DOCSLIB.ORG

Kp- INDEX and LOCAL HIGH-LATITUDINAL GEOMAGNETIC ACTIVITY

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Kp- INDEX and LOCAL HIGH-LATITUDINAL GEOMAGNETIC ACTIVITY Proceedings of the 9th Intl Conf. “Problems of Geocosmos” (Oct 8-12, 2012, St. Petersburg, Russia) Kp- INDEX AND LOCAL HIGH-LATITUDINAL GEOMAGNETIC ACTIVITY A.E. Levitin, L.I. Gromova, S.V. Gromov, L.A. Dremukhina Pushkov Institute of Terrestrial Magnetism, Ionosphere and Radio Wave Propagation , Troitsk, 142090, Russia, e-mail : [email protected] Abstract. Nowadays the geomagnetic activity seasonal variations are described using monthly data of the global Kp index averaged for several years. As is known, the peak area of the geomagnetic activity seasonal variations corresponds to the equinox periods (maximums), while the two minimums are found at the solstices. It is supposed that the formation of activity areas in the solar regions between 10° and 30° of the N and S geliographical latitudes plays the major role in the equinoctial asymmetry of the geomagnetic activity occurrence. During an equinox the plane of the solar equator coincides with that of the Earth, and in this period the Earth is most vulnerable to the impact of the solar activity areas. We establish the correlation of the ground based magnetometer measurements used to derive Kp index and the data of the high latitude observatories used for AE-index calculating during magnetic storms. We consider inconsistent calculations on the base of Kp index, as far as it doesn’t describe the global geomagnetic activity during magnetic storms, but it describes local high latitude magnetic disturbances in these periods when the polar oval shifts equatorwards and Kp-observatories indicate the increase of the auroral current system intensity. Magnetic storms have the maximum of occurrence near vernal and autumnal equinoxes, and it induces the peaks of the monthly Kp index in March-April and October-November. As we suppose, it would be more accurate to estimate the geomagnetic activity using the data of the magnetic observatories located at the different latitudes of the Northern hemisphere from the equator to the polar cap. For data processing and calculating of the geomagnetic activity we apply a new technology that allows to give quantitative assessment of the current local geomagnetic activity and of the magnetic storm intensity. Introduction Indices of geomagnetic activity K, Kp, AE(AU, AL), Dst were introduced over half a century ago. They reflected the prevailing pre-satellite era view about generation of the external magnetic field activity. To examine geomagnetic variations researchres was able to use observatory geomagnetic data only, and magnetic measurements was stored on photo paper and magnetic tape. They did not know much about interaction of the Earth’ magnetosphere with interplanetary space, physical processes of generation of magnetospheic storms and substorms, processes in the magnetospheric tail. Kp was introduced as a index of geomagnetic activity by Bartels in 1938. Kp scale has the values 0 to 9. The values 0 - 3 are in accord with the quiet state of geomagnetic activity, 4 is in accord with disturbed ones, and 5 - 9 correspond to magnetic storms of different intensity that is described by Dst-index. Global (planetary) three-hour-range index Kp is the mean standardized K-index from 13 subauroral Kp-observatories. By applying the conversion tables, K- indices (and Kp-index correspondingly) are determined from geomagnetic data of Kp-observatories by the special service in GeoForschungsZentrum (GFZ), Potsdam, Germany (http://www-app3.gfz- potsdam.de/kp_index/). In [Yanovsky, 1953].one can find the next description of geomagnetic activity ‘Value characterizing geomagnetic field variation during some time interval by level of its disturbance is called magnetic activity or magnetic disturbance’. Namely, if the geomagnetic field of high amplitude doesn’t change dramatically during any time period geomagnetic activity is described as zero one. Most surprising for quantitative assessment of geomagnetic activity is that we realize geomagnetic activity indices shortcomings which doesn’t allow to describe realistic temporal geomagnetic situation but we continue to use them. Below we discuss these shortcomings of Kp-index and propose new technology to quantitatively e assess geomagnetic activity. Shortcomings of Kp-index of planetary geomagnetic activity Kp-index is used for in the study of magnetism to describe planetary geomagnetic activity. Global three-hour-range index Kp is the mean standardized K-index from 13 subauroral Kp-observatories. The K-index quantifies disturbances in the horizontal component of earth's magnetic field with an integer in the range 0-9 with 1 indicating quiet state of the geomagnetic field and 5 or more indicating a geomagnetic storm. It is derived from the maximum fluctuations of horizontal components observed on a magnetometer during a three-hour interval. 