Experimental study of parameters of X-ray radiation from solar flares using the PENGUIN-M instrument aboard the CORONAS-PHOTON spacecraft

The main characteristics of the PENGUIN-M instrument are given. The instrument has been operating aboard the CORONAS-PHOTON spacecraft (SC) launched into orbit on January 30, 2009. The instrument includes the PENGUIN-MD detector unit (PMD) and the PENGUIN-ME electronic unit (PMD). The purpose of the experiment is to measure the degree of linear polarization of X-ray radiation from solar flares in the energy range of 20–150 keV and to obtain energy spectra of X-ray radiation from solar flares in the energy range of 2–500 keV. The paper describes the instrument, calibration procedure, and in-flight adjustment, and contains the first results of measurements.     

Stereoscopic observations of solar flares made onboard the 2001 Mars Odyssey spacecraft and CORONAS-F satellite

The results of observations of solar hard radiation recorded by two spacecraft—2001 Mars Odyssey and CORONAS-F—which were located in the vicinity of Mars and Earth, respectively, are discussed. The HEND instrument, developed at the Space Research Institute of the Russian Academy of Sciences, recorded photons with energies ranging from 80 keV to 2 MeV, and the SPR and SONG instruments, developed at the Skobeltsyn Research Institute of Nuclear Physics of the Moscow State University, detected radiation in the energy interval from 15 keV to 100 MeV. The rising of the sunspot group 10486 in late October 2003, which had been observed from Martian orbit before it was seen from the Earth’s surface, is analyzed in detail. In this case, observations made from directions that differ by 24° showed a close-to-24 h advance for the detection of hard radiation of flares. Stereoscopic observations of M-class flares near the limb show that the overwhelming part of radiation with energies above 80 keV arises at heights that do not exceed 7–10 thousand km. Also reported are the results of observations of the powerful flare on August 25, 2001, by the two devices, which complement each other substantially. The processes resulting in the formation of high-energy radiation of solar flares are discussed.     

First ENA observations at Mars: Solar-wind ENAs on the nightside

We present measurements with an Energetic Neutral Atom (ENA) imager on board Mars Express when the spacecraft moves into Mars eclipse. Solar wind ions charge exchange with the extended Mars exosphere to produce ENAs that can spread into the eclipse of Mars due to the ions' thermal spread. Our measurements show a lingering signal from the Sun direction for several minutes as the spacecraft moves into the eclipse. However, our ENA imager is also sensitive to UV photons and we compare the measurements to ENA simulations and a simplified model of UV scattering in the exosphere. Simulations and further comparisons with an electron spectrometer sensitive to photoelectrons generated when UV photons interact with the spacecraft suggest that what we are seeing in Mars' eclipse are ENAs from upstream of the bow shock produced in charge exchange with solar wind ions with a non-zero temperature. The measurements are a precursor to a new technique called ENA sounding to measure solar wind and planetary exosphere properties in the future.     

A study of the Northern polar region of the sun using the microwave observations of the total eclipse of March 29, 2006

We report the results of unique observations of the solar eclipse of March 29, 2006 over a wide radio-wavelength range from 1 to 50 cm made with the large RATAN-600 stationary radio telescope during the maximum eclipse phase performed using the method of the source transit across the fixed beam pattern. The multifunctional opportunities of the radio telescope allowed observations to be performed simultaneously in a part of the Northern sector of RATAN-600 and in the Southern-sector plus periscope mode using all the available receiving equipment at the corresponding secondary mirrors. At the time of maximum eclipse phase a narrow 1—3-arcsec wide crescent-shaped band near the North Solar Pole remained visible out of the entire solar disk covered by the Moon. We achieved high flux sensitivity, which allowed us to discover a large polar radio source located above the North Solar Pole and obtain detailed data on its radiation and spatial structure. Moreover, we detected optically thin radiation of the solar corona at the brightness-temperature level of several K or several tens of K. We find this radiation to extend beyond the solar limb out to the heliocentric distances of one solar radius. These data are unique in that they are not contaminated by scattered radiation of the solar radio disk, which usually shows up in ordinary observations. We are the first to obtain a detailed spectrum of the radiation of a high-latitude prominence at many wavelengths with a 1% frequency resolution in the microwave range, which allowed us to estimate its magnetic field at a number of levels in the lower corona.     

