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1.
Radio waves from the sun were detected 50 years ago, but the microwave detection of other single solar-type stars has remained a challenge. Here, the discovery of four solar-type radio stars is reported. These "solar twin" G stars are radio sources up to 3000 times stronger than the quiet sun. The microwaves most likely originate from a large number of relativistic electrons, possibly produced along with coronal heating, a process that is not understood. Two of the stars are younger than the sun and rotate more rapidly; the dynamo process in the stellar interior is therefore presumably more vigorous, resulting in enhanced coronal activity. One of the detections, however, is an old, metal-deficient G dwarf. 相似文献
2.
The transition of a cylinder of water with a vertical density gradient between convective and viscous spindown occurs near the point at which the maximum buoyancy force equals the radial pressure gradient that is driving the convection. A similar analysis applied to the sun shows the maximum buoyancy force to be 1500 times the convective force. A rapidly rotating solar interior would not be damped by largescale convection. 相似文献
3.
Globally coherent oscillation modes were discovered in the sun about a decade ago, providing a unique seismological probe of the solar interior. Current observations detect modes that are phase-coherent for up to 1 year, with surface velocity amplitudes as low as 2 millimeters per second, and thousands of mode frequencies have been measured to accuracies as high as 1 part in 10(5). This article discusses the properties of these oscillation modes and the ways in which they are adding to our understanding of the structure and dynamics of the sun. 相似文献
4.
Howe R Christensen-Dalsgaard J Hill F Komm RW Larsen RM Schou J Thompson MJ Toomre J 《Science (New York, N.Y.)》2000,287(5462):2456-2460
We have detected changes in the rotation of the sun near the base of its convective envelope, including a prominent variation with a period of 1.3 years at low latitudes. Such helioseismic probing of the deep solar interior has been enabled by nearly continuous observation of its oscillation modes with two complementary experiments. Inversion of the global-mode frequency splittings reveals that the largest temporal changes in the angular velocity Omega are of the order of 6 nanohertz and occur above and below the tachocline that separates the sun's differentially rotating convection zone (outer 30% by radius) from the nearly uniformly rotating deeper radiative interior beneath. Such changes are most pronounced near the equator and at high latitudes and are a substantial fraction of the average 30-nanohertz difference in Omega with radius across the tachocline at the equator. The results indicate variations of rotation close to the presumed site of the solar dynamo, which may generate the 22-year cycles of magnetic activity. 相似文献
5.
Goldstein RM 《Science (New York, N.Y.)》1969,166(3905):598-601
Spectrograms of the radio signals from Pioneer 6 were taken as the spacecraft was occulted by the sun. The spectral bandwidths increased slowly at first, then very rapidly at 1 degree from the sun. In addition, six solar "events" produced marked increases of bandwidth lasting for several hours. The received signal power seemed unaffected by the solar corona. 相似文献
6.
Climatically significant variation of the solar constant (the energy output of the sun) implies measurable change in the solar radius. The available data limit variations of the solar radius between 1850 and 1937 to about 0.25 arc second; modeling of the sun indicates that the solar constant did not vary by more than 0.3 percent during that time. 相似文献
7.
Helioseismology is probing the interior structure and dynamics of the sun with ever-increasing precision, providing a well-calibrated laboratory in which physical processes can be studied under conditions that are unattainable on Earth. Nearly 10 million resonant modes of oscillation are observable in the solar atmosphere, and their frequencies need to be known with great accuracy in order to gauge the sun's interior. The advent of nearly continuous imaged observations from the complementary ground-based Global Oscillation Network Group (GONG) observatories and the space-based Solar and Heliospheric Observatory instruments augurs a new era of discovery. The flow of early results from GONG resolves some issues and raises a number of theoretical questions whose answers are required for understanding how a seemingly ordinary star actually operates. 相似文献
8.
Oscillations of the sun make it possible to probe the inside of a star. The frequencies of the oscillations have already provided measures of the sound speed and the rate of rotation throughout much of the solar interior. These quantities are important for understanding the dynamics of the magnetic cycle and have a bearing on testing general relativity by planetary precession. The oscillation frequencies yield a helium abundance that is consistent with cosmology, but they reinforce the severity of the neutrino problem. They should soon provide an important standard by which to calibrate the theory of stellar evolution. 相似文献
9.
