This may give a better explanation: declination....
The sun's path in the sky is known as the ecliptic.
The planets and the moon also travel along the ecliptic, sometimes a little above it, sometimes a little below.
The stars do not follow the ecliptic.
The moon moves up and down relative to the ecliptic, crossing it twice every 27 days. The moon can be can be up to 5 degrees above or 5 degrees below the ecliptic, and anywhere in between those points. The moon crosses the ecliptic twice every month, but is more or less 'on the ecliptic' as it doesn't go very far away from it.
Sun and moon both follow the ecliptic, the same ecliptic because there is only one! so it is logical to assume that a full moon would rise twelve hours latter in more or less the same position as the sun had risen that morning.
But the full moon rises in the same place as the sun rises only twice every year (at the equinox).
I personally think that this is interesting enough to build into monuments.
The reason why it doesn't make sense that the midwinter full moon rises in the same position as the midsummer sun rise is simply that we all get so used to explaining how the ecliptic is at its maximum position above or below the equator at the solstices.
We forget that the summer solstice sun at 23.4 degrees above the equator is time specific, it is the position of the sun in relation to the meridian; the solstice sun is at a maximum height above or below the equator at midday.
The angle of the ecliptic (relative to the celestial equator) changes throughout the day.
The angle of the ecliptic, how high or low it is in the sky depends on:
At a certain time every 24 hours* the ecliptic will be 23.4 degrees above the equator, then twelve hours latter it will be 23.4 degrees below it, and the ecliptic rotates almost a full circle every 24 hours.
*As the earth rotates once every 23 hrs and 56 mins (compared to a complete rotation using the sun as a marker) the ecliptic slips backwards (compared to solar time) by 4 minuets. 4 mins = 1 degree change in position
The ecliptic is at its highest point at midday at the summer solstice.
Six hours latter, the highest part of the ecliptic is over in the west.
As the ecliptic rotates, the hour when the moon rises may correspond to a time when the ecliptic is much higher or lower in the sky than the day-time sun had been.
So, to recap:
Every day the ecliptic slowly spins from a maximum high (23.4 degrees) to a maximum low (-23.4 degrees) and back again.
As I write this, right now, the highest part of the ecliptic is in the east.
But, by 7 PM tonight, the ecliptic will be 23.4 degrees above the equator, at its maximum declination.
One month latter, 7th April, the ecliptic will be at its highest point one hour latter.
The rotation of the ecliptic loses one degree westward a day.
There are approximately 90 days between equinox and solstice.
Therefore the ecliptic moves approximately 90 degrees between equator and solstice. It is traditional to measure this as the sun crosses the meridian (midday). The height of the midday sun from the equator is called declination.
The ecliptic moves roughly 90 degrees every six hours.
The dotted line in the diagram is the ecliptic.
A full moon rises as the sun sets.
At midwinter, the full moon rises approximately 4.5 hrs after the sun has crossed the meridian.
At midsummer, the full moon rises approximately 8.5 hrs after the sun has crossed the meridian.
It takes 4 minuits for the ecliptic to move by 1 degree.
The sun's path in the sky is known as the ecliptic.
The planets and the moon also travel along the ecliptic, sometimes a little above it, sometimes a little below.
The stars do not follow the ecliptic.
The moon moves up and down relative to the ecliptic, crossing it twice every 27 days. The moon can be can be up to 5 degrees above or 5 degrees below the ecliptic, and anywhere in between those points. The moon crosses the ecliptic twice every month, but is more or less 'on the ecliptic' as it doesn't go very far away from it.
Sun and moon both follow the ecliptic, the same ecliptic because there is only one! so it is logical to assume that a full moon would rise twelve hours latter in more or less the same position as the sun had risen that morning.
But the full moon rises in the same place as the sun rises only twice every year (at the equinox).
I personally think that this is interesting enough to build into monuments.
The reason why it doesn't make sense that the midwinter full moon rises in the same position as the midsummer sun rise is simply that we all get so used to explaining how the ecliptic is at its maximum position above or below the equator at the solstices.
We forget that the summer solstice sun at 23.4 degrees above the equator is time specific, it is the position of the sun in relation to the meridian; the solstice sun is at a maximum height above or below the equator at midday.
The angle of the ecliptic (relative to the celestial equator) changes throughout the day.
The angle of the ecliptic, how high or low it is in the sky depends on:
- where you are (latitude)
- Where the earth is on its journey around the sun (Earth's latitude) and
- On the time of day (hour angle).
- The elevation angle of the celestial equator = 90 degrees - your latitude. remains constant over the year.
- Earth's latitude = number of days since vernal equinox/ days in the year 365.24 x 360
- Hour angle = 360 x (hour- after midday- /24)
At a certain time every 24 hours* the ecliptic will be 23.4 degrees above the equator, then twelve hours latter it will be 23.4 degrees below it, and the ecliptic rotates almost a full circle every 24 hours.
*As the earth rotates once every 23 hrs and 56 mins (compared to a complete rotation using the sun as a marker) the ecliptic slips backwards (compared to solar time) by 4 minuets. 4 mins = 1 degree change in position
 |
| The angle of the equator. |
Six hours latter, the highest part of the ecliptic is over in the west.
As the ecliptic rotates, the hour when the moon rises may correspond to a time when the ecliptic is much higher or lower in the sky than the day-time sun had been.
So, to recap:
Every day the ecliptic slowly spins from a maximum high (23.4 degrees) to a maximum low (-23.4 degrees) and back again.
As I write this, right now, the highest part of the ecliptic is in the east.
But, by 7 PM tonight, the ecliptic will be 23.4 degrees above the equator, at its maximum declination.
One month latter, 7th April, the ecliptic will be at its highest point one hour latter.
The rotation of the ecliptic loses one degree westward a day.
There are approximately 90 days between equinox and solstice.
Therefore the ecliptic moves approximately 90 degrees between equator and solstice. It is traditional to measure this as the sun crosses the meridian (midday). The height of the midday sun from the equator is called declination.
The ecliptic moves roughly 90 degrees every six hours.
The dotted line in the diagram is the ecliptic.
A full moon rises as the sun sets.
At midwinter, the full moon rises approximately 4.5 hrs after the sun has crossed the meridian.
At midsummer, the full moon rises approximately 8.5 hrs after the sun has crossed the meridian.
It takes 4 minuits for the ecliptic to move by 1 degree.
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