Photoelectric study of the sky brightness along Sun’s meridian during the March 29, 2006 solar eclipse

Photoelectric observations of the sky brightness along Sun’s meridian have been carried out at Salloum during the March 29, 2006 total solar eclipse. The measurements have been taken at different zenith distances along the Sun’s meridian using yellow and red wide band glass filters centered at 5500 Å and 7900 Å, respectively. The present results of the sky brightness during the total solar eclipse have been compared with that of twilight, and night sky obtained by the same instrument at Abu-Simbel and Kottamia observatory sites respectively. The variation of V–R color index with zenith distance have been also studied. The visibility of planets and stars during the March 29, 2006 total solar eclipse is given.     

Ultraviolet, hard X-ray, and gamma-ray emission of solar flares recorded by VUSS-L and SONG instruments in 2001–2003

The results of simultaneous measurements of variations of UV radiation (in a band near the hydrogen L_α line, 121.6 nm) and hard X-ray and gamma-ray radiation (50 keV-200 MeV) performed by the VUSS-L and SONG instruments, respectively, onboard the CORONAS-F spacecraft are presented for periods of solar flares. Variations in the L_α ultraviolet radiation during the impulsive phase of a flare are shown to be synchronous with those of hard X-ray radiation. Temporal variations of UV and X-ray fluxes correspond to the progressive heating of higher and higher regions of the solar atmosphere and the energy transfer from the lower layers of the solar atmosphere to the coronal areas of flare regions. The energy of electrons in beams arising during the impulsive phase of flares can be as high as 500 keV. The velocity of the energy propagation from the regions of its release to the upper layers of the solar atmosphere can reach several tens of kilometers per second.     

Properties of the noise storm source at wavelength 1 m from observations of the solar eclipse on March 29, 2006

Observations of the solar eclipse on March 29, 2006, at the Laboratory of Radio Astronomy of the CrAO showed that the radio radius of the Sun at a wavelength of 1 m in the direction of the first contact was R _d = 1.12 R _⊙ during solar activity minimum between cycles 23 and 24. The brightness temperature of the undisturbed Sun was T _d = (0.6 ± 0.06) × 10⁶ K. There was a noise storm source above the sunspot group NOAA 0865 whose bright nucleus had a size of 1′.3 and a brightness temperature T _b = 16 × 10⁶ K. The noise storm bursts were emitted from the region of the bright nucleus above the group NOAA 0865 and were absent during its covering by the disk of the Moon. Thermal radiation from a coronal condensation with a brightness temperature of (1?2) × 10⁶ K extending out from the visible solar disk to 2′.7 was observed during the eclipse above the eastern limb sunspot group NOAA 0866. The bright nucleus in this limb source appeared 42 min after eclipse termination and persisted in the ensuing days. This may be indicative of the time of its emergence from behind the radio horizon formed by regular refraction of radio waves in the corona. The refractive displacement was measured by comparison with the eclipse observations at a shorter wavelength of 12 cm. Its value of 0′.96 is close to the calculated value of 0′.8.     

Observations and discussions concerning ‘high’ polarization features in the solar corona

Photographic observations were obtained of the radial and tangential polarization of the solar corona for the 1970, March 7, solar eclipse. The corona was photographed using a neutral density filter and rotating linear polaroid sectors to allow the polarization structure to be seen from 1 to 6 solar radii. Anomalously high polarizations were found for structures with the E-tangential intensity being predominantly larger than the E-radial intensity. These structures are generally filamentary in nature and radial in direction. One case with a high radial polarization was also found. The photographs were calibrated accurately against the Earth shine from the Moon. Possible source mechanisms are discussed that may explain this new component in the solar corona. Most sources may be ruled out on physical grounds. One possibility appears to be synchrotron radiation from 10 GeV electrons in a 0.4 G field. The existence of these electrons, however, is unlikely in that spacecraft observations at 1 AU do not confirm their presence.     

Perturbing effect of solar radiation on the Spektr-RG spacecraft in operational orbit

Results and analysis are presented for a numerical simulation of solar radiation forces acting on the Spektr-RG spacecraft in operational orbit. The possibility is investigated of compensating the radiation pressure-induced perturbing torque without adding new units and assemblies into the spacecraft configuration. A rationale is given for ways of implementing the compensation techniques that enable 65% compensation of sufficiently large perturbing torques, thus considerably reducing (by 5–6 kg) the propellant consumption in the control system engines and increasing the lifetime of the spacecraft.     

