The radiation environment encountered in space by satellites is extremely variable and depends mainly on the satellite position and space weather. Although models for the concerned processes are available, most of them only represent the average conditions and neglect the dynamics of the system. Accurate prediction of the radiation environment remains an unsolved problem. Space weather can cause manifold problems to spacecraft (S/C) components, such as degradation of sensors and solar arrays and changes in on-board memories by Single Event Upsets (SEU). The final effect is a degradation of the S/C overall performance and in extreme cases complete unavailability of services. When certain alarm conditions are reached, risk avoidance procedures may be invoked, e.g. switching off high voltages/biases/filters etc. and transition to protected operating modes. Once the detectors are off, there is just a rough estimation of when the conditions are safe again. Better prediction of radiation conditions and more accurate information could greatly improve these operations. Therefore it is necessary to monitor and predict the space weather effects and improve the space weather services.

Valuable large archive of solar radio observations has been accumulated by the Pulkovo solar radio group. But big part of data is recorded on paper. We describe a method and software for transferring data recorded on paper to FITS format.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

An aestimate of a typical life time of zebra pattern associated with escaping of fast particles from the trap into the loss-cone, is given. Besides, we estimate a number of fast electrons that is necessary to be injected into the trap in order to provide the observed brightness temperature of zebra stripes.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

The 11-year cycle represents a simultaneous parallel change in both the activity level and the total irradiance of the Sun. So, in case of variations of the amplitude of the activity level - a power of a cycle - the amplitude of solar irradiance variations is expected to change correspondingly. The identical correlated course of the long-term variations of activity and luminosity of the Sun on the secular timescale has been observed earlier by Eddy (1976), and Borisenkov (1988). Moreover, according to the data of Borisenkov (1988), in each of 18 deep Maunder-type minima of solar activity, revealed over the span of the last 7500 years, the cooling of climate had been observed, while warming occurred during the periods of high maxima. Thus, the integral radiation has always been essentially higher at the maximum, and it had noticeably decreased at the minima. Therefore, quasi-periodic variations of the solar activity during both the 11-year cycle and 80- and 200-year cycles are accompanied by proportional variations of the integral flux of solar radiation, which result in geophysical effects. The main cause of climate change during the last millennia is the corresponding cyclic variation of the 80- and 200-year component of irradiance correlated with activity. That is why, the contemporary is not anomalous but is ordinary secular global warming (Aguilar 2003; Reid 2000), as well as previous similar cases of warming during the periods of secular activity growth is still mainly connected with an increase of the secular component of solar irradiance variation.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

The coincidence was observed between the places with weak (probably inverse) photospheric longitudinal magnetic fields in the big spot of the AR NOAA 8340 prior to the start of the flare and a common base of the giant arches (loops) and centers of emission visible in the HeI 10830Å line core during the flare. A number of observational facts compel us to make a supposition that the flare was the consequence of an injection of plasma from the places with marked peculiarity of the photospheric magnetic field into the expanding magnetic arcade.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

The East-West asymmetry of sunspot areas has been analyzed on the basis of the Debrecen Photoheliographic Data (DPD). This material provides the opportunity to scrutinize the fine details in the distributions of the East-West differences depending on spot size and central meridional distance during the ascending and the descending phase of 22th cycle.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

Series of H$_\alpha$ spectra and slit-jaw H$_\alpha$ filtergrams of a quiescent prominence (QP) taken at Pic du Midi Observatory on 7 November 1977 are studied. The image processing of the H$_\alpha$ filtergrams reveals an internal structure of the prominence consisting of several arches. Series of high-resolution H$_\alpha$ spectra obtained with the slit located on selected parts of one of the prominence arches chosen for Doppler shift analysis. The prominence arch show cyclic displacement along the line-of-sight (L.O.S.) direction implying Alfven string-mode oscillations.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

In the past 10 years, observations from space have generated a genuine revolution in our understanding of the Sun. Its interior is now “observed” down to a few % of the solar radius, its internal dynamics, its rotation and the large scale flows that are found to exist under its “surface” are studied continuously for over nearly a complete solar cycle. The mechanisms that underlie solar activity are better understood as well as their effects on the heliosphere and on the planets of the Solar System, in particular on the Earth.

