Multi-Wavelength CCD Observations of the 15 November 1999 Mercury Transit

This paper presents the results of a study with images of the Mercury transit of the Sun, 15 November 1999, as observed at the Prairie View Solar Observatory and with three wavelengths of the TRACE satellite. These CCD observations provide an objective source for comparing the optical effects that cause the historic Black Drop under different conditions and with different filters. It appears that a sharp, uniform boundary of sufficient contrast (the solar limb, with the sky beyond the limb being at least as dark as the interior of the Mercurian disk), with a blurring agent, is necessary to produce the effect. Without all these conditions, as in the case of narrow-band Hα at line center or the TRACE UV (1600 Å) and EUV (171 Å), the visibility of the Black Drop is greatly reduced or eliminated, due to the contrast-lowering background of the chromosphere or corona, scattering more light into the umbilicus region.     

TRACE observations of the 15 November 1999 transit of Mercury and the Black Drop effect: considerations for the 2004 transit of Venus

Historically, the visual manifestation of the “Black Drop effect,” the appearance of a band linking the solar limb to the disk of a transiting planet near the point of internal tangency, had limited the accuracy of the determination of the Astronomical Unit and the scale of the Solar System in the 18th and 19th centuries. This problem was misunderstood in the case of Venus during its rare transits due to the presence of its atmosphere. We report on observations of the 15 November 1999 transit of Mercury obtained, without the degrading effects of the Earth's atmosphere, with the Transition Region and Coronal Explorer spacecraft. In spite of the telescope's location beyond the Earth's atmosphere, and the absence of a significant mercurian atmosphere, a faint Black Drop effect was detected. After calibration and removal of, or compensation for, both internal and external systematic effects, the only radially directed brightness anisotropies found resulted from the convolution of the instrumental point-spread function with the solar limb-darkened, back-lit, illumination function. We discuss these effects in light of earlier ground-based observations of transits of Mercury and of Venus (also including the effects of atmospheric “seeing”) to explain the historical basis for the Black Drop effect. The methodologies we outline here for improving upon transit imagery are applicable to ground-based (adaptive optics augmented) and space-based observations of the 8 June 2004 and 5-6 June 2012 transits of Venus, providing a path to achieving high-precision measurements at and near the instants of internal limb tangencies.     

Observations of the sodium tail of Mercury

Cross-sections of the sodium emission tail of Mercury were measured at various distances down the tail when Mercury was moving away from the Sun (true anomaly angles <180°), and again when Mercury was moving towards the Sun (true anomaly angles >180°). As predicted in early modeling studies, significant differences were expected between these two cases, as the result of Doppler shifts to higher solar intensity in the former case, and to lower solar intensity for the latter case. For observations with Mercury moving away from the Sun, the sodium tail was observed out to about 40,000 kilometers (16 Mercury radii, RM) downstream, expanding, on average, at a rate of 1.9±0.3 km/s. The source rates for sodium generation from Mercury into the tail were found to be in the range 2-5×¹⁰²³ atoms/s, corresponding to between 1 and 10% of the estimated total sodium production rate on the planet. The limiting value of radiation acceleration required to produce an observable sodium tail was estimated to be 112±24 cm/s². For observations where Mercury was moving towards the Sun, the emission intensity in the sodium tail decreased very rapidly with distance downstream, disappearing entirely beyond 12,000 (6 RM) kilometers for radiation accelerations of 128.7 and 135.4 cm/s². For smaller radiation accelerations, the sodium tail was not detectable at all, yielding a limiting value for tail generation of about 122±2 cm/s². Interpretation of the limiting radiation acceleration values suggests that the process that generates the sodium tail yields atoms with energies greater than 3 eV. Particle sputtering is the most reasonable source process.     

Video Observations Of Leonids 1999

We analyse data obtained by different ground-based video camera systems during the 1999 Leonid meteor storm. We observe similar activity profiles at nearby observing sites, but significant differences over distances in the order of 4,000 km. The main peak occured at 02:03 UT (λ_⊙=235.286, J2000, corrected for the time of the topocentric stream encounter). At the Iberian peninsula quasi-periodic activity fluctuations with a period of about 7 min were recorded. The camera in Jordan detected a broad plateau of activity at 01:39–01:53 UT, but no periodic variations. The Leonid brightness distribution derived from all cameras shows a lack of faint meteors with a turning point close to +3^m, which corresponds to meteoroids of approximately 10^-3 g. We find a pin-point radiant at αalpha=153.65 ±0.1, δ=21.80 ±0. (λ_⊙=235.290). The radiant positionis identical before and after the storm, and also during the storm no driftis observed. This revised version was published online in July 2006 with corrections to the Cover Date.     