The Plate Scale of the SODISM Instrument and the Determination of the Solar Radius at 607.1 nm

Knowledge of the Solar Diameter Imager and Surface Mapper (SODISM) plate scale is a fundamental parameter for obtaining the solar radius. We have determined the plate scale of the telescope on the ground and in flight onboard the Picard spacecraft. The results show significant differences; the main reason is that the conditions of observation are not the same. In addition, the space environment has an impact on the performance of a metrology instrument. Therefore, calibration in space and under the same conditions of observation is crucial. The transit of Venus allowed us to determine the plate scale of the SODISM telescope and hence the absolute value of the solar radius. The transit was observed from space by the Picard spacecraft on 5?–?6 June 2012. We exploited the data recorded by SODISM to determine the plate scale of the instrument, which depends on the characteristics of optical elements (mirrors, filters, or front window). The mean plate scale at 607.1 nm is found to be 1.0643 arcseconds?pixel^?1 with 3×10^?4 RMS. The solar radius at 607.1 nm from 1 AU is found to be equal to 959.86 arcseconds.     

PHOKA experiment: Description of the equipment and first results

The CORONAS-PHOTON Russian satellite intended to study the Sun was successfully launched into orbit on January 30, 2009. Scientific equipment of the satellite includes the PHOKA radiometer of soft X-ray and extreme UV radiation. The PHOKA instrument is intended to measure the absolute flux of solar electromagnetic radiation in the spectral windows of 0.5–7 nm, 0.5–11 nm, 27–37 nm, and 116–125 nm. When leaving and entering the Earth’s shadow, the instrument aboard the spacecraft measures absorption of radiation by various layers of the Earth’s atmosphere. Before the launch, photodiodes of the instrument had been calibrated using a synchrotron radiation source. In-flight stability of sensitivity of main channels is controlled using calibration channels. The paper describes the PHOKA instrument and presents its capabilities and main characteristics, as well as some results of its operation in orbit.     

Problem “13” for geostationary spacecraft

We consider the problem of ensuring an energy balance of geostationary spacecraft (SCs) that will arise on October 13, 2015, during the long-duration eclipse of the solar disk visible from the SC by the Moon and the Earth. A technique for assessment of the eclipse duration, taking into account the shaded area of visible solar disk, is set forth, and results of calculating the eclipse conditions for different SC “stationary” points in the geostationary orbit are given. The data presented will allow the specialists to be prepared in advance for specific ballistic conditions of SC operation at this date and to plan operations to ensure the power balance of the SC power supply system during the prolonged shading of the Sun by the Moon and the Earth.     

A polarization-intensity anticorrelation diagram for the solar coronal green line

We analyze the complex pattern of anticorrelation between the degree of polarization p in the green λ530.3-nm line and its intensity I _λ, which was revealed by coronal observations during the total solar eclipse of July 11, 1991. For coronal points located at approximately the same distance from the disk center, the anticorrelation diagram breaks up into two branches with a zone of avoidance between them. High-latitude streamers form the upper branch, while the lower branch belongs to active equatorial regions. The arrangement of large-scale coronal structures in the p-logI _λ diagram is considered for a distance of 1.2R _⊙. The change in anticorrelation diagram with distance is analyzed in detail for the giant high-latitude coronal streamers observed on July 11, 1991. Our results contain important information about the scattering of photospheric radiation at line frequencies in the presence of a coronal magnetic field.     

Airborne total eclipse observation of the extreme solar limb at 400 μm

The total solar eclipse of February 26, 1979 was monitored at far infrared wavelengths from the NASA Lear Jet Observatory flying at 12.9 km in the eclipse shadow. The resultant eclipse curve for radiation within a bandwidth of 20 cm^–1 centered upon 25 cm^–1 (400 m) was measured and analysed at an equivalent angular resolution of 1 arc sec over a 100 arc sec region adjacent to the limb to provide information on the intensity distribution of continuum radiation close to this limb. The curve has been compared to predictions derived from models of the solar atmosphere for the specific geometry of this eclipse, and is shown to match most closely that derived from a uniform distribution of radiation across the disk. This is in distinct contrast to the result obtained in the only other comparable experiment, carried out over Africa in 1973 from a supersonic Concorde aircraft, in which an intense but narrow spike of far infrared radiation at the extreme solar limb was inferred from the data. The absence also in the present observations of the significant limb brightening predicted by the HSRA model (in which homogeneity within the source region is assumed) is in substantial agreement with lower resolution results from mountain altitudes. This result is interpreted as further evidence for the presence in the Sun's lower chromosphere of significant inhomogeneity with a scale size of at least 1000 km at this depth.     

On the variation of the direct solar radiation during the annular solar eclipse of April 29, 1976

Measurements of the direct solar radiation during the annular solar eclipse of April 29, 1976 are given in three wavelength bands (centered on 800, 680, and 450 nm). A decrease of the solar radiation after the last contact was observed, especially in the red and infrared. This is considered in connection with the results of other direct light and zenith light measurements.     

