast tomorrow to try balancing eggs. Ought to be fun. Hopefully I'll also have time to talk about the real facts of equinox. Patrick Canopus56 wrote:
Some other tips for spring equinox science demonstrations:
At the equinoxes, the Sun rises and sets at azimuth 90 degrees (due East) and 270 degrees ( due West). Using an accurately aligned east-west edge of a building, or two stakes driven in the ground, that the sun sets at due west can be illustrated.
Your magnetic declination ( the degrees you subtract or add to a compass heading to find the geographic direction, can be estimated from magnetic declination maps at this web site << http://disitron.com/freeresources/ >> )
Another demonstration that can be done on the equinox uses a gnomon, a single stick driven in the ground. Or you can use any existing feature, like a basketball backboard, a street lamp or a flag pole.
The equinoxes are the only day of the year that the shadow cast by a gnomon moves in a straight east-west line. Have students go out at one or two hour intervals and mark the location of the shadow of the top of the gnomon on the ground with chalk. The line traced by the shadow will be a straight east-west line. If repeated in few weeks, the line traced by the gnomon's shadow will be curved.
- Canopus56(Kurt)
I'll probably walk over to the Gallivan Center at around _12:30pm_ to watch the Gallivan sundial tick off local equinox. I have a couple of large (8") paper astrolables - if you want to borrow 'em. They can used to show the public how the common solar pocket watch worked - in use from 400 C.E. to about the 1820s.
What?!? No mention of balancing of eggs on the equinox? :)
Do eggs balance better in the rain? -:) --- Patrick Wiggins <paw@wirelessbeehive.com> wrote:
What?!? No mention of balancing of eggs on the equinox? :)
Actually I'm scheduled to join several people from channel 13 on their 11:30 am newscast tomorrow to try balancing eggs. Ought to be fun.
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--- Canopus56 <canopus56@yahoo.com> wrote:
I'll probably walk over to the Gallivan Center at around _12:30pm_ to watch the Gallivan sundial tick off local equinox. <snip>
As a continuation of my winter solstice look at the Gallivan Center Sundial, I went over before 12:30pm to see the vernal equinox local noon at the dial. My main interest was in establishing for future reference where on the dial plate, the horizontal traveling line of the gnomon's equinox shadow falls. The overcast clouds did not clear till around 1:00pm sufficient to give a useable view of the dial's light gnomon. The dial plate consists of about five components. The key one here is an inner circular ring which is surrounded by a band containing the symbols of the Greek zodiac. At the equinoxes, the top of the light gnomon moves in a line approximately perpendicular to the gnomon and tangent to the inner or "bottom" side of the zodiac symbol band. - Canopus56 (Kurt) __________________________________________________ Do You Yahoo!? Tired of spam? Yahoo! Mail has the best spam protection around http://mail.yahoo.com
Aloha Any photos of the Gallivan sundial on line?? or in anyones files that can be sent to me?? We talking about using a sundial at the ATST visitor center and I would appreciate seeing what has been done in SLC as a point of reference. Mahalo and Aloha Rob
--- Rob Ratkowski Photography <ratkwski@hawaii.rr.com> wrote:
Aloha Any photos of the Gallivan sundial on line?? or in anyones files that can be sent to me?? We talking about using a sundial at the ATST visitor center and I would appreciate seeing what has been done in SLC as a point of reference.
