by MarkBour » Wed Aug 12, 2020 5:42 pm
I think it would be important for this exercise to take the images of the comet at the exact same time, local time each night. Then using the approximation of drawing the lines (rays, actually) as a reverse extension of the ion tail. I don't know how well the ion tail approximates the anti-solar direction, perhaps it is near enough perfect for this purpose. It would be my first inclination (sorry for that pun) to extend the rays until they intersected and say "that's where the Sun is." But as @Chris Peterson and the APOD caption point out, the Sun's apparent position at a given time of day shifts along the ecliptic, so there is no single point of intersection (though it might look like there is for a short period of days).
But what has this APOD done? It has taken a region on the surface of the earth (somewhat consistent in altitude) and inscribed the point of intersection of these rays with the ground. Will this draw out a version of the analemma? To the extent that the ion tail is giving a precise direction pointer to the Sun and that the comet can act as a proxy for an observer on the Earth, this should work. It's a cleverly-noticed indicator of the direction to the Sun at a time of day when the Sun is below the observer's feet. However, the comet is a point way off the Earth and it also moved across the sky during this time. Therefore, I believe the figure these points would eventually draw out would be some perverted version of the standard analemma.
Also, thanks, @Sa Ji Tario, I had to look up "alidades" to learn what those were.
I think it would be important for this exercise to take the images of the comet at the exact same time, local time each night. Then using the approximation of drawing the lines (rays, actually) as a reverse extension of the ion tail. I don't know how well the ion tail approximates the anti-solar direction, perhaps it is near enough perfect for this purpose. It would be my first inclination (sorry for that pun) to extend the rays until they intersected and say "that's where the Sun is." But as @Chris Peterson and the APOD caption point out, the Sun's apparent position at a given time of day shifts along the ecliptic, so there is no single point of intersection (though it might look like there is for a short period of days).
But what has this APOD done? It has taken a region on the surface of the earth (somewhat consistent in altitude) and inscribed the point of intersection of these rays with the ground. Will this draw out a version of the analemma? To the extent that the ion tail is giving a precise direction pointer to the Sun and that the comet can act as a proxy for an observer on the Earth, this should work. It's a cleverly-noticed indicator of the direction to the Sun at a time of day when the Sun is below the observer's feet. However, the comet is a point way off the Earth and it also moved across the sky during this time. Therefore, I believe the figure these points would eventually draw out would be some perverted version of the standard analemma.
Also, thanks, @Sa Ji Tario, I had to look up "alidades" to learn what those were.