共查询到20条相似文献，搜索用时 31 毫秒
1.
V. G. Turyshev 《Astronomy Letters》2009,35(4):215-234
We study the impact of relativistic gravitational deflection of light on the accuracy of future Space Interferometry Mission
(SIM). We estimate the deflection angles caused by the monopole, quadrupole and octupole components of gravitational fields
for a number of celestial bodies in the solar system. We observe that, in many cases, the magnitude of the corresponding effects
is significantly larger than the 1 μas accuracy expected from SIM. This fact argues for the development of a relativistic
observational model for the mission that would account for the influence of both static and time-varying effects of gravity
on light propagation. Results presented here are different from the ones obtained elsewhere by the fact that we specifically
account for the differential nature of the future SIM astrometric measurements. We also obtain an estimate for the accuracy
of possible determination of the Eddington’s parameter γ via SIM global astrometric campaign; we conclude that accuracy of ∼7 × 10−6 is achievable via measurements of deflection of light by solar gravity.
The article was translated by the authors. 相似文献
2.
P. Rudawy K. J. H. Phillips A. Buczylko D. R. Williams F. P. Keenan 《Solar physics》2010,267(2):305-327
Some 8000 images obtained with the Solar Eclipse Coronal Imaging System (SECIS) fast-frame CCD camera instrument located at Lusaka, Zambia, during the total eclipse of 21 June 2001 have been analysed
to search for short-period oscillations in intensity that could be a signature of solar coronal heating mechanisms by MHD
wave dissipation. Images were taken in white-light and Fe xiv green-line (5303 ?) channels over 205 seconds (frame rate 39 s−1), approximately the length of eclipse totality at this location, with a pixel size of four arcseconds square. The data are
of considerably better quality than those that we obtained during the 11 August 1999 total eclipse (Rudawy et al.: Astron. Astrophys. 416, 1179, 2004), in that the images are much better exposed and enhancements in the drive system of the heliostat used gave a much improved
image stability. Classical Fourier and wavelet techniques have been used to analyse the emission at 29 518 locations, of which
10 714 had emission at reasonably high levels, searching for periodic fluctuations with periods in the range 0.1 – 17 seconds
(frequencies 0.06 – 10 Hz). While a number of possible periodicities were apparent in the wavelet analysis, none of the spatially
and time-limited periodicities in the local brightness curves was found to be physically important. This implies that the
pervasive Alfvén wave-like phenomena (Tomczyk et al.: Science
317, 1192, 2007) using polarimetric observations with the Coronal Multi-Channel Polarimeter (CoMP) instrument do not give rise to significant oscillatory intensity fluctuations. 相似文献
3.
《Astroparticle Physics》2010,33(6):286-293
In the past, there have been reports of the observation of decrease in the flux of secondary cosmic γ-rays during a total solar eclipse. We have measured the flux of secondary cosmic γ-rays during the total solar eclipse that occurred at Novosibirsk in Russia, on 1 August 2008. Highly sensitive measurements were carried out by using a detector system with built-in redundancy. The system consisted of two independent, large volume NaI(Tl) scintillator detectors for sensitive and reliable measurements. The data display significant variability in the flux of secondary γ-rays in the energy range 50–4600 keV. Just prior to the total solar eclipse a change ∼9% in the flux was observed, followed by a small but steady decrease ∼4% during the eclipse. The temporal variation in the observed flux of γ-rays were found to be nearly identical for the two detectors. The energy dependence of the variation was further studied by binning the yield in three energy ranges, namely, 100–200, 200–400 and 400–4600 keV. The nearly identical time variation observed in the two independent measurements provides confidence that the measured variation is real and not an artifact of the instrumentation. Systematic observations during the future eclipses are required to study this fascinating phenomenon which is not yet understood. 相似文献
4.
The paper presents results of optical observations and analysis of dynamics of effects on the earth’s lower atmosphere of
the partial solar eclipse (of magnitude 42%) of August 1, 2008, near Kharkov. This is compared with the effects induced by
the partial solar eclipses on August 11, 1999, and October 3, 2005. All three eclipses occurred around midday. The standard
deviation of the solar-limb displacement σ
S
during the eclipses on October 3, 2005, August 1, 2008, and August 11, 1999, was established to decrease by 0.13, 0.30, and
0.68″ at the maximum of the solar obscuration function 0.13, 0.31, and 0.73, respectively, so that the temperature drop in
the earth’s lower atmosphere t
a
was 1.3, 2.0, and 7.3 K. The time lags of decreases of σ
S
and t
a
was found to be 15 and 5 minutes. 相似文献
5.