Gloeckler G Galvin AB Ipavich FM Geiss J Balsiger H von Steiger R Fisk LA Ogilvie KW Wilken B 《Science (New York, N.Y.)》1993,261(5117):70-73
Interstellar hydrogen ionized primarily by the solar wind has been detected by the SWICS instrument on the Ulysses spacecraft at a distance of 4.8 astronomical units from the sun. This "pick-up" hydrogen is identified by its distinct velocity distribution function, which drops abruptly at twice the local solar wind speed. From the measured fluxes of pick-up protons and singly charged helium, the number densities of neutral hydrogen and helium in the distant regions of the solar system are estimated to be 0.077 +/- 0.015 and 0.013 +/- 0.003 per cubic centimeter, respectively. 相似文献
10.
High-resolution spectra of nearby stars show absorption lines due to material in the local interstellar cloud. This cloud is deduced to be moving at 26 kilometers per second with respect to the sun, and in the same direction as the "interstellar wind" flowing through the solar system. Measurements by the Ulysses spacecraft show that neutral helium is drifting through the solar system at the same velocity, but neutral hydrogen appears to be moving at only 20 kilometers per second, a result confirmed by new measurements of the hydrogen emission line taken by the High-Resolution Spectrograph on the Hubble Space Telescope. These results indicate that neutral hydrogen atoms from the local interstellar cloud are preferentially decelerated at the heliospheric interface, most likely by charge-exchange with interstellar protons, while neutral helium is unaffected by the plasma. The magnitude of the observed deceleration implies an interstellar plasma density of 0.06 to 0.10 per cubic centimeter, which in turn implies that the heliospheric shock should be less than 100 astronomical units from the sun. 相似文献
11.
为提高太阳能的利用率,以AT89S52单片机为控制核心,采取极轴式跟踪方式,设计了一套以视日运动轨迹跟踪为主、光电跟踪进行跟踪校正的智能型双精度太阳跟踪系统,该系统通过采集时钟芯片信息计算当前太阳位置,实现视日运动轨迹跟踪;同时利用光电传感器采集的光强偏差控制步进电机,实现光电跟踪,校正轨迹偏差,保证聚光板与太阳光相垂直。试验表明,该太阳跟踪系统能在不同天气状况下对太阳进行较准确跟踪,能量接收效率提高20%以上,达到了充分利用太阳能的目的。 相似文献
12.
A brilliant new comet (1979 XI: Howard-Koomen-Michels) was discovered in data from the Naval Research Laboratory's orbiting SOLWIND coronagraph. An extensive sequence of pictures, telemetered from the P78-1 satellite, shows the coma, accompanied by a bright and well-developed tail, passing through the coronagraph's field of view at afew million kilometers from the sun. Preliminary orbital calculations based on the observed motion of the comet's head and morphology of the tail indicate that this previously unreported object is a sungrazing comet and may be one of the group of Kreutz sungrazers. It appears from the data that the perihelion distance was less than 1 solar radius, so that the cometary nucleus encountered dense regions of the sun's atmosphere, was completely vaporized, and did not reappear after the time of closest approach to the sun. After this time, however, cometary debris, scattered into the ambient solar wind, caused a brightening of the corona over one solar hemisphere and to heliocentric distances of 5 to 10 solar radii. 相似文献
13.
Foukal P 《Science (New York, N.Y.)》1994,264(5156):238-239
Recent studies indicate that variation in the sun's luminosity is less than that observed in many other stars of similar magnetic activity. Current findings also indicate that in more active stars, the attenuation by faculae of sunspot luminosity modulation is less effective than in the sun at present. The sun could thus become photometrically more variable (and dimmer) if its magnetic activity exceeded present levels. But the levels of solar activity required for this to occur are not observed in carbon-14 and beryllium-10 records over the past several millennia, which indicates that such an increase in amplitude of surface magnetism-driven variations in solar luminosity is unlikely in the present epoch. 相似文献
14.
Zeilik M 《Science (New York, N.Y.)》1985,228(4705):1311-1313
Evaluation of the Fajada Butte solar marker in Chaco Canyon, New Mexico, on the basis of its ethnographic context and usefulness for confirmatory and anticipatory solar observations indicates that the site does not function as an accurate solar calendar (accurate in the context of the historic Puebloan culture). The site most likely served as a sun shrine rather than as a calendrical observing station. The interpretation of the site as marking the northern declinations of the lunar 18.6-year cycle is not supported by the ethnographic evidence nor can the site be used to anticipate accurately the year of the standstill. 相似文献
15.