Contour Observations of the Leonid Shower in 1999

Contour visual observations of the Leonid meteor shower were made on December 18, 1999 by the method in which different groups of observers counted meteors in zenith, near the horizon, and observed through binoculars to study the luminosity function and the space density of the swarm. The luminosity function was obtained in the range of magnitudes from –8 ^m to +9 ^m . Over a wide range of magnitudes, the luminosity function is found to be nonlinear and is adequately approximated with a second-order curve. The logarithm of the meteor space density (m) reaches saturation at about 10 ^m , indicating that particles that give rise to meteors fainter than 10 ^m are absent in the swarm. The meteor stream reached its activity peak at a solar longitude of 235°, 287 (2 ^h 05 ^m UT). The peak visual zenithal hourly rate was about 7000 per one observer over an averaging interval of 1 min. The swarm space density increased by a factor of 6 within 0.5 hours and exceeded 600 particles per 10⁹ km³ for meteors brighter than +4 ^m . In the peak night, the luminosity-function exponent demonstrates no regular trend and reflects the intercepting of certain swarm clouds by the Earth.     

Observations of 1970 May 9 Mercury transit

During the 1970 May 9 Mercury transit on the solar disk, the Rome Astronomical Observatory performed various direct and spectroscopic observations of the apparent diameter of the planet, the instant of its third contact, the position angles of egress, and the least distance from the sundisk center. Independent methods were used for diameter determination: photometry, isodensitometry, dark calibrated disks, and photometric observations through a diaphragm closing on the planet's image. The maximum deviation among the different determinations is not larger than 0.37″ of arc; the mean weighted value gives a Mercury diameter at 1 a.u. of 6.74″ with an uncertainty of 3.8%. Also observed was a deformation phenomenon on the solar limb near the third contact: its value is estimated as 2.2″ but is not definitive.     

Observations of supernovae in the period 1997–1999

Astronomy Letters - We present our photometric observations of the 15 supernovae (SN) discovered in the period 1997–1999; of these, six are type Ia SN, two are peculiar type Ia SN, three are...     

Observations of Solar EUV Radiation with the CORONAS-F/SPIRIT and SOHO/EIT Instruments

The SPIRIT complex onboard the CORONAS-F satellite has routinely imaged the Sun in the 171, 175, 195, 284, and 304 Å spectral bands since August 2001. The complex incorporates two telescopes. The Ritchey-Chretien telescope operates in the 171, 195, 284, and 304 Å bands and has an objective similar to that of the SOHO/EIT instrument. The Herschel telescope obtains solar images synchronously in the 175 and 304 Å bands with two multilayer-coated parabolic mirrors. The SPIRIT program includes synoptic observations, studies of the dynamics of various structures on the solar disk and in the corona up to 5 solar radii, and coordinated observations with other spaceborne and ground-based telescopes. In particular, in the period 2002–2003, synoptic observations with the SPIRIT Ritchey-Chretien telescope were coordinated with regular 6-hour SOHO/EIT observations. Since June 2003, when EIT data were temporarily absent (SOHO keyholes), the SPIRIT telescope has performed synoptic observations at a wavelength of 175 A. These data were used by the Solar Influence Data Analysis Center (SIDC) at the Royal Observatory of Belgium for an early space weather forecast. We analyze the photometric and spectral parameters of the SPIRIT and EIT instruments and compare the integrated (over the solar disk) EUV fluxes using solar images obtained with these instruments during the CORONAS-F flight from August 2001 through December 2003.     

Mercury Transit for Stray Light Evaluation: IPM-THEMIS Case

Mercury's transit on the solar disk offers ideal conditions to determine the stray light level of instruments. We present here the results on the stray light level deduced from the observation of the Mercury transit on 2003 May 7th at the secondary focus of the THEMIS telescope with the broad-band and spectral channels of the IPM instrument. The scattered light in the broad-band channel is about 17% and about 25% in the spectral channel. The spread function was deduced for the two channels taking into account the observations on the limb and on Mercury's disk. The goal of this paper is to underline the limits of determining the spread function from limb measurements to correct disk observations. Indeed, we show that if a diaphragm is located in the optical path of scattering surfaces, then the spread function deduced from limb measurements can be underestimated compared to the one required for disk observations. The case is illustrated with the results of the IPM-THEMIS instrument. The spread function deduced from limb measurements is able to correct disk observations in the broad-band channel but not in the spectral channel, even if the two channels are illuminated through the same telescope configuration.     