Ionospheric currents and fields during the solar eclipse

We calculate electric fields and currents in the ionosphere during the solar eclipse. Three dimensional anisotropic and inhomogeneous conductivity distribution is taken into consideration. Electrical conductivity is assumed to be decreased by the solar eclipse, but winds are not altered. It is shown that the additional currents and fields due to the eclipse are essentially understood as those generated by the obstruction to Sq currents. However, the currents flow preferably in the region nearer to the noon meridian and at the Equator and partly escape through the field-aligned currents to the opposite hemisphere, and therefore the effect of the solar eclipse is also seen in the opposite hemisphere in the deformed shape.     

Parameters of the intense X-ray and gamma-ray radiation from the solar flare of May 20, 2002, as observed from the Coronas-F spacecraft

We consider temporal, spectral, and polarization parameters of the hard X-ray and gamma-ray radiation observed during the solar flare of May 20, 2002, in the course of experiments with the SONG and SPR-N instruments onboard the Coronas-F spacecraft. This flare is one of the most intense gamma-ray events among all of the bursts of solar hard electromagnetic radiation detected since the beginning of the Coronas-F operation (since July 31, 2001) and one of the few gamma-ray events observed during solar cycle 23. A simultaneous analysis of the Coronas-F and GOES data on solar thermal X-ray radiation suggests that, apart from heating due to currents of matter in the the flare region, impulsive heating due to the injection of energetic electrons took place during the near-limb flare S21E65 of May 20, 2002. These electrons produced intense hard X-ray and gamma-ray radiation. The spectrum of this radiation extends up to energies ≥7 MeV. Intense gamma-ray lines are virtually unobservable against the background of the nonthermal continuum. The polarization of the hard X-ray (20–100 keV) radiation was estimated to be ≤15–20%. No significant increase in the flux of energetic protons from the flare under consideration was found. At the same time, according to ACE data, the fluxes of energetic electrons in interplanetary space increased shortly (～25 min) after the flare.     

Joint computation of aerodynamic and radiation forces acting on spacecraft

A methodology is presented for the joint computation of aerodynamic and radiation forces acting on orbital spacecraft. Special attention is given to the computation of the radiation component. The reliability of the results is confirmed by comparing them with those obtained by other methods and flight measurements. Results are presented of a study of the combined impact induced by solar radiation and the upper atmosphere on the small spacecraft MKAFKI (Zond-PP).     

Observation in Crimea of solar eclipse on August 1, 2008, at wavelengths 10.5 and 12 cm in the epoch of minimum of solar activity

The analysis of observations of the eclipse on August 1, 2008, at wavelengths of 10.5 and 12 cm demonstrated that, in the epoch of deep minimum between the 23rd and 24th cycles of solar activity, the radio radius of the solar disk in the equatorial direction was 120 × 10³ km larger than the radio radius in the polar direction. In this case, the brightness temperature of the polar region turned out to be of the order of (35–37) × 10³ K and corresponded to the radiation emission from upper layers of the chromosphere from an altitude of about 11 × 10³ km. At the heliolatitude <25° beyond the visible disk at a distance of about 70 × 10³ km from the photosphere an increased radio brightness of up to 100 × 10³ K was observed, which testifies to the increased electron density in the equatorial zone of the corona at the complete absence of groups of spots on the solar disk.     

Sun,earth and sky

The Sun is enveloped by a hot, tenuous million-degree corona that expands to create a continuous solar wind that sweeps past all the planets and fills the heliosphere. The solar wind is modulated by strong gusts that are initiated by powerful explosions on the Sun, including solar flares and coronal mass ejections. This dynamic, invisible outer atmosphere of the Sun is currently under observation with the soft X-ray telescope aboard the Yohkoh spacecraft, whose results are presented. We also show observations from the Ulysses spacecraft that is now passing over the solar pole, sampling the solar wind in this region for the first time. Two other spacecraft, Voyager 1 and 2, have recently detected the outer edge of the invisible heliosphere, roughly halfway to the nearest star. Magnetic solar activity, the total radiative output from the Sun, and the Earth's mean global surface temperature all vary with the 11-year sunspot cycle in which the total number of sunspots varies from a maximum to a minimum and back to a maximum again in about 11 years. The terrestrial magnetic field hollows out a protective magnetic cavity, called the magnetosphere, within the solar wind. This protection is incomplete, however, so the Sun feeds an unseen world of high-speed particles and magnetic fields that encircle the Earth in space. These particles endanger spacecraft and astronauts, and also produce terrestrial aurorae. An international flotilla of spacecraft is now sampling the weak points in this magnetic defense. Similar spacecraft have also discovered a new radiation belt, in addition to the familiar Van Allen belts, except fed by interstellar ions instead of electrons and protons from the Sun.