The radial brightness distribution of the Sun at 3.2 mm is recalculated for the 7 March, 1970 total solar eclipse by an improved method. The results from the first contact of the 30 June, 1973 total eclipse are also analyzed. Limb brightening is apparent for the 1970 eclipse when all four contacts are averaged. The 1973 eclipse indicates strong limb brightening, although the detailed shape differs from the 1970 eclipse. 相似文献
6.
Near second and third contact during a solar eclipse the spatial spectrum of the solar illumination changes as the relative power at high spatial frequencies increases strongly. Since groundlevel atmospheric scintillation depends on a weighted integral of the image power spectrum, we can expect to see a measureable time dependence to solar scintillation during an eclipse. This effect was observed during an annular solar eclipse and quantitatively compared with a scintillation model.Operated by the Association of Universities for Research in Astronomy, Inc. (AURA) under cooperative agreement with the National Science Foundation. 相似文献
7.
We study the effects of a non-singular gravitational potential on satellite orbits by deriving the corresponding time rates
of change of its orbital elements. This is achieved by expanding the non-singular potential into power series up to second
order. This series contains three terms, the first been the Newtonian potential and the other two, here R
1 (first order term) and R
2 (second order term), express deviations of the singular potential from the Newtonian. These deviations from the Newtonian
potential are taken as disturbing potential terms in the Lagrange planetary equations that provide the time rates of change
of the orbital elements of a satellite in a non-singular gravitational field. We split these effects into secular, low and
high frequency components and we evaluate them numerically using the low Earth orbiting mission Gravity Recovery and Climate
Experiment (GRACE). We show that the secular effect of the second-order disturbing term R
2 on the perigee and the mean anomaly are 4″.307×10−9/a, and −2″.533×10−15/a, respectively. These effects are far too small and most likely cannot easily be observed with today’s technology. Numerical
evaluation of the low and high frequency effects of the disturbing term R
2 on low Earth orbiters like GRACE are very small and undetectable by current observational means. 相似文献
8.
Richard Woo 《Solar physics》2007,241(2):251-261
In the absence of magnetic field measurements of the solar corona, the density structure of white-light images has provided
important insight into the coronal magnetic field. Recent work sparked by highly sensitive radio occultation measurements
of path-integrated density has elucidated the density structure of unprocessed solar eclipse pictures. This paper does the
same for processed images that reveal low-contrast small-scale structures, specifically Koutchmy’s edge-enhanced white-light
image of the 11 August 1999 solar eclipse. This processed image provides visual evidence for two important results deduced
from radio occultation measurements of small-scale density variations. First, in addition to the closed loops readily seen
at the base of the corona in high-resolution EUV and soft X-ray images, open filamentary structures permeate the corona including
active regions generally thought to be magnetically closed. Observed at the image resolution, the filamentary structures are
1° wide in latitude and an order of magnitude smaller than polar plumes. Second, although inhomogeneities that are convected
along with the solar wind are also present, filamentary structures dominate the image because of their steeper density gradients.
The quantitative profile of polarized brightness (pB) at the base of the corona shows that the filamentary structures have transverse density gradients that are proportional
to their density. This explains why edge-enhanced images, limited in sensitivity to density gradients, tend to detect filamentary
structures more readily in high-density regions (e.g., active regions, streamer stalks, and prominences) than in low-density polar coronal holes, and why filamentary structures
seem more prevalent in solar eclipse pictures during solar maximum. The pB profile at the base of the corona also fills the gap in Doppler measurements there, reinforcing that open ultra-fine-scale
filamentary structures observed by the radio measurements are predominantly radial and that they are an integral part of the
radial expansion of the solar wind. 相似文献
9.
