Solar Radiation of Wavelength 1.25 Centimetres

1949 ◽  
Vol 2 (4) ◽  
pp. 539
Author(s):  
U Radok
Keyword(s):  
Solar Activity ◽  
Solar Radiation ◽  
Michelson Interferometer ◽  
Black Body ◽  
Maximum Error ◽  
Average Intensity ◽  
Observational Accuracy ◽  
Short Period ◽  
Uniform Disk ◽  
Narrow Ring

Observations of solar radiation at a wavelength of 1.25 cm. and covering a period of about six months are described. The average intensity of radiation corresponded to a black-body temperature of 1.00 x 104 �K. with a maximum error of about � 5 per cent. Day-to-day variations in intensity were less than � 3 per cent., which was the limit of observational accuracy. Short-period fluctuations were observed on a few occasions ; even during periods of intense solar activity they were not greater than � 5 per cent. The distribution of intensity over the solar disk was measured by a method analogous to the Michelson interferometer technique and found to be consistent with 84 per cent. of the radiation coming from a uniform disk and 16 per cent. from a narrow ring around the circumference.

Solar Radiation at a Wavelength of 3.18 Centimetres

1950 ◽  
Vol 3 (1) ◽  
pp. 60 ◽  
Author(s):  
HC Minnett ◽  
NR Labrum
Keyword(s):  
Body Temperature ◽  
Solar Radiation ◽  
Black Body ◽  
Sunspot Area ◽  
Probable Error ◽  
The Sun ◽  
Solar Origin ◽  
Unit Increase ◽  
Uniform Disk ◽  
Visible Disk

Solar radiation at a wavelength of 3.18 cm. has been measured over a period of three months. The received intensity was found to vary from day to day and the changes are shown to be closely associated with sunspots. The equivalent black-body temperature of the sun over this period, in the absence of sunspots, was 19,300 �K., with a probable error of �7 per cent. The temperature increased by 8 �K. per unit increase of sunspot area (one unit equals 10-5 times the area of the sun's visible disk). This increase is much less than that at longer microwavelengths. Sudden increases of radiation at 3.18 cm., caused by disturbed conditions in the sun, were found to be rare. A number of bursts were observed and a comparison is made with records of longer wave solar radiation and other phenomena of solar origin. Observations were made during the solar eclipse of November 1, 1948 and the results are consistent with either of two simple brightness distributions on the sun's disk. In the first of these, 74 per cent. of the energy is emitted uniformly by the sun's visible disk and the remaining 26 per cent. by a bright ring around the circumference ; in the second, the whole of the radiation comes from a uniform disk of diameter 1.1 times that of the visible sun.

Evolution of Comets into Asteroids?

1971 ◽  
Vol 12 ◽  
pp. 413-421 ◽  
Author(s):  
B.G. Marsden
Keyword(s):  
Solar Radiation ◽  
Solar Nebula ◽  
Oort Cloud ◽  
Original Version ◽  
Terrestrial Planets ◽  
Minor Planets ◽  
The Sun ◽  
Physical Difference ◽  
Short Period ◽  
The One

There has long been speculation as to whether comets evolve into asteroidal objects. On the one hand, in the original version of the Oort (1950) hypothesis, the cometary cloud was supposed to have formed initially from the same material that produced the minor planets; and an obvious corollary was that the main physical difference between comets and minor planets would be that the latter had long since lost their icy surfaces on account of persistent exposure to strong solar radiation (Öpik, 1963). However, following a suggestion by Kuiper (1951), it is now quite widely believed that, whereas the terrestrial planets and minor planets condensed in the inner regions of the primordial solar nebula, icy objects such as comets would have formed more naturally in the outer parts, perhaps even beyond the orbit of Neptune (Cameron, 1962; Whipple, 1964a). Furthermore, recent studies of the evolution of the short-period comets indicate that it is not possible to produce the observed orbital distribution from the Oort cloud, even when multiple encounters with Jupiter are considered (Havnes, 1970). We must now seriously entertain the possibility that most of the short-period orbits evolved directly from low-inclination, low-eccentricity orbits with perihelia initially in the region between, say, the orbits of Saturn and Neptune, and that these comets have never been in the traditional cloud at great distances from the Sun.

scholarly journals A Methodology for Modelling of Steady State Flow in Pelton Turbine Injectors

