Godlike Productions - Reply to Thread

Users Online Now: 2,091 (Who's On?)	Visitors Today: 1,819,828
Pageviews Today: 2,677,886	Threads Today: 725	Posts Today: 15,144
09:45 PM

REPLY TO THREAD

Subject Moons crescent phase orientation tilts from 2:00 to 4:00 direction in just 2 hours

User Name

Font color: Font:

In accordance with industry accepted best practices we ask that users limit their copy / paste of copyrighted material to the relevant portions of the article you wish to discuss and no more than 50% of the source material, provide a link back to the original article and provide your original comments / criticism in your post with the article.

[quote:The Gentle Astromut:MV8zNjIxMDUyXzY0NjUzNzIzXzY4NkNGNjYx]
[quote:Anonymous Coward 74729691:MV8zNjIxMDUyXzY0NjUzNjI4X0ZFN0M0NURF]
[quote:Hydra:MV8zNjIxMDUyXzY0NjUzNDkwXzEwRDdDMDQ5]
[quote:Anonymous Coward 75461152:MV8zNjIxMDUyXzY0NjUzMTk3Xzg4Nzg5NzAx]
[quote:Hydra:MV8zNjIxMDUyXzY0NjUzMTMyXzJGRDhCMDQ=]
[quote:Anonymous Coward 74336040:MV8zNjIxMDUyX0M1MTY3OEFF]
The lit portion of the moon tilts from 2 oclock when the sun is setting, pointing away from where the suns direction is coming from mind you, to 4 oclock where the sun then sets from our perspectivd after about 2 hours later.

Been seeing this happen consistently for several days now.

Can anybody explain this?
[/quote]
Search term of the day: moon field rotation
[/quote]
[b][color=brown]Thought this only applies to cameras with an az mount, whereas we can just easily turn our heads.[/color][/b]

"Im not saying its field rotation, but its field rotation"
[/quote]
Did you turn your head during your observation in the way an EQ mount would turn?
Or stayed the horizon horizontal during your observation in the way an AZ mount would move?

.
[/quote]

The latter im assuming since i just look at it, im not tilting my head thats for sure.

But labeling a phenomenon doesnt explain it, it just names it. For example, the earth has gravity. Okay but wth is it?
[/quote]

Field rotation is a natural consequence of viewing the Moon from a non-polar aligned perspective. It's demanded by the geometry of the situation and simple math shows that it is quite normal.
[youtube]https://youtu.be/R4eDT8-73ZE[/youtube]
Take the equatorial coordinates and add .25 degrees to declination (approximate radius of the moon). This will give you the equatorial coordinates of both the center point of the moon and the north point of the moon on the equatorial grid. Then calculate the position angle of the moon's bright limb relative to the north equatorial point. This is given by the following equation:

X = arctan((cos(declination of the sun)*Sin(right ascension of the sun - right ascension of the moon))/(cos(declination of the moon)*sin(declination of the sun)-sin(declination of the moon)*cos(declination of the sun)*cos(right ascension of the sun - right ascension of the moon)))

Then to calculate for field rotation, convert the equatorial coordinates of both the center point and the north point to horizon coordinates. This is given by the following formulae. For azimuth, the formula is:
tan(az)=(-sin(Hour angle in degrees +delta)*cos(declination))/(sin(declination)*cos(latitude)-cosnope(declination)*sin(latitude)*cos(hour angle in degrees+delta)) 
where delta is:
tan(delta)=(p*cos(theta')*sin(hour angle in degrees))/((distance of moon in km/6378.14)*cos(declination)-p*cos(theta')*cos(hour angle in degrees))
For altitude the formula is:
sin(altitude)=(sin(declination)*sin(latitude))/(cos(declinatinopeon)*cos(latitude)*cos(hour angle in degrees))
Now once you have converted both the center point and north point to altitude and azimuth, take the difference of each (altitude and azimuth) between the north and center points to find delta alt and delta az. From there, calculate the angle of the line from the center point to north point relative to the horizon:
arctan(delta alt/delta az)
Then add the position angle of the moon. In order to express the resulting orientation angle of the moon relative to the horizon as I have (as an angle expressed as degrees from vertical from 0 to 90 degrees) follow these directions:
angle1 = arctan(delta alt/delta az)
If angle1 > 360, then take angle-360 = angle2, otherwise angle1 = angle2.
If angle2 >90 and less than or equal to 180, then take (90-angle2)+90 = angle3, otherwise angle2 = angle3.
If angle2 = angle3 and angle2 > 180 and less than or equal to 270, then take the absolute value of (180-angle2) = angle4, otherwise angle3 = angle4. 
Finally, if angle4 = angle2 and angle 2 > 270, then take (90-(angle2-180)+90) = angle5, otherwise angle4 = angle5. Angle5 is the final answer and the apparent orientation of the moon relative to the horizon expressed as the angle from 0 to +90 degrees from vertical.
[/quote]

Original Message The lit portion of the moon tilts from 2 oclock when the sun is setting, pointing away from where the suns direction is coming from mind you, to 4 oclock where the sun then sets from our perspectivd after about 2 hours later.

Been seeing this happen consistently for several days now.

Can anybody explain this?

Pictures (click to insert)





\| Next Page >>