Thierry Appourchaux Raymond Burston Yanbei Chen Michael Cruise Hansjörg Dittus Bernard Foulon Patrick Gill Laurent Gizon Hugh Klein Sergei Klioner Sergei Kopeikin Hans Krüger Claus Lämmerzahl Alberto Lobo Xinlian Luo Helen Margolis Wei-Tou Ni Antonio Pulido Patón Qiuhe Peng Achim Peters Ernst Rasel Albrecht Rüdiger Étienne Samain Hanns Selig Diana Shaul Timothy Sumner Stephan Theil Pierre Touboul Slava Turyshev Haitao Wang Li Wang Linqing Wen Andreas Wicht Ji Wu Xiaomin Zhang Cheng Zhao 《Experimental Astronomy》2009,23(2):491-527
ASTROD I is a planned interplanetary space mission with multiple goals. The primary aims are: to test general relativity with
an improvement in sensitivity of over three orders of magnitude, improving our understanding of gravity and aiding the development
of a new quantum gravity theory; to measure key solar system parameters with increased accuracy, advancing solar physics and
our knowledge of the solar system; and to measure the time rate of change of the gravitational constant with an order of magnitude
improvement and the anomalous Pioneer acceleration, thereby probing dark matter and dark energy gravitationally. It is an
international project, with major contributions from Europe and China and is envisaged as the first in a series of ASTROD
missions. ASTROD I will consist of one spacecraft carrying a telescope, four lasers, two event timers and a clock. Two-way,
two-wavelength laser pulse ranging will be used between the spacecraft in a solar orbit and deep space laser stations on Earth,
to achieve the ASTROD I goals. A second mission, ASTROD (ASTROD II) is envisaged as a three-spacecraft mission which would
test General Relativity to 1 ppb, enable detection of solar g-modes, measure the solar Lense–Thirring effect to 10 ppm, and
probe gravitational waves at frequencies below the LISA bandwidth. In the third phase (ASTROD III or Super-ASTROD), larger
orbits could be implemented to map the outer solar system and to probe primordial gravitational-waves at frequencies below
the ASTROD II bandwidth.
相似文献
| Wei-Tou NiEmail: |
10.
《New Astronomy》2007,12(7):562-568
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. 相似文献
11.
During the total solar eclipse at Akademgorodok, Siberia, Russia, on 1 August 2008, we imaged the flash spectrum with a slitless
spectrograph. We have spectroscopically determined the duration of totality, the epoch of the second and third contacts and
the duration of the flash spectrum. Here we compare the 2008 flash spectra with those that we similarly obtained from the
total solar eclipse of 29 March 2006, at Kastellorizo, Greece. Any changes of the intensity of the coronal emission lines,
in particularly those of Fe x and Fe xiv, could give us valuable information about the temperature of the corona. The results show that the ionization state of the
corona, as manifested especially by the Fe xiv emission line, was much weaker during the 2008 eclipse, indicating that following the long, inactive period during the solar
minimum, there was a drop in the overall temperature of the solar corona. 相似文献
12.
Plasma and magnetic field parameter variations across fast forward interplanetary shocks are analyzed during the last solar
cycle minimum (1995–1996, 15 shocks), and maximum year 2000 (50 shocks). It was observed that the solar wind velocity and
magnetic field strength variation across the shocks were the parameters better correlated with Dst. Superposed epoch analysis centered on the shock showed that, during solar minimum, B
z
profiles had a southward, long-duration variation superposed with fluctuations, whereas in solar maximum the B
z
profile presented 2 peaks. The first peak occurred 4 hr after the shock, and seems to be associated with the magnetic field
disturbed by the shock in the sheath region. The second peak occurred 19 hr after the shock, and seems to be associated with
the ejecta fields. The difference in shape and peak in solar maximum (Dst peak =−50 nT, moderate activity) and minimum (Dst peak =−30 nT, weak activity) in average Dst profiles after shocks are, probably, a consequence of the energy injection in the magnetosphere being driven by different
interplanetary southward magnetic structures. A statistical distribution of geomagnetic activity levels following interplanetary
shocks was also obtained. It was observed that during solar maximum, 36% of interplanetary shocks were followed by intense
(Dst≤−100 nT) and 28% by moderate (−50≤Dst <−100 nT) geomagnetic activity. During solar minimum, 13% and 33% of the shocks were followed by intense and moderate geomagnetic
activity, respectively. Thus, during solar maximum a higher relative number of interplanetary shocks might be followed by
intense geomagnetic activity than during solar minimum. One can extrapolate, for forecasting goals, that during a whole solar
cycle a shock has a probability of around 50–60% to be followed by intense/moderate geomagnetic activity. 相似文献
13.
Cowsik Ramanath Singh Jagdev Saxena A.K. Srinivasan R. Raveendran A.V. 《Solar physics》1999,188(1):89-98
Encouraged by the detection of high-frequency, low-amplitude continuum intensity oscillations in the solar corona during the total solar eclipse of 1995, we designed and fabricated a six-channel photometer incorporating low-noise Hamamatsu R647 photomultipliers. Fast photometry at five different locations in the solar corona was performed at Don Bosco Mission, Venezuela during the total solar eclipse of 26 February 1998. Three interference filters with passbands of about 150 Å and centered around 4700, 4900, and 5000 Å were used. The photometric data were recorded at a rate of 20 Hz in three channels and 50 Hz in the remaining three channels. The power spectrum analysis of one of the channels that recorded appreciable counts indicates the existence of intensity oscillations in the frequency range 0.01–0.2 Hz. A least-squares analysis yields 90.1, 25.2, and 6.9 s periods for the three prominent components which have amplitudes in the range 0.5–3.5% of the coronal brightness. These periods and their amplitudes are similar to those detected in the coronal intensity oscillations during the 1995 eclipse. 相似文献
14.
