Author name code: evans ADS astronomy entries on 2022-09-14 =author:"Evans, John W." OR =author:"Evans, J.W." year:1932-1993 -aff:"United Kingdom" -aff:"Wormley" ------------------------------------------------------------------------ Title: The birefringent filter (Journal of the Optical Society of America 1949) Authors: Evans, J. W. Bibcode: 1993inas.book...71E Altcode: No abstract at ADS Title: Hale Prize Lecture - Enjoyment in an Astronomical Occupation ( J. W. EVANS ) Authors: Evans, J. W. Bibcode: 1981BAAS...13..805E Altcode: No abstract at ADS Title: Sacramento Peak Observatory, Sunspot, New Mexico. Observatory report. Authors: Evans, J. W. Bibcode: 1977BAAS....9..243E Altcode: No abstract at ADS Title: Introductory Review of Solar Activity Authors: Evans, J. W. Bibcode: 1976saop.book....3E Altcode: No abstract at ADS Title: Observed Oddities in the Lines H, K, b and H&beta Authors: Evans, J. W.; Catalano, C. P. Bibcode: 1972SoPh...27..299E Altcode: We compare microphotometer intensity traces perpendicular to dispersion in simultaneous spectrograms of good spatial resolution traced at various Δλ's in each of the lines. Cross correlations between the different traces show the following: (a) For each ΔλK there is a corresponding Δλb1at which the coefficient of correlation, r, is a maximum, usually > 0.8. (b) No such high correlations are found between H and Hβ. (c) Comparison of traces in the continuum and at all observed Δλ's in K, H, b1, b2 show a range of Δλ's in each line over which r is very significantly negative, while Hβ shows no such peculiarity. Title: Introductory Review of Solar Activity Authors: Evans, John W. Bibcode: 1972PrAA...30....3E Altcode: No abstract at ADS Title: Solar Instrumentation (Part I) Authors: Evans, John W. Bibcode: 1971spas.conf...61E Altcode: No abstract at ADS Title: Introduction to Research on the Solar Corona Authors: Evans, J. W. Bibcode: 1971ASSL...27....1E Altcode: 1971psc..conf....1E No abstract at ADS Title: The Chromospheric Spectrum at the 1962 Eclipse Authors: Dunn, R. B.; Evans, J. W.; Jefferies, J. T.; Orrall, F. Q.; White, O. R.; Zirker, J. B. Bibcode: 1968ApJS...15..275D Altcode: A joint expedition of the High Altitude Observatory, Sacramento Peak Observatory, and the National Bureau of Standards obtained slitless spectrograms of the flash spectrum at the February 5,1962, total eclipse of the Sun. The spectrograms covered the wavelength range of about 3200 to 9100 A with a height resolution of 100 km. The spectrographic equipment, the observations, the photometric calibration procedures, and the methods adopted to reduce the large quantity of data are described. The results are presented in a set of tables that show the wavelength and identification (where known) of each of the 3500 lines recorded. A separate set of tables lists the intensity of each line at each height. The latter tables are ordered according to the element, ionization stage, and multiplet number associated with the line. Title: Color in Solar Granulation Authors: Evans, John W. Bibcode: 1968SoPh....3..344E Altcode: Pairs of spectra exposed simultaneously in the yellow and ultraviolet show exactly the same solar granulation in the two colors. This is contrary to Vassilyeva's earlier results. The difference is probably due to her neglect of atmospheric dispersion. Title: Summary of Nobel Symposium 9 Authors: Evans, J. W. Bibcode: 1968mmsf.conf..243E Altcode: No abstract at ADS Title: Princeton University Observatory report. Authors: Evans, J. W. Bibcode: 1967AJ.....72.1128E Altcode: No abstract at ADS Title: Solar Granules in the Ultraviolet and Yellow. Authors: Evans, John W. Bibcode: 1967AJ.....72S.795E Altcode: Studies of rms vertical velocities in the solar atmosphere, evidenced by local Doppler shifts in Fraunhofer lines, show a marked dependence on both line strength and the wavelength region. The rms velocities increase towards the ultraviolet, and with increasing line strength (i.e., with height in the solar atmosphere). This is a report of an investigation to determine whether the detail of photospheric granular structure also varies between widely separated wavelength regions. The observational material consists of four pairs of spectrograms showing good spatial resolution along the slit. Each pair consists of a short length of the spectrum centered at N3954 (UV) and another at N5888 (Y) exposed simultaneously. The spectrograph slit was carefully oriented perpendicular to the horizon, parallel to the small displacements caused by differential atmospheric refraction. Each UV frame was traced perpendicular to dispersion by a digital microdensitometer at