However, there are still opened questions that deserve to be answered through a new generation of space instruments, requiring the best experts in the world and an extended fleet of space missions that no single country is able today to undertake alone. In this context, the International Living with a Star programme is a key element that must be pursued with full strength. At the same time, new missions that are not part of that programme should begin to be studied. They will provide the ultimate resolution and accuracy that are necessary to go a step further in the knowledge of the Sun and of its effects on our planet.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

Eclipsing binary light curves have provided the ‘royal road’ (Russell 1948) to fundamental astrophysical information on stars. If radial velocities of the components and a reliable colour/temperature/flux relation are available, parallaxes may be determined and compared with direct measures, e.g. by Hipparcos. Accuracies of existing measures are considered and aspects of the development of this and other methods of distance determination reviewed. Roles for multiwavelength techniques (e.g. VLBA, broad-spectrum photometry) are noted. The recovery of information on new planets orbiting remote stars by transit phenomena will be looked into within this context.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

The CORONAS project is aimed at observation of the Sun in the wide wave-range. The CORONAS-I satellite has been launched to an orbit on 2 March 1994, the CORONAS-F satellite has been launched on 31 July 2001 (see for example Kazachevskaya et al., 1998; Oraevsky et al., 2002). Solar Ultraviolet Radiometer — SUVR provides measurements in the wavelength region $\lambda < 130$ nm and also in the line $L_{\alpha}(\lambda = 121.6)$nm. (Kazachevskaya et al., 1998).To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

With the substantial improvements in observational techniques we have to deal with very big databases, consisting of a few positions of an object over a short time span; this is often not enough to compute a preliminary orbit with traditional tools. In this paper we first review a classical method by C.F. Gauss to compute a preliminary orbit for asteroids. This method, followed by a least squares fit to improve the orbit, still today gives successful results when we have at least three separate observations. Then we introduce the basics of a very recent orbit determination theory, that has been thought just to be used with modern sets of data. These data allow us in many cases to know the angular position and velocity of an asteroid at a given time, even though the radial distance and velocity $(r,\dot r)$, needed to compute its full orbit, are unknown. The variables $(r,\dot r)$ can be constrained to a compact set, that we call the admissible region(AR), whose definition requires that the body belongs to the Solar System, that it is not a satellite of the Earth, and that it is not a “shooting star” (i.e. very close and very small). We provide a mathematical description of the AR: its topological properties are surprisingly simple, in fact it turns out that the AR cannot have more than two connected components. A sampling of the AR can be performed by means of a Delaunay triangulation; a finite number of six-parameter sets of initial conditions are thus defined, with each node of the triangulation representing a possible orbit (a virtual asteroid).To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

RESIK Bragg spectrometer aboard CORONAS-F solar observatory collected spectra of hundreds of solar flares in the unique spectral range between 3.3 Å and 6.1 Å. The instrument's absolute and relative calibrations are now finished which allows for the first time to interpret the observations in terms of the differential emission measure (DEM) distribution. With known DEM shape it is possible to derive and study in detail flaring plasma composition and energy balance. Here we report results of using an improved Maximum Likelihood iterative algorithm (Withbroe-Sylwester) for determination of the DEM distributions for 7 January 2003 flare at 23:30 UT. The study is based on the absolute flux values observed in a number of strong H- and He-like transitions of K xviii, Ar xviii, Ar xvii, S xvi, S xv, Si xiv and Si xiii ions. In this respect, we use line and continuum X-ray emissivities as provided by CHIANTI package from SolarSoft.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

