Prominences of the Active and Sun-Spot Types Compared
Abstract
Tue tower ielescope.-The 50-foot tower telescope at Lake Angelus, Pontiac, Michi- gan, records solar phenomena by means of the motion-picture camera. All instru- mental motions are electrically driven; the coelostat flat and camera are operated by the McMath-Hulbert controlled frequency drive and declination control. The scout camera and spectral-line control .-B oth H and K are used, K for the motion- picture camera; the H line, thrown to one side, enters a plate camera so that a promi- nence under observation can be photographed and developed for inspection at any time. To set the H and K lines on the slits of the spectroheliograph and to check their posi- tions an auxiliary fixed slit fed by a mercury arc is used. Observing and measuring-For the bulk of the work a focal length of 40 feet was used for the solar image. Exposure is determined by a photronic photometer and is usually of the order of 20-25 seconds on prominences with 2~ seconds between expo- sures. The films are measured by projecting the frames upon a milk-glass screen; the position of a knot or streamer along its trajectory is determined with a flexible celluloid scale or, in some cases where the motion is small, by a cathetometer. Activity within a sun-spot group.-The ejection of bright flocculi has been observed. The velocity is about 100 km/sec, and the phenomenon occurs at intervals of about an hour. Prominences of the sun-spot type-Detailed measurements of the motions of knots and loop ends along their trajectories show that class III prominences obey the first law of motion of eruptive prominences and, when the projection factor is small, the sec- ond law as well. Many streamers have their origin high above the chromosphere, and the appearance cannot be accounted for by Doppler effect. The simplest explanation requires the presence of a chromospheric atmosphere in the corona. Surges-These rise from and sink back into the chromosphere in the vicinity of sun-spots, forming class hId. They are mostly small, but one was observed which reached a height of 8o,ooo km with a velocity of 240 km/sec. The ftrst law of motion seems to prevail in this type also. Quasi-eruptions-A case where an active prominence rose to a great height, nearly reaching the eruptive stage, before being drawn back to the center of attraction is cited. This forms a connecting link between active and eruptive prominences and sub- stantiates the idea that eruptions are extreme cases of the active or class Ilic stages. Active prominences.-Detailed measurements on these prominences show that the streamers and knots move along their trajectories, obeying both laws of motion of eruptive prominences
- Publication:
-
The Astrophysical Journal
- Pub Date:
- May 1937
- DOI:
- 10.1086/143824
- Bibcode:
- 1937ApJ....85..279M