2004年6月8日金星凌日Hα色球观测

介绍了2004年6月8日云南天文台全日面Hα色球望远镜观测金星凌日的情况，以及对太阳色球活动的监测，并直接给出不同时刻金星在太阳球面的投影和金星的实时图像资料。金星凌日时，Hα色球活动区均未发生耀斑爆发及其它伴随现象。整个凌日过程金星没有掩盖活动区。     

A Cyclone on Mars: Observations in 1999

Observations of a cyclone in the Martian northern hemisphere from April 24 to April 27, 1999, are reported. The cyclone was revealed by the Hubble Space Telescope (HST), but later it was identified in CCD images obtained earlier by the author from April 24 to April 26 with the 0.6-m telescope of the Astrophysical Institute Observatory. The cyclone was situated close to the dawn limb at about 65° north latitude. As in the HST images, the cyclone was seen distinctly only at short (<550 nm) wavelengths. The cyclone drifted in the direction of the Martian rotation. The average drift velocity is estimated to be 19 km/h.     

H α Observations of 8 June, 2004 Venus Transit

The cosmic event of Venus transit across the solar disk occurred on 8 June, 2004. The previous such event was witnessed about 122 years ago on 6 December, 1882. We observed this rare transit in H _α 6563 Å line-center from Udaipur Solar Observatory (USO) using both the full-disk and small field-of-view solar telescopes. In the earlier historical transits, a “black-drop” effect was observed in white light images, during the contact phases. The transit of 8 June, 2004 provided a unique opportunity to observe this effect, for the first time, in H _α. We report that the “black-drop” effect is present in H _α also, as in the white light observations made by the ground-based Global Oscillation Network Group (GONG) instrument and the space-borne Transition Region and Coronal Explorer (TRACE) satellite. We did not observe any noticeable “aureole” (atmospheric glow) around Venus during the ingress or egress phases. We have compared the H _α images with the multi-wavelength data obtained from the TRACE satellite.     

On the Origin of the 1999 Leonid Storm as Deduced from Photographic Observations

Photographic multi-station observations of 18 Leonid meteorsobtained by the Spanish Photographic Meteor Network are presented. For each meteoroidthe radiant position, trajectory data and orbital parameters are discussed and compared totheoretical radiant positions and orbital elements of particles ejected from 55P/Tempel–Tuttle in 1899.We discuss the role of mean velocity imprecision in the dispersion of some orbital parameters,specially the semimajor axis. Finally, by applying the dust trail theory we have adjusted the1999 Leonidstorm orbits to a defined semimajor axis value to test the quality of photographic observations.     

Observations of the infrared FeXIII lines in the solar corona of 12 November, 1966

The purpose of this paper is to report on some intensity measurements of the Fe xiii lines at 10 747 Å and 10 798 Å made during the total eclipse of 12 November, 1966. Infrared spectra were taken of the solar corona at a dispersion of 90 Å per mm, using an RCA image converter and spectrograph aboard the NASA CV 990 aircraft off the coast of southern Brazil. The spectra have been reduced to equivalent width in terms of the coronal continuum and values derived for different points in the corona.The observed equivalent widths of the lines lie in the range 10 to 30 Å for the 10 747 line and 5 to 12 Å for the 10 798 line. The ratio of these equivalent widths is found to vary from 2.3 in the inner corona to 6 at a point 1.36 solar radii from the center of the Sun.The above results are discussed in terms of the excitation mechanisms involved in producing the lines. In particular, the results are compared with the recent theoretical calculations of Chevalier and Lambert, who are the first to include the effects of proton collisions in the excitation of the 3p ^{2 3} P levels of Fexiii. Our observations are consistent with an electron density of 4 × 10⁸ in the inner corona; a value which compares favorably with those derived by other observers from the strength of the K continuum. These are, to our knowledge, the first eclipse observations of the infrared Fe xiii lines which indicate that proton collisions are important in the excitation of the coronal lines. The coronal abundance of iron is estimated from the equivalent width of the 10 747 line, and in common with other observers we find an overabundance as compared to the photospheric abundance by a factor of 10.     

