There are many reasons to study the Sun: it is of great scientific interest in its own right; it has profound influences on the Earth; and it is of crucial importance for astronomy, since it is the only star where we can observe fundamental cosmic processes in great detail. However, many of the basic properties of the Sun are still a mystery and so the Sun is one of the liveliest branches of astronomy to which many students are currently being attracted.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

The measurements of the Doppler effect of the photosphere showed the presence of the persistent periodicity 159.9655(5) min. It is interpreted as by-product of the fast-rotating central solar core.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

The atmosphere of Venus was discovered for the first time by the Russian scientist Mikhail V. Lomonosov at the St Petersburg Observatory in 1761. Lomonosov detected the refraction of solar rays while observing the transit of the planet across the disk of the Sun. From these observations he correctly inferred that only the presence of refraction in a sufficiently thick atmosphere could explain the appearance of a light (‘fire’) ring around the night disk of Venus during the initial phase of transit, on the side opposite from the direction of motion. Lomonosov described this phenomenon, which carries his name, as the appearance ‘of a hair-thin luminescence’, which encircled a portion of the planet's disk that had not yet contacted the solar disk. He also observed a bulge set up at the edge of the Sun during the egress phase of the Venus transit. ‘This bears witness to nothing less than the refraction of solar rays in the Venusian atmosphere’, he wrote. This paper is based on the original Lomonosov publications and describes historical approaches to the study involving procedure, drawings, and implications.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

Fundamental information about the nature of solar filaments and governing physical processes are retained in their small-scale structure and dynamics. The paper reviews some recent high resolution studies of filaments, with emphasize on potential impact on current understanding of their physical nature.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

At high spatial and temporal resolution, coronal loops are observed to have a highly dynamic nature. Recent observations with SOHO and TRACE frequently show localized brightening “raining” down towards the solar surface. What is the origin of these features? Here we present for the first time a comparison of observed intensity enhancements from an EIT shutterless campaign with non–equilibrium ionization simulations of coronal loops in order to reveal the physical processes governing fast flows and localized brightening. We show that catastrophic cooling around the loop apex as a consequence of footpoint–concentrated heating offers a simple explanation for these observations. An advantage of this model is that no external driving mechanism is necessary as the dynamics result entirely from the non-linear character of the system.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We present the long term variation of solar corona based on SOHO/EIT observations from 1996 to 2004. EIT provides diagnostics of bulk corona in three channels with overlapping temperature range from 0.5 MK to 2.7 MK and with high spatial resolution. We find that the coronal emission measure increases by a factor of 4 from $2.0\times10^{27}$ cm$^{-5}$ at the solar minimum to $8.0\times10^{27}$ cm$^{-5}$ at the solar maximum. In the meantime, the overall temperature of the corona increases from 1.3 MK to 1.7 MKTo search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

Recent results of two observation campaigns (October 2002 and October 2003) are presented with the objective of understanding the onset of flares and CMEs. The magnetic field was observed with THEMIS and MDI, the chromosphere with the MSDP operating on the German telescope VTT and on THEMIS, the EUV images with SOHO/CDS and TRACE, the X-ray with RHESSI. We show how important is the magnetic configuration of the active region to produce CMEs using two examples: the October 28 2003 X 17 flare and the October 22 2002 M 1.1 flare. The X 17 flare gave a halo CME while the M 1.1 flare has no corresponding CME. The magnetic topology analysis of the active regions is processed with a linear-force-free field configuration.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

As based on analysis of radio maps at the wavelength of 1.76 cm obtained from observations at the radio heliograph Nobeyama the parameters of oscillation processes in solar active regions were studied. As a technique for data processing wavelet analysis was used. The inherent periodicity in oscillations submits the existence of a resonance structure for some kinds of MHD waves in the plasma of the solar atmosphere.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

Results of the new observations of long existing microbursts (MB) are presented. It is revealed that the MB spectrum can have the details with the narrow frequency band $(\Delta f/f <0.03)$. It was earlier marked [Bogod, Mercier & Yasnov (2001)] that the MB arise together with noise storms. In the given observations is detected that MB may be connected with a flare and have arisen about 1.5 hours prior to a flare. For the first time it was possible to register MB, which degree of polarization is less 1 (from 0 till 0.16).To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

Gaia is an all-sky, high precision astrometric and photometric satellite of the European Space Agency (ESA) due for launch in 2010. Its primary mission is to study the composition, formation and evolution of our Galaxy. Over the course of its five-year mission, Gaia will measure parallaxes and proper motions of every object in the sky brighter than visual magnitude 20, amounting to a billion stars, galaxies, quasars and solar system objects. It will achieve an astrometric accuracy of 10 $\mu$as at $V=15$ – corresponding to a distance accuracy of 1% at 1 kpc – and 200 $\mu$as at $V=20$. With Gaia, tens of millions of stars will have their distances measured to a few percent or better. This is an improvement over Hipparcos by several orders of magnitude in the number of objects, accuracy and limiting magnitude. Gaia will also be equipped with a radial velocity spectrograph, thus providing six-dimensional phase space information for sources brighter than $V$$\sim$ 17. To characterize the objects (which are detected in real time, thus dispensing with the need for an input catalogue), each object is observed in 15 medium and broad photometric bands with an onboard CCD camera. With these capabilities, Gaia will make significant advances in a wide range of astrophysical topics. In addition to producing a detailed kinematical map of stellar populations across our Galaxy, Gaia will also study stellar structure and evolution, discover and characterise thousands of exoplanetary systems (extending down to about ten Earth masses for the nearest systems) and make accurate tests of General Relativity on large scales, to mention just some areas. I give an overview of the mission, its operating principles and its expected scientific contributions. For the latter I provide a quick look in five areas on increasing scale size in the universe: the solar system, exosolar planets, stellar clusters and associations, Galactic structure and extragalactic astronomy.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