295 Proceedings of the 9th Intl Conf. “Problems of Geocosmos” (Oct 8-12, 2012, St. Petersburg, Russia) The conversion from maximum fluctuation in nT to K-index varies from observatory to observatory (see Table 1).Observatories at higher geomagnetic latitudes routinely experience wider magnetic field fluctuations than lower-latitudes observatories therefore, the magnetic field amplitude range corresponding to K-index =9 at these higher latitudes is wider. A table of conversion assigned to each observatory giving the limits, or range, corresponding to each of the ten values of K. Table 1.Amplitude of horizontal component of Earth's magnetic field assigned corresponding to К = 9 in depending on geomagnetic latitude Ф Ф 64° - 90° 65° - 80° 60° - 65° 55° - 60° 48° - 54° 30° - 47° 0° - 30° H, nT 2500 2000 1000 - 1800 600 - 1500 550 350 300 Observatories at higher geomagnetic latitudes routinely experience wider magnetic field fluctuations than lower-latitudes observatories therefore, the magnetic field amplitude range corresponding to K =9 at these higher latitudes is wider. A table of conversion assigned to each observatory giving the limits, or range, corresponding to each of the ten values of K. But this conversion tables don’t depend on season of the year. The Kp-index is derived from a number of magnetometer stations at mid-latitudes. When the stations are not greatly influenced by the auroral electrojet currents, conditions are termed magnetically quiet. If the auroral zone expands equatorward, however, these stations can record the effects of the auroral electrojet current system and of the magnetospheric ring current and field-aligned currents that can connect it to the ionosphere. Thus, during magnetically disturbed periods (magnetic storms) Kp-index reflects auroral, not the planetary, activity. Annual variation of geomagnetic activity based on Kp-index decribes annual distribution of number of magnetic storms not realistic geomagnetic activity one. Here we should have in mind that geomagnetic activity should be defined as activity integrated during the time period when there are no any storms. This situation occurs during 90% of the time of year. Besides, real dynamics of geomagnetic activity should be described by the temporal variation of the external magnetic filed in all near-Earth’s space and it could not be estimated only basing on data of Kp-stations located mostly in the Northern hemisphere. We studied seasonal variation of geomagnetic activity based on monthly distribution of index Kp (Ap). The planetary Ap-index actually is calculated as a running average of Kp-index of eight 3-hour periods. Figure 1 shows average monthly distribution of Ap-index in period 1970–2002. One can see that the peaks of monthly Kp index in March-April and October-November is caused by the most frequent occurrence of magnetic storms and extreme ones near vernal and autumnal equinoxes. Figure 1. Kp-index histogram by month based on selected of Kp-index maximum amplitude over 1970- 2002. 296 Proceedings of the 9th Intl Conf. “Problems of Geocosmos” (Oct 8-12, 2012, St. Petersburg, Russia) As it is known the planetary Kp-index is derived from the data of subauroral observatories. It is considered that each observatory is located far from any magnetospheric sources and it doesn’t responsive to geomagnetic disturbances in the auroral zone of the high latitudes. Thus, it doesn’t describe geomagnetic activity in the region where the most high-amplitude geomagnetic disturbance occur, and doesn’t estimate total geomagnetic activity over the Earth. Figure 2 demonstrates seasonal variations in monthly mean Dst, Ap, Am, AE, and PCN geomagnetic activity indices [Lyatsky, 2003]. From Figure 2 one can see that high latitude geomagnetic disturbances described by indices AE and PC are more intensive than geomagnetic activity described by index Kp(Ap on the figure). The peak area of the seasonal variations of index AE(PC) corresponds to