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Guest, Join Papa Zoom today for some uplifting biblical encouragement! --> Daily Verses
Where Has The Summer Gone?
- Thread starter HeIsRisen2018
- Start date
I personally like a bit of winter. The only thing is that around February (my birthday month) I start getting sick of it. It sure is nice to have white Christmases though.
jasonc
Member
Mild,105 with no shade isn't mild.humidity kills,desert weather ain't crap.been to the stan,130 by 8 am.still pales to florida
A huge grin stretched a crossed my face when I saw good old Papa Zoom's face come up. Good old Dan, it sure looks like he's having fun.
We love you Papa! 
(I loved the music too it was sort of like Christian/Celtic music)
tim-from-pa
Member
Exactly-- running out of summer. As for sundials, I think you mean right ascension (meridian) rather than azimuth if we are discussing any dial with a gnomon parallel to the axis of the earth. However, some sundials utilize the sun's declination. One example is a gnomon that corrects for the equation of time that then projects onto the sundial face or ring. The equation of time is very much dependent on solar declination. Another example is a sundial that utilizes a vertical gnomon such as an analemmatic sundial.
King Dan of Great the 1st
Member
It will be summer soon.
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It is my understanding that the sun only tracks right ascension at the equator. North of the equator, its apparent motion describes an arc part way between right ascension and the horizon. Go far enough north and the sun doesn't set at all during the summer. It just describes a slow arc around the horizon. Azimuth would be the correct technical term for non equatorial arcs, although right ascension gives the general idea in most latitudes.
Maybe I got it all mixed up though. Wouldn't be the first time.
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tim-from-pa
Member
Yeah it has to do with spherical trigonometry. Basically, the line of right ascension is the longitude the sun is at right at the moment of the vernal equinox -- this point becomes zero hours. You can imagine it as putting a flash bulb in the middle of the earth and at that point in time it goes off and projects the latitude and longitude lines into space. Latitude now become declination and longitude, right ascension. The stars do not change their right ascension in a day and the sun more or less is the same throughout the day with our orbit causing very little shift. However, we rotate and different lines of longitude face the sun each hour (meridians). This is what a common sundial gnomon measures the angular distance about the pole and the meridian (related to hours since we rotate about 15 degrees per hour). In this case, declination does not matter. When the sun's declination changes throughout the year, you can imagine the same hour as "sliding up or down" relative to the gnomon axis, which is also the earth's axis. This is how the sun can have a different altitude and azimuth various times of the year and yet the pole angle (meridian) is the same and measures the same time.
Now, that said, Altitude and Azimuth is usually angular measure at a person's locality. Altitude is the angular distance above the horizon, meaning the highest point (the zenith) is 90 degrees. Azimuth is the angular distance around the horizon toward something. It is usually measured from the north meaning north is zero, east is 90, south is 180 and west is 270 degrees. This is also deemed bearing along a route or colloquially, it's "direction". When I pray, I like to face Jerusalem which has an Azimuth of about 53 degrees (somewhat northeast direction) from my location near Philadelphia Pa. This is the true and most direct distance, aka "great circle arc" on a globe. So that is an example of azimuth. A star over Jerusalem Israel would appear here as a low star in the Northeast, so again, the elevation of the star is its altitude, and the direction the azimuth. It is not the same for everyone depending where one lives, but the declination and right ascension is the same all over the globe.
Hope everyone enjoyed tonight's math lecture about the mathematics of summer.
https://en.wikipedia.org/wiki/Right_ascension
Celestial mechanics boggles my brain. Anyway, I think I understand what you mean. Tracking the sun's apparent path across the sky lets you closely approximate what right ascension is at the equator, adjusted for change in declination as seasons move away from the vernal equinox.
However technically... On this Wiki map of the celestial sphere, right ascension is lined up with apparent motion of the sun only at the equator. Only on the vernal equinox. (I'm not sure why it wouldn't line up on the Autumnal equinox.) That is, you can only directly measure right ascension at the equator during the vernal equinox. Nowhere else. From the Wiki article you posted:
Measured along the "celestial equator". Check out the celestial sphere gif. Celestial equator lines up with the earth's equator. If it was measured by apparent motion of the sun north of the equator, it would gradually flip 90 degrees by the time it reached the north pole. Near the north pole, the sun doesn't rise and set in the summer. It just moves slowly around the horizon. In the winter its just gone. There is nothing to measure.