The December 1639 transit of Venus was only seen and recorded in Much Hoole and Salford, Lancashire, England. It was visible, however, from all over Italy, France, Spain and Portugal. But no one was looking. This paper suggests reasons why.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

The 1N/M7.6 flare of 24 October 2003 at S19E72 were well observed by RHESSI, TRACE, NORH, and the Spectrograph at the Purple Mountain Observatory. After analyzing all the data collected, we established a scenario of the flare and compared it with the standard cartoon of solar flares (e.g., Dennis 1988).To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We describe our experiences with on-orbit calibration of, and scientific observations with, the Fine Guidance Sensors (FGS), white-light interferometers aboard Hubble Space Telescope. Our original goal, 1 milliarcsecond precision parallaxes, has been exceeded on average by a factor of three, despite a mechanically noisy on-orbit environment, the necessary self-calibration of the FGS, and significant temporal changes in our instruments. To obtain accurate absolute parallaxes from these small fields of view ($3^\prime \times 15^\prime$) observations requires a significant amount of ancillary reference star information. These data also permit an independent estimate of interstellar absorption, critical in determining target absolute magnitudes, M$_V$, often the key result of a parallax program. With these techniques we and our collaborators have obtained absolute parallaxes for 21 astrophysically interesting objects. We briefly discuss a recent determination of the parallax of the Pleiades. HST routinely produces parallaxes with half the error of the best Hipparcos results, a precision that continues down to target $V = 15$. The FGS will remain a competitive astrometric tool for the generation of high-precision parallaxes until the advent of longer-baseline space-based interferometers (SIM), or the failure of some key HST component.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

Mutual event observations started in the early 1970s with the Galilean satellites. These observations were needed because of the Voyager spacecraft future arrival. Since 1979, IMCCE has organized observational campaigns for the Galilean satellites (called PHEMU), and since 1995 for the Saturnian satellites (also called PHESAT). Meanwhile, the reduction techniques have been greatly improved. Mutual event observations are one of the most accurate methods for obtaining positions of natural satellites, useful for detecting tidal effects. Hence mutual events of Jovian and Saturnian natural satellites are regularly observed around the world. This paper aims to describe mutual events and the advantages of this kind of observation besides the classical astrometric ones.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

Traditionally the $\alpha - \omega$-dynamo is regarded as a basic theory of solar activity (SA) cycle. Here the model of solar magnetic cycle based on the new MHD-solutions for the mean large-scale magnetic field is presented. The hypothesis of gyrotropic plasma turbulence and cyclic restoring of the poloidal magnetic field from the rising toroidal magnetic flux tubes due to the $\alpha$-effect is not used (see Solov'ev and Kiritchek (2004)).To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

From long-term multicolour photometric observations of strongly spotted stars, one concludes usually on a presence of active longitudes. We argue the latitudinal effects in distribution spots over the surface and noticeable equatorward drift of the low-latitude boundary of the spotted region during the rising phase of activity.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

An account is given of Lord Lindsay's lavishly equipped independent expedition to the Island of Mauritius in the Indian Ocean to observe the 1874 Transit of Venus. The expedition's secondary programme, the deriving of the solar parallax from observations of the minor planet Juno, is also described. This work proved a positive outcome of a generally disappointing event and brought about an important shift in the approach to the parallax challenge. The site on Mauritius where Lord Lindsay observed the Transit in 1874, now preserved as a National Monument, was the centre of celebrations during the Transit of 2004.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

The new model of coronal loop in the form of the double magnetic flux tube embedded into the uniform external magnetic field is proposed to explain the coronal oscillations phenomena. We investigate the MHD-waves in the magnetic flux tube, wich consists of the dense hot cylindrical cord surrounded by the co-axial shell. The magnitudes of Alfven and sound speeds in the cord, in the shell and in the environment are $V_{Ai}$, $C_{si}$, $V_{Am}$, $C_{sm}$, $V_{Ae}$, $C_{se}$ correspondingly. Under the coronal conditions we have \[ C_{se}<C_{si}< V_{Ai}<V_{Ae},\\ C_{si}< V_{Am},\ C_{se}<C_{sm}<V_{Am},\\ C_{sm}<V_{Ai}.\]To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We have digitized and processed the daily K-CaII-line full disk spectroheliograms from the archive of the Kodaikanal Observatory during 1907-1995. The programm has been worked out to determine the boundaries of the bright areas (plages, decayed plages, enhanced network features, K-CaII bright points and so on) with contrast that exceeded a level of the quiet Sun on the given value. About the $1.2\,{\times}\,10^6$ K-CaII active regions of different scales were processed. The coordinates, areas, the tilt and latitude-time distributions of bright features were determined. At the high latitudes the K-CaII bright points form a polar branch of solar activity at the period between the polar magnetic field reversals. This polar activity shows both 11-year's and 22-year's cycles. We found that the polar K-CaII bright point cycles proceed on average 5.5 years the sunspot cycles.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

Figure 1 shows the horizontal velocity pattern of photospheric features in the main part of active region NOAA 9077 on 2000 July 12 – 15, where the horizontal velocity vectors are overlapped by white light images (left) and contours represent $G=-2{\bf U}\cdot {\bf A_p}B_n$ (injective rate of magnetic helicity) inferred from the horizontal velocity vectors and longitudinal magnetic field (right). The black (white) contours with white (black) areas mark the positive (negative) change rate of magnetic helicity of $\pm$5, 20, 50, 100, 180, 300 ($\times 10^{13}G^2m^2s^{-1}$). The arrows overlapped by $G$ mark the transverse magnetic field.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html