2019 ◽  
Vol 15 (2) ◽  
pp. 246-255
Author(s):  
Tri Ratna Bajracharya ◽  
Rajendra Shrestha ◽  
Ashesh Babu Timilsina
Keyword(s):  
Velocity Profile ◽  
High Speed ◽  
Three Dimensional ◽  
Maximum Error ◽  
Cfd Modelling ◽  
Pelton Turbine ◽  
Short Period ◽  
Computational Fluid Dynamics Cfd ◽  
Jet Velocity ◽  
Nozzle Opening

 Pelton turbine is a high head-impulse type turbine. The high-speed jet strikes the symmetrical semi ellipsoidal buckets, thus transferring the momentum within short period of time, impulse. The conversion of potential energy of water to kinetic energy in the form of jet is done by a nozzle with internally fitted spear or needle, the assembly in known as injector. The jet quality includes but is not limited to jet velocity, velocity distribution ‘velocity profile’, core location etc. In this study, the modeling of flow in Pelton turbine injector is done by commercial Computational Fluid Dynamics (CFD) solver on a three-dimensional flow domain. The results obtained from CFD modelling are then compared against the experimental observations and previously published literatures. The jet streamline, jet velocity profile and jet core location are then studied. As observed experimentally, the mean jet diameter reduces as the nozzle opening decreases. In addition, like the experimental observations, the jet first contracts and then expands. The diameter of the contraction is then normalized with nozzle exit diameter and is plotted for both experimental observations as well as the results of the numerical simulation. The maximum error between experimental and numerical analysis of jet contraction is 20%. The jet core is located at region axially ahead of needle tip.

Solar Radiation at 1200 MC/S., 600 MC/S., and 200 MC/S

1949 ◽  
Vol 2 (1) ◽  
pp. 48 ◽  
Author(s):  
FJ Lehany ◽  
DE Yabsley
Keyword(s):  
Magnetic Field ◽  
Body Temperature ◽  
Solar Radiation ◽  
Thermal Emission ◽  
Black Body ◽  
Sunspot Area ◽  
The Sun ◽  
Long Period ◽  
Period Variations ◽  
The Magnetic Field

Daily observations of solar radiation at frequencies of 1200 Mc/s., 600 Mc/s., and 200 Mc/s. taken between August 18 and November 30, 1947, are described. The characteristics of the radiation at 200 Mc/s. were in general agreement with those observed by earlier workers. At 600 Mc/s. and 1200 Mc/s., the received intensity was normally steady on any one day but underwent long-period variations over a range of about two to one. The radiation received when the sun was almost free of sunspots corresponded to an effective black-body temperature of 0.5 million �K. at 600 Mc/s. and 0.1 million �K. at 1200 Mc/s. As sunspots appeared, the temperature rose and showed marked oar- relation with sunspot area. It is considered that radiation at these frequencies is entirely thermal in origin and that the long-period variations are at least partly due to the influence of the magnetic field of sunspots on the mechanism of thermal emission from a magneto-ionic medium. On a few occasions, isolated disturbances were observed on 600 Mc/s. and 1200 Mc/s. some of which were associated with chromospheric flares and radio fade-outs. The difficulties arising in the calibration of the apparatus and the steps taken to overcome them are discussed in detail.

A study of short-period variation in solar activity

2014 ◽  
Vol 14 (8) ◽  
pp. 1011-1018
Author(s):  
Ji-Long Chen ◽  
Juan Zhao
Keyword(s):  
Solar Activity ◽  
Period Variation ◽  
Short Period

scholarly journals Division II: The Sun and Heliosphere: (Le Soleil et Heliosphere)

2000 ◽  
Vol 24 (1) ◽  
pp. 65-66
Author(s):  
Peter Foukal ◽  
Guoxiang Ai ◽  
Arnold Benz ◽  
Oddbjorn Engvold ◽  
Sami Solanki ◽  
...  
Keyword(s):  
Solar Activity ◽  
Solar Radiation ◽  
Executive Committee ◽  
The Sun ◽  
Present Structure ◽  
Interplanetary Plasma ◽  
Division Ii ◽  
The Individual

Division II consists of Commissions 10 (Solar Activity), 12 (Solar Radiation and Structure), and 49 (Interplanetary Plasma and Heliosphere). More detailed information on IAU activities in each of these three areas can be found in the individual reports of the respective Commissions.The Division II OC briefly considered changes to the structure of our Division in response to opportunities offered by the Executive Committee during this triennium. However, we believe that the present structure works well and change is not warranted at this time.