five continuum wavelengths, and each Y frame at three wavelengths. The cross correlations between the four pairs are 0.85+0.02, and we conclude that the granular structure at N3954 is very nearly identical with that at N5888. This result directly contradicts that found by Vassiljeva (Solar Phys. 1,16,1966) from photoelectric scanning across the solar disk with a sensitive spot 0 "2 in diameter. She found that the correlation rapidly decreased with wavelength difference, and had a value of only about 0.1 for a span of 1900 A. The Sacramento Peak spectrograms showed a relative displacement along the slit of 2 "1 between the UV and y images due to atmospheric refractive dispersion. I suggest that the low correlations between the structures Vassilj eva recorded at widely different wavelengths are the result of the atmospheric dispersion. This would cause her 0 "2 sensitive spot to scan along parallel lines in different colors, the separation of which would increase with wavelength difference, and inclination to the vertical circle. Title: Sacramento Peak Observatory Authors: Evans, John W. Bibcode: 1967SoPh....1..157E Altcode: No abstract at ADS Title: Motions in the Solar Atmosphere Authors: Evans, John W. Bibcode: 1966ossg.book...77E Altcode: No abstract at ADS Title: Observational Study of the Dynamics of the Solar Atmosphere Authors: Evans, John W. Bibcode: 1965ASSL....3...52E Altcode: 1965pss..conf...52E No abstract at ADS Title: Inclined inhomogeneities in the solar photosphere Authors: Evans, John W. Bibcode: 1964ApNr....9...33E Altcode: No abstract at ADS Title: Inclined Inhomogeneities in the Solar Atmosphere. Authors: Evans, John W. Bibcode: 1964AJ.....69R.541E Altcode: Good spectrograms of undisturbed regions on the sun show a pattern of lengthwise threads representing granulation. I have measured the x positions (perpendicular to dispersion) of threads as a function of X distance from the center of the strong line Fe4383.6 from AX=0.2 A to the continuum, and at the centers of other lines nearby. The standard deviation of a single measure corresponds to +20 to +40 km on the sun for sharp or fuzzy threads. Inspection of many spectrograms showed that many threads are visible curved, as though the positions of the corresponding granules along the slit varied with A~. The measurements on one spectrogram covering 135 000 km on the sun showed the following thread characteristics: (a) The x displacements are symmetrical, having the same sign and magnitude on the blue and violet sides of the line. The sign of the displacement is quite random. (b) Of the 58 bright threads visible in the spectrogram, the x displacements of 39 were >~160 km; of 4, >~970 km; and the rms for all was 500 km. (c) The displacements are present in all Fraunhofer lines and are very strongly correlated with line strength for any single thread. (d) There is no systematic tendency for threads to become fuzzy in their curved portions. My interpretation of this behavior is that a curved thread represents a columnar inhomogeneity which is sharply inclined to the vertical along the slit direction. At different AX's (or at the centers of weaker lines) we see cross sections of the column at a series of different heights, and hence at different apparent x positions. Allowing a very liberal 500 km for the total height range, the statistics show that high inclinations of 45o are the normal thing for bright inhomogeneities. This ignores the uncomfortable fact that the observed displacements occur between 5 and 20 Doppler widths from the line core, where we might expect a very small height range, and little height discrimination. Title: Review of Publications- The Solar Corona edited Authors: Evans, John W. Bibcode: 1963JRASC..57..268E Altcode: No abstract at ADS Title: Vertical Motions at Different Heights in the Solar Atmosphere. Authors: Evans, John W. Bibcode: 1963AJ.....68R..72E Altcode: Although the vertical motions in the solar atmosphere responsible for the "wiggles" in Fraunhofer lines are largely oscillatory (Leighton, Noyes, and Simon, Astrophys. J. 135, 474,1962; Evans and Michard, ibid. 136, 493,1962) the instantaneous velocity field is random. The rms vertical velocity ~v increases systematically with the strength of the line measured, and hence with geometrical height on the sun (Evans and Michard, Astrophys. J. 135, 812,1962). We should therefore expect to find a decrease in ~v as we measure the velocities at increasing distances AX from the centers of strong high-level lines, where we see to lower levels in the solar atmosphere. The L)oppler shifts in the profiles of Hot, H~, D1, and b2 have been measured for