the summer (winter) periods (maximums) because the ionospheric conductivity in the Northern Hemisphere is the largest in summer and the smallest in winter. Moreover magnetic variations of Kp- index observatories should be similar to those of auroral observatories as onecan see in Figure 3 shown variations of quantitative assessment of geomagnetic activity at some observatories during the magnetic storms of different intensity in comparison with Kp-index . Quantitative assessment of geomagnetic activity Hizm To introduce quantitative assessment of geomagnetic activity Hizm we chose H-component of the geomagnetic field recorded by observatories of the Northern hemisphere because it is more affected external sources. Our technology of the quantitative assessment of geomagnetic
Load more

Recommended publications
  • Trajectory Coordinate System Information We Have Calculated the New Horizons Trajectory and Full State Vector Information in 11 Different Coordinate Systems
    Trajectory Coordinate System Information We have calculated the New Horizons trajectory and full state vector information in 11 different coordinate systems. Below we describe the coordinate systems, and in the next section we describe the trajectory file format. Heliographic Inertial (HGI) This system is Sun centered with the X-axis along the intersection line of the ecliptic (zero longitude occurs at the +X-axis) and solar equatorial planes. The Z-axis is perpendicular to the solar equator, and the Y-axis completes the right-handed system. This coordinate system is also referred to as the Heliocentric Inertial (HCI) system. Heliocentric Aries Ecliptic Date (HAE-DATE) This coordinate system is heliocentric system with the Z-axis normal to the ecliptic plane and the X-axis pointes toward the first point of Aries on the Vernal Equinox, and the Y- axis completes the right-handed system. This coordinate system is also referred to as the Solar Ecliptic (SE) coordinate system. The word “Date” refers to the time at which one defines the Vernal Equinox. In this case the date observation is used. Heliocentric Aries Ecliptic J2000 (HAE-J2000) This coordinate system is heliocentric system with the Z-axis normal to the ecliptic plane and the X-axis pointes toward the first point of Aries on the Vernal Equinox, and the Y- axis completes the right-handed system. This coordinate system is also referred to as the Solar Ecliptic (SE) coordinate system. The label “J2000” refers to the time at which one defines the Vernal Equinox. In this case it is defined at the J2000 date, which is January 1, 2000 at noon.
    [Show full text]
  • Solar Data Handling
    United Nations Educational. Scientific The Abdus Salam International Centre for Theoretical Physics Intem3tion.1l Atomic Energy Agency 310/1749-25 ICTP-COST-USNSWP-CAWSES-INAF-INFN International Advanced School on Space Weather 2-19 May 2006 Solar Data Handling Robert BENTLEY UCL Department of Space and Climate Physics Mullard Space Science Laboratory Hombury St. Mary Dorking Surrey RH5 6NT U.K. These lecture notes are intended only for distribution to participants Strada Costiera 11, 34014 Trieste, Italy - Tel. +39 040 2240 11 I; Fax +39 040 224 163 - [email protected], www.ictp.it i f Solar data Handling 1 Rob Bentley University College London (UCL) C Mullard Space Science Laboratory Trieste, 3 May 2006 International Advanced School on Space Weather Nature of Observations Data management issues • Types of data | • Storage of data I • Access to data (current) : • Standards • Temporal and spatial coordinates • File Formats • Types of Metadata I • Data Models egso Nature of solar observations The appearance of the Sun changes dramatically with wavelength • Emissions originate from different layers in the atmosphere and different physical phenomena K • For a complete picture we need to use as 2x106K wide a range of observations as possible 1 • Mixture of types of observations • Different wavelengths and time intervals • Mixture of observations from space- and ground-based platforms 8x104K • Increasing desire to study problems that span communities • Desire relevant to Space Weather, climate I physics, planetary physics, astrophysics 3 • Identifying observations across community 6x10 K boundaries and then retrieving them are major problems r Sun at different wavelengths egso o J K I egso TVPes of Data • Types of data/observation: • single values • spectra (includes and dispersed quantity) • images | • compound - e.g.