R136 (HD 38268) is the central object of the 30 Doradus Nebula, a giant region of ionized hydrogen in the Large Magellanic Cloud. Observations of R136 at low and high spectral resolution with the International Ultraviolet Explorer reveal a peculiar hot object with a massive stellar wind. An outflow speed of 3500 kilometers per second and a temperature of approximately 60,000 K are indicated by the spectra. The bulk of the observed ultraviolet radiation must come from R136a, the brightest and bluest component of R136. Its absolute visual magnitude and observed temperature imply a luminosity about 10(8) times that of the sun. Most of the ionizations produced in 30 Doradus are provided by this peculiar object. If RI36a is a dense cluster of very hot stars, about 30 stars of classes O3 and WN3 exist in a region estimated to have a diameter of less than 0.1 parsec. This is inconsistent with the ultraviolet line spectrum and the evidence for optical variability. An alternative interpretation of the observations is that the radiation from R136a is dominated by a single superluminous object with the following approximate properties: luminosity and temperature as given above, a radius 100 times that of the sun, a mass 2500 times that of the sun, and a loss rate of 10(-3.5) solar masses per year. Model interior calculations for hydrogen-burning stars are consistent with these parameters. Such stars, however, are expected to be unstable, and this may account for the massive stellar wind. 相似文献
16.
Frisch PC 《Science (New York, N.Y.)》1994,265(5177):1423-1427
The first encounter between the sun and the surrounding interstellar cloud appears to have occurred 2000 to 8000 years ago. The sun and cloud space motions are nearly perpendicular, an indication that the sun is skimming the cloud surface. The electron density derived for the surrounding cloud from the carbon component of the anomalous cosmic ray population in the solar system and from the interstellar ratio of Mg(+) to Mg degrees toward Sirius support an equilibrium model for cloud ionization (an electron density of 0.22 to 0.44 per cubic centimeter). The upwind magnetic field direction is nearly parallel to the cloud surface. The relative sun-cloud motion indicates that the solar system has a bow shock. 相似文献
17.
Because of instrumental sensitivity limits and stellar distances, the types of x-ray flares observable on stars have been intrinsically much more energetic than those on the sun. Such enormous events are a useful extrapolation of the solar phenomenon if the underlying assumption is correct that they form a continuous sequence involving similar physical processes as on the sun. The Advanced Satellite for Cosmology and Astrophysics (ASCA), with its greater sensitivity and high-energy response, is now able to test this hypothesis. Direct comparison with solar flares measured by the x-ray-monitoring Geostationary Operational Environmental Satellites (GOES) is possible. The detection of flares on Proxima Centauri that correspond to GOES M-class events on the sun are reported. 相似文献
18.
19.
Ultrathin amorphous coatings on lunar dust grains 总被引：1，自引：0，他引：1
Bibring JP Duraud JP Durrieu L Jouret C Maurette M Meunier R 《Science (New York, N.Y.)》1972,175(4023):753-755
UItrathin amorphous coatings have been observed by high-voltage electron microscopy on micrometer-sized dust grains from the Apollo 11, Apollo 12, Apollo 14, and Luna 16 missions. Calibration experiments show that these coatings result from an "ancient" implantation of solar wind ions in the grains. This phenomenon has interdisciplinary applications concerning the past activity of the sun, the lunar albedo, the ancient lunar atmosphere and magnetic field, the carbon content of lunar soils, and lunar dynamic processes. 相似文献
20.
湖北省太阳能资源时空分布特征及区划研究 总被引：8，自引：0，他引：8
利用武汉、宜昌等7个站点1961~2004年逐年、逐月太阳总辐射与日照百分率资料,采用最小二乘法确定湖北省太阳总辐射计算公式参数,推算出广大无辐射观测地区的逐年、逐月太阳总辐射;结合日照时数、晴天日数、阴天日数等指标,对湖北省太阳能资源的时空分布特征及气候变化趋势进行了分析;以全国太阳能资源区划为基础,制定了湖北省太阳能资源区划指标,开展了湖北省太阳能区划工作。结果表明:湖北太阳能资源北多南少,同纬度相比,平原多,山区少;太阳能资源夏季最丰富,尤其是8月,总辐射、日照时数、晴天日数均为全年最高,湖北东部秋季大气层结稳定,太阳能资源仅次于夏季;冬季虽然晴天较多,但由于太阳直射南半球,夜长昼短,总辐射全年最低。将全省太阳能资源分为3个区,鄂东北7~12月每月有近一半或以上的晴天,为1级可利用区,也是湖北太阳能资源最佳区域;江汉平原、鄂东南、鄂北岗地部分地区等地为2级可利用区,是光电与光生物质能综合利用的最佳区域;鄂西南、长江河谷地区为太阳能贫乏区。 相似文献