I don't see one at the Gallivan website: http://www.ci.slc.ut.us/PublicServices/Gallivan/default.htm - Canopus56 (Kurt) P.S. - I haven't forgotten our conversations from December, Rob. I've been working on an observational planner since then and haven't written up some sundial suggestions. __________________________________________________ Do You Yahoo!? Tired of spam? Yahoo! Mail has the best spam protection around http://mail.yahoo.com
Cute article in this month's Night Sky magazine on balancing eggs on the equinox. It tells the history and origin as well as how to actually accomplish this feat (and of course not just on the equinox). You many want to read it Patrick so you are well prepared with answers. Do you know the origin of the story? -A
Here is the egg story in Night Sky: http://reference.aol.com/space/nightsky?id=20060302190209990001 -A
--- Patrick Wiggins <paw@wirelessbeehive.com> wrote:
What?!? No mention of balancing of eggs on the equinox? :)
I'd be interested in hearing about the physics of it in terms of strength of Sun's gravitational field. While the Sun exerts enough gravitational attraction to pull the Earth's oceans "up" many feet, I'm assuming the field strength is too low to affect an egg. - Canopus56 (Kurt) __________________________________________________ Do You Yahoo!? Tired of spam? Yahoo! Mail has the best spam protection around http://mail.yahoo.com
Gravitational gradient would be, basically, nonexistent in an egg. On Mar 20, 2006, at 11:30 AM, Canopus56 wrote:
--- Patrick Wiggins <paw@wirelessbeehive.com> wrote:
What?!? No mention of balancing of eggs on the equinox? :)
I'd be interested in hearing about the physics of it in terms of strength of Sun's gravitational field. While the Sun exerts enough gravitational attraction to pull the Earth's oceans "up" many feet, I'm assuming the field strength is too low to affect an egg.
- Canopus56 (Kurt)
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--- Dave Gary <Dave.Gary@m.cc.utah.edu> wrote:
Gravitational gradient would be, basically, nonexistent in an egg.
That's my point. And the numbers are - in terms of G? - Canopus56 (Kurt)
On Mar 20, 2006, at 11:30 AM, Canopus56 wrote:
--- Patrick Wiggins <paw@wirelessbeehive.com> wrote:
What?!? No mention of balancing of eggs on the equinox? :)
I'd be interested in hearing about the physics of it in terms of strength of Sun's gravitational field. While the Sun exerts enough gravitational attraction to pull the Earth's oceans "up" many feet, I'm assuming the field strength is too low to affect an egg.
- Canopus56 (Kurt)
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--- Canopus56 <canopus56@yahoo.com> wrote: <snip>
Some other ideas for spring equinox science demonstrations:
In Utah, where the streets are grid aligned to the compass points, on the equinoxes you should be able to walk out into a protected portion of a street and watch the sunset aligned with most east-west running streets. Civil sunset tonight is at 6:40pm. For example, outside where I work on 300 South in SLC, there is protected cross-walk and double median. On many occassions over the years, as I have left to go home driving east on 300 South on and a couple of days after the date of the equinoxes, the Sun sets directly "up" 300 South between the tall buildings and illuminates the microwave tower mountain just to the north of Emigration Canyon. At this time of year, the Red Butte (the south side of Red Butte Canyon) also can light up from the setting Sun. Again, all this is cloud limited today. - Canopus56 (Kurt) __________________________________________________ Do You Yahoo!? Tired of spam? Yahoo! Mail has the best spam protection around http://mail.yahoo.com
--- Canopus56 <canopus56@yahoo.com> wrote: <snip> --- Norm Hansen <***> wrote offline:
Hi Kurt, I've been waiting for someone to challenge the premise you state below; I do not see how that can be, except on the equator. At our northern latitude the shadow of the top of the pole would fall directly on the east-west line that passes through the base of the pole at sunrise and sunset (if you have a true horizon visible) but all the rest of the day the shadow would move north of that line, to well over 40 degrees at high noon.