Abrupt shrinking of solar corona in late 1990s and related changes in solar magnetic structure

2020 ◽  
Author(s):  
Kalevi Mursula ◽  
Ilpo Virtanen ◽  
Jennimari Koskela ◽  
Ismo Tähtinen
Keyword(s):  
Magnetic Field ◽  
Solar Activity ◽  
Solar Corona ◽  
Coronal Magnetic Field ◽  
Systematic Change ◽  
Time Interval ◽  
Source Surface ◽  
Abrupt Decrease ◽  
Heliospheric Magnetic Field ◽  
Short Period

<p>Several studies have noted on changes in the properties of sunspots, and in the mutual relations between various global parameters of solar magnetic activity (e.g. UV/EUV irradiance, radio and IR emissions, TSI/SSI), as well as between solar and ionospheric parameters since the onset of solar cycle 23. These changes have been suggested to be related to the overall reduction of solar activity at the aftermath of the decline of the Grand modern maximum of solar activity that prevailed during most of the 20th century. We have recently derived the longest record of coronal magnetic field intensities since 1968 using Mount Wilson Observatory and Wilcox Solar Observatory observations of the photospheric magnetic field and the PFSS model, and compared it with the heliospheric magnetic field observed at the Earth. We found that the time evolution of the coronal magnetic field during the last 50 years agrees with the heliospheric magnetic field only if the effective coronal size, the distance of the coronal source surface of the heliospheric magnetic field, is allowed to change in time. We calculated the optimum distance for each solar rotation and found that it experienced an abrupt decrease in the late 1990s. The effective volume of the solar corona shrunk to less than one half of its previous value during a short period of only a few years. This shrinking was related with a systematic change in the structure of the coronal magnetic field during the same time interval. We review these dramatic changes in the solar corona and discuss their possible connection to the changes in the different solar activity parameters and the reduction of the overall solar activity.</p>

The effects of solar radiation and black body re-radiation on thermal comfort

Ergonomics ◽  
2008 ◽  
Vol 51 (4) ◽  
pp. 476-491 ◽  
Author(s):  
Simon Hodder ◽  
Ken Parsons
Keyword(s):  
Solar Radiation ◽  
Thermal Comfort ◽  
Black Body

scholarly journals An investigation of radio-frequency radiation from the sun

1948 ◽  
Vol 193 (1032) ◽  
pp. 98-120 ◽  
Keyword(s):  
Solar Radiation ◽  
Radio Frequency ◽  
Random Noise ◽  
Internal Noise ◽  
Black Body ◽  
Local Source ◽  
The Sun ◽  
Radio Frequency Radiation ◽  
Absolute Measurements ◽  
Frequency Radiation

It has been known for some time that the sun emits radio-frequency radiation whose intensity greatly exceeds the value expected from a black-body at 6000°K. In the present paper, experiments are described in which measurements have been made of the solar radiation at frequencies of 175 and 80 Mcyc. /sec. Measurement of the small powers which can be abstracted from practical aerial systems requires special types of receiving equipment if absolute measurements are to be recorded automatically over long periods of time. An apparatus has been developed in which the output power of a local source of random ‘noise’ is automatically and continuously adjusted so as to be equal to the aerial power; in this way the receiver is used only as an indicator of balance, and errors due to variation of its gain or internal noise are eliminated. A special type of aerial has been devised which enables the solar radiation to be recorded separately from the galactic radiation, and so enables continuous observation of the sun to be made with aerials of comparatively low directivity. The results obtained on these two frequencies show that the sun normally emits radiation whose intensity corresponds to a surface temperature of the order of 10 6 °K. Large fluctuations in the intensity occur, however, and during the passage of large sunspots, equivalent temperatures as high as 10 8 to 10 9 °K have been observed. In addition to these day-to-day variations the radiation is subject to sudden brief increases of intensity lasting only for a few seconds. Measurements of the diameter of the source, by a method analogous to Michelson’s stellar interferometer, have shown that during periods of very great intensity the radiation originates in an area of the sun of the same order of size as a sunspot. This result means that equivalent temperatures of 10 9 to 10 10 °K must exist. Measurements of the polarization of the radiation have shown that during periods of increased activity the radiation is mainly circularly polarized. The present account covers the experimental methods and the results obtained up to the present time. It is hoped to consider these results theoretically in a future paper.

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