Soft X-Ray and White-Light Coronal Observations of the Post-Flare Arch on 2 November 1991

A giant post-flare arch observed on 2-3 November 1991 was analyzed using the soft X-ray telescope (SXT) on board Yohkoh and the Mark III (MK3) K-coronameter at the High Altitude Observatory/Mauna Loa Solar Observatory. The rising arch was observed in both soft X-ray and K-corona observations. The estimated rising speed from the MK3 observation was approximately 4 km s^-1. A V-shaped depression area was observed on the south side of the giant arch. Change in the K-corona observations was faint while the arch was rising. According to the solar wind observations by the Pioneer Venus Orbiter and the Interplanetary Cometary Explorer, this giant arch event may have been associated with an interplanetary shock.     

The Eruptive Flare of 15 November 1991: Preflare Phenomena

We present and interpret observations of the preflare phase of the eruptive flare of 15 November, 1991 in NOAA AR 6919. New flux emerged in this region, indicated by arch filaments in Hα and increasing vertical flux in vector magnetograms. With increasing frequency before the eruption, transient dark Hα fibrils were observed that crossed Hα bright plage and the magnetic inversion line to extend from the region of flux emergence to the filament, whose eruption was associated with the flare. These crossing fibrils were dynamic, and were often associated with sites of propagating torsional motion. These sites propagated from the region of flux emergence into the filament flux system. We interpret these morphological and dynamic features in terms of relaxation after magnetic reconnection episodes which create longer field lines within the filament flux system, as envisioned in the tether cutting model, and transfer twist to it, as well. Supplementary material to this paper is available in electronic form at http://dx.doi.org/10.1023/A:1005086108043     

Observations of stray-light and sunspot intensities during the Mercury transit of 1970 May 9

In order to test the usual method for correcting sunspot intensity measurements for stray light, we have measured, during the Mercury transit of 1970 May 9, the intensities of Mercury, a sunspot umbra, and the aureole. The direct observations result in Mercury intensities < 0.06 I and aureole intensities <0.01 I . The stray light correction to the spot intensities has been <(0.03 ± 0.01) I . The main contribution to the stray light on the solar disc is shown to be produced by a spread-function with a half width of 10 arc sec. Consequently, for stray light corrections the range R R + + 20 in the aureole has to be measured very precisely; furthermore, a remarkable fraction of the stray light in the center of an umbra originates from the surrounding penumbra.Mitteilungen aus dem Fraunhofer Institut, Nr. 102.     

Transits of Mercury: Results of Belgrade Observations in 1970 and 1973

Photographic observations of the transits of Mercury over the solar disk in 1970 and 1973 at the Belgrade Observatory were used not only in order to determine the classical parameters, as the times of contacts and least distances to determine the apparent radii of the Sun and Mercury. The mean value of the Sun's semi-diameter reduced to the distance unit differs from AUWERS value by about 1.3 while the Mercury's radius is in good agreement with LE VERRIER 's value. On the basis of quite homogenous observational material and precise observing data it was possible to derive the parallax of the Sun by means of the angular distance changes due to the parallactic effect in the course of transit. The values are determined as: 8.800 ± 0.008 (1970) and 8.788 ± 0.032 (1973). The mean value resulting from the two transits is πs = 8.794 ± 0.013, an amount in striking agreement with that currently used.     

恒星形成区GGD12-15的近红外观测

给出恒星形成区GGD12-15的宽波段JHK和窄波段H2v=1-0S(1)近红外成像观测．观测图像揭示了致密的年轻红外星团和与红外源成协的红外星云，并发现了以H2发射结表征的星团外流活动．大多数红外点源在光学波段不可见；对76颗红外点源的JHK′测光结果显示，有32颗具有红外超，其中5颗表现原恒星特征，表明分子云中的恒星形成活动很活跃．以B8光谱型作为大质量星分界，由色星等图估计出大质量星所占星团比例为-10％～26％．GGD12—15星团的K′星等分布的峰值位于15.0mag，并在13．0mag-16．0mag平坦分布；[H—K′]色分布的峰值出现在-0．7mag，在此以上更红的星团成分占70％．在GGD12-15区新发现的氢分子发射结集中在星团中心领域，其空间分布明显与剧烈的恒星形成活动相关；有5个发射结位于分子外流的中心区域，暗示其激发可能与分子外流同源．     

Precise Determination of the Coordinate Systems for the Yohkoh Telescopes and the Application of a Transit of Mercury

The Yohkoh solar X-ray observatory carries two telescopes that require coalignment at a level better than the minimum pixel size of 2_45. This coalignment is needed both internally within Yohkoh and for many scientific applications involving data from ground-based radio and optical observatories. We describe the methods successfully developed for this purpose and now incorporated in the Yohkoh software. Soft X-ray observations of the 1993 transit of Mercury across the solar disk provided key information for the calibration of the coalignment procedures.