15.
K. Saaidi A. Vajdi S. W. Rabiei A. Aghamohammadi H. Sheikhahmadi 《Astrophysics and Space Science》2012,337(2):739-745
We introduce a new approach for investigating the weak field limit of vacuum field equations in f(R) gravity and we find the weak field limit of f(R)=R+μ
4/R gravity. Furthermore, we study the strong gravity regime in R+μ
4/R model of f(R) gravity. We show the existence of strong gravitational field in vacuum for such model. We find out in the limit μ→0, the weak field limit and the strong gravitational field can be regarded as a perturbed Schwarzschild metric. 相似文献
16.
Serge Koutchmy 《Solar physics》1977,51(2):399-407
Radially and tangentially polarized pictures of the solar corona obtained near 4500 Å during the 30 June, 1973 solar total eclipse have been used to derive a model of a trans-polar coronal hole. The hole is identified by using OSO-7 EUV spectroheliograms. The line of sight coincides with the privileged plan of the hole over the N-polar region. A new method of absolute calibration is used. The Saito (1970) method is applied to determine the electron densities. Extrapolated values of densities down to the surface are lower than have ever been observed although derived hydrostatic temperatures are certainly not: N
e
× 107 cm–3 and T = 2 × 106 K. The morphological peculiarities of polar regions are considered.On leave from Institut d'Astrophysique, CNRS, Paris as NRC Research Associate. 相似文献
17.
The focussing of gravitational radiation by the interior and exterior gravitational field of a Newtonian gravitational lens
is considered. A graphical method for determining the caustic structure of a Newtonian gravitational lens is presented and
the caustic structure of a solar type gravitational lens is discussed. Estimates of the amplitude magnification in the caustic
region indicate that waves with frequencies less than a critical cutoff frequency ω
c
are not amplified significantly. For a lens of massM this cutoff frequency is ω
c
≈(10-1πM)-1; for the Sun ω
c
≈104s-1.
Work supported in part by National Science Foundation Grant PHY78-05368. 相似文献
18.
The solar wind quasi-invariant (QI) has been defined by Osherovich, Fainberg, and Stone (Geophys. Res. Lett.
26, 2597, 1999) as the ratio of magnetic energy density and the energy density of the solar wind flow. In the regular solar wind QI is a
rather small number, since the energy of the flow is almost two orders of magnitude greater than the magnetic energy. However,
in magnetic clouds, QI is the order of unity (less than 1) and thus magnetic clouds can be viewed as a great anomaly in comparison
with its value in the background solar wind. We study the duration, extent, and amplitude of this anomaly for two groups of
isolated magnetic clouds: slow clouds (360<v<450 km s−1) and fast clouds (450≤v<720 km s−1). By applying the technique of superposition of epochs to 12 slow and 12 fast clouds from the catalog of Richardson and Cane
(Solar Phys. 264, 189, 2010), we create an average slow cloud and an average fast cloud observed at 1 AU. From our analysis of these average clouds,
we obtain cloud boundaries in both time and space as well as differences in QI amplitude and other parameters characterizing
the solar wind state. Interplanetary magnetic clouds are known to cause major magnetic storms at the Earth, especially those
clouds which travel from the sun to the Earth at high speeds. Characterizing each magnetic cloud by its QI value and extent
may help in understanding the role of those disturbances in producing geomagnetic activity. 相似文献
19.
Mykola I. Pishkalo 《Solar physics》2006,233(2):277-290
We have investigated the correlation between the relative sunspot number and tilt of the heliospheric current sheet (HCS)
in solar cycles 21–23. Strong and highly significant positive correlation (r > 0.8, P < 0.001) was found for corresponding data in the time interval from May 1976 through December 2004. Cross-correlation analysis
does not reveal any time shift between the data sets. Reconstructed values of the HCS tilt, for the time interval before 1976,
are found using sunspot numbers. To take different amplitude of solar cycles into account they were then normalized to zero
in the minima of the solar activity and to average in solar cycles 21–23 maximal calculated HCS tilt in the maxima. These
normalized reconstructed HCS data are compared with the angular positions of the brightest coronal streamers observed during
total solar eclipses in 1870–2002, and their agreement is better for the minima of the solar activity than for the maxima. 相似文献
20.
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. 相似文献