at least 50 points alo~ig each line. The measured velocities show without exception the expected smooth decrease from a maximum near the line center to a value ~2' to ~` as great at the largest AX's ~t which velocities could be determined. Less exact measurements (by the method described by Evans and Michard) in fe 3856.4 and Ca II 8542 lead to a similar result. This finding tidies up our concept of the height dependence of ~. We can use ~v with some confidence as a tool for ordering the Fraunhofer lines according to effective height of origin, and to relate them to the height of absorption in the wings of the strong lines. We must remember, however, that the "effective height" of ~ line is not very clearly defined since the contribution function extends over a considerable height range, and differs somewhat from one line to the next. As an index to height, however, ~v has the merit of being a straightforward observational quantity depending only on mass motion, which must be the same in a given element of volume for all atoms regardless of their properties or the physical state of their envlronment. Title: Motions in the Solar Atmosphere Authors: Evans, John W. Bibcode: 1963S&T....25..321E Altcode: No abstract at ADS Title: Emission-Line Ratios in the Solar Corona. Authors: Aly, M. K.; Evans, J. W.; Orrall, F. Q. Bibcode: 1963ApJ...137.1313A Altcode: No abstract at ADS Title: Observational study of macroscopic inhomogeneities in the solar atmosphere. V. Statistical study of the time variations of the solar inhomogeneities Authors: Evans, J. W.; Michard, R.; Servajean, R. Bibcode: 1963AnAp...26..368E Altcode: No abstract at ADS Title: The solar corona Authors: Evans, John W. Bibcode: 1963soco.conf.....E Altcode: 1963QB529.S6....... No abstract at ADS Title: A Photometric Study of the Continuum and Seventeen Emission Lines in the Inner Solar Corona. Authors: Aly, M. K.; Evans, J. W.; Orrall, F. Q. Bibcode: 1962ApJ...136..956A Altcode: Absolute intensities of the continuum and a number of emission lines between x 3300 and X 6800 have been measured as a function of position angle on spectrograms of the inner corona obtained by B. Lyot and M. K. Alyat the total eclipse of February 25,1952, at Khartoum. More detailed measurements were made in a bright coronal condensation on the west limb, where the continuum and the following emission lines were measurable: XX 3328, 3388, 3454, 3534, 3601, 3643, 3801, 3988, 4086, 4232, 4412, 5116, 5303, 5445, 5694, 6374, 6702. On the assumption that the condensation is axially symmetric, we have found the electron density and the emission as functions of distance from the axis of symmetry. The lines of lowest ionization potential show a decrease in emission at the center of the condensation while the continuum and the emission of the remaining lines show increasing concentration toward the center with increasing ionization potential. (An exception is X 3643, which behaves like a line of lower ionization potential than Ni xui.) X 3534 appears to be much too bright to be due to V x unless the abundance of vanadium is very much higher than current estimates for the photosphere. Title: Correlations in the Time Variations of Macroscopic Inhomogeneities in the Solar Atmosphere. Authors: Evans, J. W.; Main, P.; Michard, R.; Servajean, R. Bibcode: 1962ApJ...136..682E Altcode: No abstract at ADS Title: Observational Study of Macroscopic Inhomogeneities in the Solar Atmosphere. III. Vertical Oscillatory Motions in the Solar Photosphere. Authors: Evans, J. W.; Michard, R. Bibcode: 1962ApJ...136..493E Altcode: We have studied the Doppler displacements in two time sequences of spectrograms, one showing Fe I 5171.61, Mgi 5172.70 (b2), and Tii 5173.75 at the center of the solar disk, the other showing Fei 5324.19 at the limb. At the center we find that the velocity field consists mainly of short-lived oscillations of small elements of the solar atmosphere. The r.m.s. velocity amplitudes are 0.42 and 0.81 km/sec at low and high levels, respectively. The periods of the vertical oscillations cover roughly the range seconds, with a mean value around 242 sec. The periods seem to decrease with height in the atmosphere. An autocorrelation study shows also that the vertical velocity field is dominated by periodic oscillations, the time-correlation function having a strong positive peak at 300 seconds from the origin. The study of the time lags of oscillations between strong and faint lines suggests that they are of a type intermediate between progressive sonic waves (for the shorter periods) and standing waves (for the longer periods). Gradual transition from the first type to