With the advent of the 2004 transit of Venus, interest in historical observations of past transits has been rekindled. We present evidence suggesting that the Maya of the post-classic period actually observed at least one transit of Venus. The frescoes of Mayapan, which are proposed as a record of 12$^{{\rm th}$- or 13$^{{\rm th}}$-century transits, are described and discussed in their astronomical contextTo search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

More than 30 active regions were observed on the Sun during October-November 2003 by SOHO. Approximately half of such regions induced hard X-ray and $\gamma$-ray emission and some solar flares with class M and X were detected during this time by GOES, RHESSI and other experiments. 5 solar flares were detected by AVS-F instrument onboard CORONAS-F satellite. Nuclear $\gamma$-emission lines were detected during some flares observed in this period, in particular, during all flares on October 29 2003.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We report on chromospheric oscillations studied with 15 sec cadence observations obtained at a wavelength of 3.5 mm with the Berkeley-Illinois-Maryland Array (BIMA). Different solar structures, including active and quiet-Sun regions, are analyzed. We compare the high-resolution millimeter 2-D images with Ca II K line images from Big Bear Solar Observatory. Using Fourier and wavelet time series analysis techniques we find signatures of intensity oscillations with periods in the range of 2-7 minutes. We discuss the results in the context of the dynamical model of the solar atmosphere by Carlsson & Stein (1995, 1997).To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

The experimental and theoretic investigation of the halo (a detail of local source structure genetically associated with an active region magnetosphere) is presented by the example of the AR 5200 (October, 1988). Accordingly to the high space resolution observations of RATAN-600 and SSRT the emission of this region was almost completely ($\approx 80$%) consist of halo emission. The peculiarities of the observed halo spectrum and polarization with the model explaining these peculiarities are described. It is shown that the inversion phenomenon for the halo is strongly affected by the propagation conditions influence on the polarized emission inside the large source of this emission. The term ‘self-inversion’ is introduced for this effect. Maximum in the halo spectrum at the wavelengths 5–10 cm is clarified by the scattering and by the strong suppression of the emissivity of non-thermal electrons at these and more longer wavelengths.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

This paper discusses the observations of the 1761 and 1769 transits of Venus by the Dutch-German clergyman Johan Maurits Mohr (1716–1775) from Batavia (Dutch East Indies). We will investigate how Mohr became interested in observing this phenomenon and how he made the necessary preparations. Finally, the fate of his observatory and his instruments will be discussed.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

Some properties of General Magnetic Fields (GMF) of the Sun as a star and of two solar-like stars (an active young $\xi$ Boo A with no cyclicity of activity, and 61 Cyg A – an old star with a moderate level of cyclic activity) are represented.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We present the first center-to-limb G-band images synthesized from high resolution simulations of solar magneto-convection. Towards the limb the simulations show “hilly” granulation with dark bands on the far side, bright granulation walls and striated faculae, similar to observations. At disk center G-band bright points are flanked by dark lanes. The increased brightness in magnetic elements is due to their lower density compared with the surrounding intergranular medium. One thus sees deeper layers where the temperature is higher. At a given geometric height, the magnetic elements are cooler than the surrounding medium. In the G-band, the contrast is further increased by the destruction of CH in the low density magnetic elements. The optical depth unity surface is very corrugated. Bright granules have their continuum optical depth unity 80 km above the mean surface, the magnetic elements 200-300 km below. The horizontal temperature gradient is especially large next to flux concentrations. When viewed at an angle, the deep magnetic elements optical surface is hidden by the granules and the bright points are no longer visible, except where the “magnetic valleys” are aligned with the line of sight. Towards the limb, the low density in the strong magnetic elements causes unit line-of-sight optical depth to occur deeper in the granule walls behind than for rays not going through magnetic elements and variations in the field strength produce a striated appearance in the bright granule walls.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We present results from realistic, high resolution, simulations of solar magneto-convection. Simulations were run with both a mean vertical and a mean horizontal field. The magnetic field is quickly swept out of the granules and meso-granules and concentrated in the intergranular lanes.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html