1:45 PM - 3:15 PM
[O02-P25] Sprite -The Transition of Luminosity, or Energy over Time-
Keywords:sprite, interlace withdrawal, flat plane correction, Pogson's formula, H-R graph, solar constant
Since 2004, our research team has observed and researched it using Watec100N, a high sensitivity monochrome video camera, and UFOCapture, a software which always monitors video data on computer memory, and records two seconds, or one second each before and after the occurrence of some changes when it detects them. Moreover, we introduced two lenses with different focal lengths in 2014. One is an 8mm wide angle lens, and the other is a 25mm telephoto lens. This year, we placed an emphasis on the transition of energy over time. Therefore, we are researching luminosity's transition of energy in the time frame of up to 1/12th of a second in one event.
First of all, we thought that we should compare sprite with the magnitude of other heavenly bodies in the same picture in order to measure the energy of sprite. We identified the magnitude of a heavenly body, using a software which can simulate an observation into outer space at any given moment and at any given place on earth. Therefore, we chose ε Ursa Minor (4.2mag) which has an unsaturated luminosity value.
In contrast to fixed stars which continuously emit light, sprite can be observed in a very short time. We divided one picture taken from a video clip (30fps) into two pictures, each with a set of frames recorded at different times using GIMP, a free software to process images. This process is called Interlace Withdrawal. It enabled us to view the change in sprite’s luminosity in a high resolution of 60fps.
To set the coordinates (1,1) on the top left and (640,480) on the bottom right of all five pictures, we set the horizontal axis as the x-axis and the vertical axis as the y-axis. We also expressed the luminosity as a scale of 256, in other words 0 to 255.
However, lenses have a property which enlarges the luminosity in the images called limb darkening. So, we did a flat plane correction to divide the luminosity value in the images by that of the picture of vignette components which were taken through the same lens. The back ground value is then subtracted from it. Like so, we found the real luminosity value.
We expressed the unit of sprite’s luminosity as mag/sq-deg by substituting the real value for Pogson’s formula. In consequence, most of the sprite’s magnitude is less than that of the Milky Way. Thus proving that sprite is brighter than the Milky Way.
Thanks to the H-R graph which has B-V as its horizontal axis, we found the absolute magnitude of ε Ursa Minor. We also compared the energy of ε Ursa Minor with the energy of sprite in terms of both of their distance ratios, basing it on the solar constant. In conclusion, we were able to successfully find the total amount of energy in one portion of the sprite.