First, direction.
A compass needle points to magnetic north.
Magnetic north is not true north.
It tends to wander, and isn't at the Pole at all!
The earth spins 360 degrees every 'day'.
The axis of spin -like a pole pushed through the earth extending into space, and the earth spins around this pole- is imagined as a north - south line running through the center of the earth.
The meridian is an imaginary line connecting north to south running over the surface of the earth.
The celestial meridian connects north and south, overhead, through the zenith...
The equator is at right angles to the meridian (runs east - west).
The azimuth is the compass alignment expressed in degrees.
So the midsummer sun rises here in a north-east direction, around 50 degrees azimuth.
1/ North is 0 degrees azimuth.
2/ East is 90 degrees azimuth.
3/ South is 180 degrees azimuth.
4/ West is 270 degrees azimuth.
Latitude is the angle from the ground, upwards to the still point in the sky (the pole)
In our time the star marking this position is Polaris.
1 degree of latitude is roughly 70 miles.
At the equator, the pole star remains stationary on the horizon.
At the North pole, the pole star remains stationary directly over head (at the zenith).
When measuring azimuth...
If using a compass - take account of magnetic declination : http://www.ngdc.noaa.gov/geomag-web/#declination
A rough measurement of the sun's azimuth and elevation angle can be found by shadows; good for azimuth, but not so accurate for elevation angle.
Any possible alignments between, stones or entrance or exits of a monument with the sun and moon is best determined by visiting the monument and being there to see it happen. Photographs of the site are essential for desktop research.
Solstice and equinox.
The tilt of the earth (axial tilt) in relation to the sun means that sun rise appears to move between two extremes at the solstices each year.
The moon.
It takes an average of about 29 days for the moon to go from full, through new and back to full.
This is the time it takes to circle the earth once ( a month is one moon year).
What we see of the Moon, how much of the moon sunlight reflects from changes because the moons angle to the sun changes. When the moon is 'close' to the sun, we see a crescent. When the moon is opposite the sun, we see a full moon.
Remember a midsummer full moon rises in a midwinter sun rise position. And the midwinter full moon will rise in the midsummer sun's rise position with an extra + or - due to the angle of the moon in relation to the ecliptic. Therfore, the winter solstice full moon at Stonehenge will rise close to or even over the Heel stone- so the Heel stone isn't necessarily a helios stone at all.
Elevation angle of celestial equator looking south:
90 degrees - latitude.
90 - 51 = 39 degrees.
At Stonehenge, the sun at midday at the equinox will have an elevation angle of 39 degrees, as measured from the ground up.
Declination.
Over the year the sun rises higher than the equator, reaching a maximum height above the equator of angle of celestial equator + angle of ecliptic:
Summer solstice.
39 + 23.5 = 62.5
Winter solstice.
The sun sinks below the equator.
Equator angle - angle of the ecliptic = solstice elevation angle
39 - 23.5 = 15.5
Next...
A compass needle points to magnetic north.
Magnetic north is not true north.
It tends to wander, and isn't at the Pole at all!
The earth spins 360 degrees every 'day'.
The axis of spin -like a pole pushed through the earth extending into space, and the earth spins around this pole- is imagined as a north - south line running through the center of the earth.
The meridian is an imaginary line connecting north to south running over the surface of the earth.
The celestial meridian connects north and south, overhead, through the zenith...
The equator is at right angles to the meridian (runs east - west).
The azimuth is the compass alignment expressed in degrees.
So the midsummer sun rises here in a north-east direction, around 50 degrees azimuth.
1/ North is 0 degrees azimuth.
2/ East is 90 degrees azimuth.
3/ South is 180 degrees azimuth.
4/ West is 270 degrees azimuth.
Latitude is the angle from the ground, upwards to the still point in the sky (the pole)
In our time the star marking this position is Polaris.
1 degree of latitude is roughly 70 miles.
- Latitude at the equator is zero.
- Latitude at the poles is 90 degrees.
- The equator is 90 degrees to the meridian.
At the equator, the pole star remains stationary on the horizon.
At the North pole, the pole star remains stationary directly over head (at the zenith).
When measuring azimuth...
If using a compass - take account of magnetic declination : http://www.ngdc.noaa.gov/geomag-web/#declination
A rough measurement of the sun's azimuth and elevation angle can be found by shadows; good for azimuth, but not so accurate for elevation angle.
Any possible alignments between, stones or entrance or exits of a monument with the sun and moon is best determined by visiting the monument and being there to see it happen. Photographs of the site are essential for desktop research.
Solstice and equinox.
The tilt of the earth (axial tilt) in relation to the sun means that sun rise appears to move between two extremes at the solstices each year.
- Summer solstice- midsummer- 21st June. Sun rises north east
- Winter solstice- midwinter- 21st December. Sun rises south east.
- Spring equinox- 21st March. Sun rise east.
- Autumn equinox- 21st September. Sun rise east.
It takes an average of about 29 days for the moon to go from full, through new and back to full.
This is the time it takes to circle the earth once ( a month is one moon year).
What we see of the Moon, how much of the moon sunlight reflects from changes because the moons angle to the sun changes. When the moon is 'close' to the sun, we see a crescent. When the moon is opposite the sun, we see a full moon.
Remember a midsummer full moon rises in a midwinter sun rise position. And the midwinter full moon will rise in the midsummer sun's rise position with an extra + or - due to the angle of the moon in relation to the ecliptic. Therfore, the winter solstice full moon at Stonehenge will rise close to or even over the Heel stone- so the Heel stone isn't necessarily a helios stone at all.
- Every month the Moon changes from a crescent, to full then back to crescent.
- From January to July the full moon rise is southbound until it goes just beyond the south east.
- From July to January the full moon rise is northbound, going just a little beyond north east.
- From January until June the sun rise is north bound until it reaches north-east at midsummer.
- From July to December the sun travels south until it reaches south-east at midwinter.
Elevation angle of celestial equator looking south:
90 degrees - latitude.
90 - 51 = 39 degrees.
At Stonehenge, the sun at midday at the equinox will have an elevation angle of 39 degrees, as measured from the ground up.
Declination.
Summer solstice.
39 + 23.5 = 62.5
Winter solstice.
The sun sinks below the equator.
Equator angle - angle of the ecliptic = solstice elevation angle
39 - 23.5 = 15.5
Next...
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