Additionally, people north of the equator are standing at an angle compared to how people are aligned with the earth at the equator. Gravity tends to accelerate people toward a common earth/person centroid. Okay so technically gravitons act by warping the space time continuum, not simply attracting, but that is another thread.
To correctly point in the direction of earth's rotation north of the equator, you have to tilt your body at an angle before pointing east. Pointing east while standing straight up would not describe a line parallel to the equator. Gravity gradually tilts people 90 degrees from the angle they are standing at the equator. Someone standing at the north pole would be pointing at a curved line that goes from the north pole to the south pole and back if he held his arm out straight. At the equator a person holding his arm out straight and pointing east would be pointing in the direction of a curved line following the circumference of the earth along the equator.
So tracking the sun from east to west would be tracking the sun's azimuth from 90 to 270 degrees, adding in the changing altitude vector? In PA the sun rises in the east, tracks across the southern sky, and then sets in the west. Tracking azimuth from 90 to 270 would let you know what right ascension is at the equator (which longitude the sun is at there?) Although this may only be the case at the vernal equinox. There is probably some mathematical adjust to correct for variations in declination as seasons move away from the vernal equinox though.
Anyway, it was a fun discussion. I enjoyed it, and your lecture.
However technically... On this Wiki map of the celestial sphere, right ascension is lined up with apparent motion of the sun only at the equator. Only on the vernal equinox. (I'm not sure why it wouldn't line up on the Autumnal equinox.) That is, you can only directly measure right ascension at the equator during the vernal equinox. Nowhere else. From the Wiki article you posted:
Wiki said:
Measured along the "celestial equator". Check out the celestial sphere gif. Celestial equator lines up with the earth's equator. If it was measured by apparent motion of the sun north of the equator, it would gradually flip 90 degrees by the time it reached the north pole. Near the north pole, the sun doesn't rise and set in the summer. It just moves slowly around the horizon. In the winter its just gone. There is nothing to measure.
Additionally, people north of the equator are standing at an angle compared to how people are aligned with the earth at the equator. Gravity tends to accelerate people toward a common earth/person centroid. Okay so technically gravitons act by warping the space time continuum, not simply attracting, but that is another thread.
To correctly point in the direction of earth's rotation north of the equator, you have to tilt your body at an angle before pointing east. Pointing east while standing straight up would not describe a line parallel to the equator. Gravity gradually tilts people 90 degrees from the angle they are standing at the equator. Someone standing at the north pole would be pointing at a curved line that goes from the north pole to the south pole and back if he held his arm out straight. At the equator a person holding his arm out straight and pointing east would be pointing in the direction of a curved line following the circumference of the earth along the equator.
So tracking the sun from east to west would be tracking the sun's azimuth from 90 to 270 degrees, adding in the changing altitude vector? In PA the sun rises in the east, tracks across the southern sky, and then sets in the west. Tracking azimuth from 90 to 270 would let you know what right ascension is at the equator (which longitude the sun is at there?) Although this may only be the case at the vernal equinox. There is probably some mathematical adjust to correct for variations in declination as seasons move away from the vernal equinox though.
Anyway, it was a fun discussion. I enjoyed it, and your lecture.
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More boggling of my tiny brain. Jerusalem would seem to be somewhat southeast of PA on this map. Philadelphia's latitude is 39.9526° N, and Jerusalem's is 31.7683° N.
Movable Type Scripts said:
Did you use a forward azimuth (initial bearing) calculator to arrive at your number? Jerusalem is closer to the equator than Philadelphia is. It gets more sunlight, and is warmer. I think the way it works is that forward azimuth calculators will send you on a curved path that starts northward, and then slopes southward further along the journey.
You can test this theory by running the calculator backward. Put Jerusalem's coordinates in first, and use Philadelphia as your destination. If it is a forward azimuth calculator, the direction will still read north. They can't both be north of each other. That is just the initial bearing, which will change further in the journey.
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