The change in the measured position due to the chromatic effect in the optical system is usually so small that it can be neglected. However, in the case of the Hipparcos mission, this effect is of the same magnitude as the targeted precision; it is therefore mandatory to correct for it. The different assumptions adopted to build up such corrections in the Hipparcos framework are presented. Some of their limitations and how they can be overcome to improve the results even today are described. The chromaticity mainly affects red stars and has its strongest impact on the astrometry of very red and highly variable stars such as Miras. Nevertheless, the implications on distance scale determination are rather small.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We report on detection of coronal streamer trace on the night sky over the horizon.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

The Events of energetic particles from solar X-ray flares and shock waves have been studied. The data were taken from the National Geophysical data center (NGDC) in Boulder, Colorado, USA, Where the data were taken during the solar cycle 23rd. The 23rd cycle is the present one, that started in April 1996, and its maximum was in May 2001, and it will be decayed during year 2007. Power spectrum methods have been applied for analysis of the data given, to find the short and intermediate periodicities. The periodicity around 14 days has appeared in this analysis. This has important implications for understanding and predicting the effects of solar activity on the Earth and on the earth's atmosphere. If a Coronal Mass Ejections (CMEs) hit the Earth, it can excite a geomagnetic storm. Large geomagnetic storms, among other things, can cause electrical power which can damage satellite communications. In space CME typically drive shock waves that produce energetic particles that can damage both electronic equipment and astronauts that are outside the protection of the Earth's magnetic field. So, the prediction of the high energetic particle events is of vital importance for space navigation and airline disasters.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

During the second half of the nineteenth century Brazilian astronomers participated in the observations of transit of Venus. In 1874 a Brazilian astronomer, Francisco Antônio de Almeida was sent by the Imperial Observatory to Nagasaki to use the “photographic revolver” invented by Jules Janssen. In 1882 three missions were sent by the Imperial Observatory (Brazil) to observe the transit in St Thomas (Antilles), Punta Arenas (Chile) and Olinda (Brazil). The value of the solar parallax obtained by the Brazilian Commission, led by Luís Cruls, was 8.$\rlap ^{\prime\prime}$808, representing at that time one of the most precise values.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

The cause of 92 geomagnetic disturbances in the period of 1997 – 2003 was analyzed. There were used data from LASCO C3 instrument from SOHO satellite, SOHO LASCO CME Catatalog, and the daily average indices Ap. In this contribution we proposed to search sources of the geomagnetic storms taking into account the old idea by Newkirk and Bohlin (1965). According to this idea a solar coronal streamer can cause geomagnetic disturbance when it crosses the Earth's space.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

Coronal mass ejections (CMEs) are accompanied by several other active phenomena. However, neither their interrelation, nor CMEs' trigger mechanisms have not yet been adequately understood.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

A white-light flare on 2001 March 10 was well observed in the H$\alpha$ line and Ca II$\lambda$8542 line using the imaging spectrograph installed in the Solar Tower Telescope of Nanjing University. Three small sunspots appeared in the infrared continuum image, one of which showed that the infrared continuum is enhanced by 4%-6% compared to the preflare value and it almost disappeared in the continuum image for about 3 min. Near the sunspot, there appeared a hard X-ray (HXR) source, the flux of which showed a good time correlation with the profile of the continuum emission. We propose that electron precipitation followed by radiative backwarming may play the chief role in heating the sunspot.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

Three approaches for coronal magnetic loops on the Sun and the stars are considered: (i) loop as MHD-resonator, (ii) loop as electric circuit, (iii) loop as a magnetic mirror trap.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We investigated variations of the radio emission of the whole Sun at 1.76 cm obtained and archived at the Nobeyama radio heliograph in 1992–2003. For this purpose the daily data of the intensity and also right/left circular polarization of the radio emission with one-second average were processed. It was found that 3 minutes oscillations are present at the different phases of solar activity, including the minimum of activity. Especially conspicuous these oscillations present in a difference between the right and the left circular polarization. Intensity of the oscillations changes with a level of the solar activity. As we register fluctuations from the full Sun that their source can be not only sunspots but also and chromosphere of the Sun. Spectral analysis of the presence of 3-minute oscillations in polarization of the solar radio emission shows that there exist modulation with the periods of 27 and 157 days.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

The phenomena ($\sim 15$ cases) observed with Siberian Solar Radio Telescope (SSRT) in 2003–2004 years are under investigations. These phenomena are identified with CMEs by LASCO and with the associated active regions (ARs). The structure of low corona above these ARs is studied using the observations with RATAN–600. The aim of this cooperative investigation is to follow this phenomenon at the earliest stage when it is developing in low corona.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

This paper reviews some recent results obtained from multi-wavelength studies that extend from white light to radio. Special emphasis is given to radio observations, which can be used to determine emission mechanisms and to trace electron propagation paths and plasma motions. Multi-wavelength comparisons have been found to be essential when analysing flare- and CME-related eruptions, but significant results have also been obtained in ‘quiet’ Sun studies.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

In our contribution we introduce the new Interferometric BIdimensional Spectrometer (IBIS) and present the first results on bisector velocities of two dimensional spectral scans in FeI 7090.4 Å comparing granules and intergranular regions.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