the second seems to occur during the life of a given oscillation. There is an indication that the individual oscillations are associated with individual granules. Near the limb, the observed horizontal motions consist of slowly changing velocities of the order of 0.5 km/sec in large surface elements, on which are superposed smaller random velocities of short duration. Oscillations rapidly disappear away from the center of the disk. The horizontal and vertical observable motions appear to be physically independent. Title: Observational Study of Macroscopic Inhomogeneities in the Solar Atmosphere. II. Brightness Fluctuations in Fraunhofer Lines and the Continuum. Authors: Evans, J. W.; Michard, R. Bibcode: 1962ApJ...136..487E Altcode: Large brightness fluctuations are observed at the centers of Fraunhofer lines of average and great strength. Their character is described for different lines and different parts of line profiles. Root-mean- square values are given for a number of cases. The scale of these features is comparable to the size of photospheric granulation. There are no simple relations between the brightness fluctuations in Fraunhofer lines, Doppler displacements of the lines, and continuum granulation. The bearing of these observations on recent inhomogeneous models of the photosphere is briefly discussed. Title: Observational Study of Macroscopic Inhomogeneities in the Solar Atmosphere. I. Velocity Displacements of Fraunhofer Lines as a Function of Line Strength and Position on Disk. Authors: Evans, J. W.; Michard, R. Bibcode: 1962ApJ...135..812E Altcode: The "random turbulent velocities," , of macroscopic motion in the solar atmosphere have been directly observed at the center of the disk as local Doppler displacements in 18 lines, ranging in Rowland intensity from 0 to 1000 (K3 line of Ca ii) The measurements show a marked increase of with line strength. On a given spectrogram, the correlation between the velocity shifts of one line with those of another line diminishes steadily as the intensity difference between the two lines increases. There is thus a quantitative and qualitative variation in the velocity field with height, as indicated by line strengths. The center-to4imb variations in were determined for four lines with Rowland intensities from 0 to 20. The strong and faint lines behave differently. The very pronounced increases of with line strength observed at the center of the disk disappears toward the limb. Here, within observational accuracy, is the same for all line strengths in the observed range. We suggest that the velocity field consists of a vertical component which increases strongly with height and a horizontal component independent of height. Title: The Solar Granulation Authors: Evans, J. W. Bibcode: 1962IAUTB..11..196E Altcode: No abstract at ADS Title: Local Doppler Effects in the Photosphere. Authors: Evans, John W.; Mauter, Horst Bibcode: 1961AJ.....66...42E Altcode: Highresolution spectrograms taken under conditions of good seeing at Sacramento Peak show the characteristic Doppler distortions of the solar Fraunhofer lines due to photospheric turbulence. The studies of Richardson and Schwarzschild (1950), Plaskett (1954), Goldberg, Mohler, Unno, and Brown (1960), and others, have fixed the directly resolvable dimensional characteristics and velocity distribution of the turbulent elements. This note reports the result of a first effort to determine the time variations. It is based upon a series of 31 spectrograms of the Fei line, x5324.2, taken at 20-sec intervals, and a 2-hr motion picture of the lines of Fei and Cri between A5327.5 and A5329.5, taken at a rate of 12 frames per minute. Isophotometer tracings of the 31 spectrograms yielded curves of velocity as a function of position in the solar image along the spectrograph slit. The mean length of a turbulent element along the slit was 3.1", while the smallest element observed was 1.2". The rms velocity in this small sample varied between 0.25 and 0.4 km/sec. The distribution of durations of individual velocity peaks, during which they develop and decay, is still uncertain, since a number of the larger peaks persisted throughout the 10-minute interval of observation. Longer observing intervals, with attention to the rotational motion of the solar surface past a fixed slit, will be necessary for a definitive result. The present observations, however, showed a marked positive correlation between the maximum velocity attained and the duration of a peak. The smallest duration observed with any confidence (with due regard for the uncertainties of guiding and seeing variations) was about two minutes, with