Where am I going wrong in my thinking?
the pole would fall directly on the east-west line that passes through the base
Perhaps I mistated unclearly in my original post. The straight east-west line cast by the shadow of a gnomon on the equinox does not pass through the base, it passes north of the base, as do all shadows cast by gnomons north of the Tropic of Cancer. But the shadow is a straight line. It's counter-intitutive because we are conditioned to think about terresterial reality in terms of the physical parallax created by the distance between human eyes. That parallax is good to about the length of a football field. At 149.6Ã106 km distance, the Sun has a parallax of above 25", I believe, assuming that you stand on opposite ends of the Earth at the same time. This is below the ability of the human eye to detect. Because the light from the Sun is effectively parallel and is aligned with the Earth and celestial equator on the equinoxes - and this is true at all latitudes, all Earth-based gnomons cast a straight east-west shadow on those dates regardless of latitude. Otherwise the shadows are curved. See illustration at - http://www.scottdesignsundials.com/How_to_read/a_Graphic1.gif in - http://www.scottdesignsundials.com/How_to_read/body_how_to_read.htm and informal demo at 16 degree north latitude at website - http://www.sundial.thai-isan-lao.com/equinox_path.html The Pueblo Bonito Ruins in Chaco Canyon, New Mexico, are aligned along a similar east-west line that marks the equinoxes. http://earthobservatory.nasa.gov/Newsroom/NewImages/images.php3?img_id=16974 I would recommend downloading a crippleware program called "Shadows", that allows to you to rapidly design sundial plates for various latitudes, to experiment further. The "Shadows" program also allows you to view, the sundial that you design, an animation of the Sun travesing the sky and the resulting shadow cast by the dial. By my own informal test, yesterday at sundown, the Sun did set right down the middle of 300 South, an East-West running street in SLC. - Canopus56 (Kurt) P.S. Some more info - The ancient Greeks divided the world, in part, into three latitudinal bands based on the shadow cast by straight gnomons. (The triangular gnomon sundial was invented later by the Romans.) The word "Tropic" as in - Tropic of Cancer, at 23° 26' 22" N Tropic of Capricorn, at 23° 26' 22" S - means "to turn" in Latin, from the Greek trop, a turning. For all gnomons north the Tropic of Cancer, all shadows cast by the gnomon throughout the year fall north of the gnomon base. For all gnomons south the Tropic of Cancer and north of the Tropic of Capricorn, shadows cast by the gnomon throughout the year fall both north and south of the gnomon's base. For all gnomons south the Tropic of Capricorn, shadows cast by the gnomon throughout the year always fall south of the gnomon's base. The word "turn" in Tropic of Cancer and Tropic of Capricorn meant to the ancient greeks that the shadows of gnomons marked at noon each day would reverse direction at the solistices start going the other direction (towards or away from the gnomon's base). Because of 2500 years of precession, the shadows no longer turn when the Sun is in those constellations. By convention, we still use those terms on world maps and globes. Other good background on sundials can be found at: The Sundial Primer (website) by Carl Sabanski http://www.mysundial.ca/tsp/tsp.html __________________________________________________ Do You Yahoo!? Tired of spam? Yahoo! Mail has the best spam protection around http://mail.yahoo.com
--- Canopus56 <canopus56@yahoo.com> wrote: P.P.S. - The "Shadows" program can be found at: http://perso.wanadoo.fr/blateyron/sundials/shadowspro/gb/
--- Canopus56 <canopus56@yahoo.com> wrote: <snip> I would recommend downloading a crippleware program called "Shadows", that allows to you to rapidly design sundial plates for various latitudes, to experiment further. The "Shadows" program also allows you to view, the sundial that you design, an animation of the Sun travesing the sky and the resulting shadow cast by the dial.
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--- Canopus56 <canopus56@yahoo.com> wrote: <snip> In rereading my original post, it would have been clearer to explain that the shadow always runs to the north of the gnomon and not across the gnomon's base, as Norm pointed out. - Canopus56(Kurt)
The equinoxes are the only day of the year that the shadow cast by a gnomon moves in a straight east-west line. Have students go out at one or two hour intervals and mark the location of the shadow of the top of the gnomon on the ground with chalk. The line traced by the shadow will be a straight east-west line. If repeated in few weeks, the line traced by the gnomon's shadow will be curved.
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participants (5)
-
Ann House -
Canopus56 -
Dave Gary -
Patrick Wiggins -
Rob Ratkowski Photography