The description of two major flares detected by SONG spectrometer on board the CORONAS-F mission during famous period of solar activity in October- November 2003 and their comparison with soft X-ray measured by GOES-12 is given.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We investigate the line-of-sight velocity oscillations in the sunspot NOAA 0051 during it's disk transit. A favorable concourse of circumstances (observational method, excellent seeing plus intrinsic processes in the sunspot) allowed us to observe in some instances a clear picture of waves propagating in the umbra chromosphere (chevron structure in figure 1). Thus it was possible to measure directly their phase velocity in the immediate region of sunspot umbra. These waves have a period of 2.8 min and propagate from the sunspot center outward with the phase velocity of 45–60 km s$^{-1}$ with the line-of-sight velocity amplitude of about 2 km s$^{-1}$ (figure 2, 3). The waves terminate rather abruptly on the umbra boundary and show no direct linkage with (RPW) running penumbral waves (Zirin and Stein 1972). We pointed out that in our observations the picture of propagation of the waves from the sunspot center in two opposite directions is not accompanied by the propagation of H$\alpha$ umbral flashes in these same directions. Our investigations showed that three-minute oscillations are very poorly pronounced in H$\alpha$ intensity, and no “chevron” structure is present. The spatial coherence of the waves at the umbra center is no more than 2$^{\prime\prime}$. No phase delay was found between line-of-sight velocity signals measured in H$\alpha \pm$0.2 Å and H$\alpha \pm$0.7 Å for a single spatial element. This would imply that the vertical extent of the source is comparable to the observed height scale (1000–1500 km). At the photospheric level there are clearly pronounced periodic motions (T $\sim$5 min) propagating from the umbra and from the superpenumbra to the lines of maximum Evershed velocity. One gets the impression that in some portions the Evershed flow itself is pulsating (Kobanov 2000; Rimmele 1995). Balthasar and Wiehr (1990) developed the idea that the Evershed flows may be a result of superposition of some penumbral structure affected by the underlying oscillating layers. Numerical simulations of wave propagation in a stratified magneto-atmosphere presented by Bogdan et al. (2003) show that the coupling between the fast and slow magneto-acoustic-gravity waves is confined to thin atmospheric layers where the sound speed and the Alfen velocity are comparable in magnitude. Their coherent superposition presents a large variety of Doppler and intensity time series. Interesting, some of their pictures resemble our “chevrons”.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We computed chromospheric models of the Sun as a star and of nine solar analogues. The stars have a wide variety of magnetic activity levels, which allows us to study the differences in atmospheric structures induced by activity.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

The time series of geophysical data are chaotic and, on the other hand, extremely noisy. Thus, though there are a number of advanced methods of chaotic time series prediction, the improvement of geophysical data is crucial to succeed. Mainly, it is connected with low determinism of such time series. The improvement procedure, we are about to represent, does not directly enhance deterministic component, but regularity properties of a signal, and, therefore, causes the increase of a deterministic portion in data. The main advantage consists in the fact that the method preserves the initial structure (information) of a time series, while effectively reduces noises, even knowing nothing about its actual nature.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

Analysis of time series of the solar magnetic field energy (SMFE) at various solar latitudes ($\varphi = -75^{\circ}\div +75^{\circ}$) has been done. Higuchi's technique Higuchi(1988) to measure the fractal dimension (FD) of time series has been chosen and the daily values $B(\varphi,t)$ of the solar magnetic field on the source surface for 1960-1999 have been used. These values had been computed in IZMIRAN using method by Obridko et al. (1994) As a matter of fact, Higuchi's measurements of the FD of time series $X_t$ comes to calculation of the length of the curve $l(k)\sim<\mid X_{t+k}-X_t\mid >k^{-2}$ and estimate of the coefficient $D$ in equation $\lg {l(k)}=A-D\lg k$ for considered range of $k$. The dimensions $D(\varphi,K)$ of the time series $B(\varphi,t)^2$ have been computed for various time scales $0<k<K$ $([k]=[t]=1^d)$. It has been found that at $k>10-27$ the time series of SMFE form fractal with $D\approx1.9$.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

The first observations containing evidence of a measurable stellar parallax were made by Thomas Henderson at the Cape of Good Hope in 1832/33. Although his response to Manuel Johnson's discovery in early 1833, that $\alpha$ Cen has a large proper motion, was to intensify observations for his remaining month at the Cape, Henderson apparently saw no urgency to reduce his observations. Instead he laboured through more routine matters, producing a catalogue of declinations of southern stars, improvements of refraction tables, and work on the solar and lunar parallaxes. It was Bessel's announcement of a determination of the parallax of 61 Cyg that finally stirred Henderson into action in late 1838.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

For multi-wavelength investigations of solar activity it may be used the intensity of cosmic ray, registered by means of neutron monitors, because the variations of cosmic ray intensity are very sensitive for local and global solar activity changes. It is important also for space weather investigation. So, we use special indices characterized the level of cosmic ray activity and some peculiarities of the space weather (Belov et al. 1999). To apply the approach, already used for cosmic ray activity calculation, to the single detector data, we have to study daily run of the counting rate. During quiet days we have in the neutron monitor data sinuslike daily variation. The characteristics of the normal for the current period anisotropy and location of the station define it. Thus, on Alma-Ata station counting rate mainly increases on the first half of day and decreases on the second one. The density changing and the anomalous anisotropy behavior lead to distortion of daily run, and the greater is of cosmic ray disturbance, the more is distortion.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

On the basis of an analogy between solar and stellar flares the optical oscillations with periods of tens of seconds observed on the EV Lac are analyzed. In terms of the diagnostic tool proposed by Zaitsev & Stepanov (1982) the main parameters of the flare loop was obtained. We concluded that source of the optical radiation is located at the loop footpoints and its pulsations are determined by the modulation of the flux of energetic particles.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html