a peak velocity of +0.5 km/sec. The motion pictures show the velocity fluctuations under rather mediocre seeing, and convey the impression of random velocity changes at any one point along the slit, with characteristic times of the order of three minutes. There were a few instances of a rather definite oscillation at one point between positive and negative velocities, going through as many as three complete cycles, with periods of about five minutes. Whether or not these are simply chance occurrences remains to be determined by a statistical study. Title: Flare-associated magnetic activity in the sun. Authors: Evans, John W. Bibcode: 1959AJ.....64R.330E Altcode: Observations of the longitudinal Zeeman effects in a solar active center show the variations of magnetic field streng~h during a period of 144 minutes on 30 April 1958, which included the development and decay of a flare of importance I ~. The measurements show that the flare crossed the neutral line of zero longitudinal field, and, although the extremities lay in regions of steep field gradients, most of the flare area was a region of low gradient. A small but pronounced S pole within the flare area developed and faded away in exact synchronism with the flare intensity. However, the large magnetic changes affected the whole field of the active center. The integrated magnetic energy of the region underwent a sharp decrease of about 16 per cent during the 14 minute rising phase of flare intensity, and an even sharper recoverN to its initial value immediately after flare maximum. This behavior was shared by the large sunspot fields and the area outside the sunspots. On the assumption that the field was 5000 km deep, the energy change of the active center amounted to 4 X I0~' ergs. The Ha radiation of the flare during its life was about 1028 ergs. Thus the changes in magnetic energy prob~bly exceed the total radiation of the flare in the Balmer and Lyman series by a considerable factor. Sacramento Peak Observatory Sunspot, New Mexico Title: Solar photographs from 80,000 feet. Authors: Schwarzschild, M.; Rogerson, J. B., Jr.; Evans, J. W. Bibcode: 1958AJ.....63..313S Altcode: During the summer of 1957 three unmanned balloon flights have been carried out with the aim of obtaining direct solar photographs with high definition, undisturbed by atmospheric seeing. The first flight had the purpose of testing the pointing mechanism and carried only a dummy telescope. The full telescope, constructed by Perkin-Elmer Co., carried on the second and third flights, consisted of a parabolic mirror of ~~-inch aperture, f/8, an enlarging lens which produced an effective focal length of 200 feet, and a 35-mm movie camera taking an exposure each second with exposure time 0~.00I. The focus was scanned over a range of 10 to 20 times the focus tolerance. In the pointing control which was constructed by the Research Service Laboratories of the University of Colorado, photo- diodes were employed to find the sun and center on it. Motor-driven magnetic clutches were used to move the telescope with the motion in azimuth being accomplished by rotating against a heavy flywheel carrying the batteries. In the execution of the flights, carried out by General Mills, Inc., no serious difficulties were encountered in the launching, tracking and recovering of the equipment. The cost of repairs for launching damage averaged for each of the three flights about 5 per cent of the construction cost. *Presented at the 99th A.A.S. meeting, Indianapolis, Ind., December 27-30, 1957. Several exposures of very high definition were obtained, both of the center of the solar disk and of the limb. These exposures show that the solar granulation has a cellular though highly irregular character. The bright cells appear separated from each other by dark, often very sharp lines. The sizes of the elements seem to range from 2" down to 0'.'3. This project was sponsored by the Office of Naval Research and the Geophysics Research Directorate of the Air Force. Princeton University Observatory, Princeton, N. J., and Sacramento Peak Observatory, Sunspot, N. M. Title: Instrumentation for Global Observation of the Sun during the IGY Authors: Evans, John W. Bibcode: 1958gigy.conf...21E Altcode: No abstract at ADS Title: Observations of the Solar Emission Corona Outside Eclipse Authors: Evans, John W. Bibcode: 1957PASP...69..421E Altcode: No abstract at ADS Title: The Sacramento Peak Observatory Authors: Evans, John W. Bibcode: 1956S&T....15..436E Altcode: No abstract at ADS Title: Solar Instrumentation Authors: Evans, J. W.; Dunn, R. B. Bibcode: 1956SCoA....1....5E Altcode: No abstract at ADS