How fast is lightning? Lightning, in fact, moves not only too fast for humans to see, but so fast that humans can’t even tell which direction it is moving. The above lightning stroke did not move too fast, however, for this extremely high time resolution video to resolve. Tracking at an incredible 7,207 frames per second, actual time can be seen progressing at the video bottom. The above lightning bolt starts with many simultaneously creating ionized channels branching out from an negatively charged pool of electrons and ions that has somehow been created by drafts and collisions in a rain cloud. About 0.015 seconds after appearing — which takes about 3 seconds in the above time-lapse video — one of the meandering charge leaders makes contact with a suddenly appearing positive spike moving up from the ground and an ionized channel of air is created that instantly acts like a wire. Immediately afterwards, this hot channel pulses with a tremendous amount of charges shooting back and forth between the cloud and the ground, creating a dangerous explosion that is later heard as thunder. Much remains unknown about lightning, however, including details of the mechanism that separates charges.(via Astronomy Picture of the Day)
A mere 2.5 million light-years away, the Andromeda Galaxy really is just next door as large galaxies go. So close, and spanning some 260,000 light-years, it took 11 different image fields from the Galaxy Evolution Explorer (GALEX) satellite’s telescope to produce this gorgeous portrait of the spiral galaxy in ultraviolet light. While its spiral arms stand out in visible light images of Andromeda (also known as M31), the arms look more like rings in the GALEX ultraviolet view, dominated by hot, young, massive stars. As sites of intense star formation, the rings have been interpreted as evidence Andromeda collided with its smaller neighboring elliptical galaxy M32 more than 200 million years ago. The large Andromeda galaxy and our own Milky Way are the dominant members of the local galaxy group. (via Astronomy Picture of the Day)