    [Show full text]
  • Minima, When the Type B Redauroras Are Predominant. SOLAR
    VOL. 43, 1957 GEOPHYSICS: J. BARTELS 75 are being slowed down much higher in the atmosphere than occurs at sunspot minima, when the Type B red auroras are predominant. From the general physical interpretation of the observations of unusual heights of aurora, it seems probable that a consideration of the degree of ionization of the upper atmosphere may account for the wide range found in auroral heights. For this reason the degree of ionization may become one of the problems of auroral morphol- ogy. The auroral program for the International Geophysical Year, 1957-1958, was de- signed with many of the above-mentioned problems in auroral morphology in mind. Hence we may expect to have answers for some of the problems in the next two or three years. 1 J. A. Van Allen, Phys. Rev., 99, 609, 1955. 2 S. Chapman and C. G. Little, J. Atm. and Terrest. Phys. (in press). 3 J. P. Heppner, J. Geophys. Research, 59, 329, 1954. 4 C. W. Gartlein, Nat. Geographic Mag., 92, 683, 1947. 5 F. T. Davies, Transactions of the Oslo Meeting, August 19-928, 1948 (Washington: Interna- tional Union of Geodesy and Geophysics, 1950). 6 A. B. Meinel, Astrophys. J., 113, 50, 1951; 114, 431, 1951. 7 A. B. Meinel and C. Y. Fan, Astrophys. J., 115, 330, 1952. 8 H. Leinbach, Sky and Telescope, 15, 329, 1956. 9 C. T. Elvey, Seventh Alaska Science Conference, Alaska Division, AAAS, Juneau, September 26-29, 1956. 10 C. St0rmer, The Polar Aurora (Oxford: Clarendon Press, 1955). 1 M. Sugiura, Proceedings of the Third Alaska Science Conference, September 22-97, 1962, p.
    [Show full text]
  • Coordinate Systems for Solar Image Data
    A&A 449, 791–803 (2006) Astronomy DOI: 10.1051/0004-6361:20054262 & c ESO 2006 Astrophysics Coordinate systems for solar image data W. T. Thompson L-3 Communications GSI, NASA Goddard Space Flight Center, Code 612.1, Greenbelt, MD 20771, USA e-mail: [email protected] Received 27 September 2005 / Accepted 11 December 2005 ABSTRACT A set of formal systems for describing the coordinates of solar image data is proposed. These systems build on current practice in applying coordinates to solar image data. Both heliographic and heliocentric coordinates are discussed. A distinction is also drawn between heliocentric and helioprojective coordinates, where the latter takes the observer’s exact geometry into account. The extension of these coordinate systems to observations made from non-terrestial viewpoints is discussed, such as from the upcoming STEREO mission. A formal system for incorporation of these coordinates into FITS files, based on the FITS World Coordinate System, is described, together with examples. Key words. standards – Sun: general – techniques: image processing – astronomical data bases: miscellaneous – methods: data analysis 1. Introduction longitude and latitude – only need to worry about two spatial dimensions. The same can be said for normal cartography of Solar research is becoming increasingly more sophisticated. a planet such as Earth. However, to properly treat the complete Advances in solar instrumentation have led to increases in spa- range of solar phenomena, from the interior out into the corona, tial resolution, and will continue to do so. Future space mis- a complete three-dimensional coordinate system is required. sions will view the Sun from different perspectives than the Unfortunately, not all the information necessary to determine current view from ground-based observatories, or satellites in the full three-dimensional position of a solar feature is usually Earth orbit.
    [Show full text]
  • Determining the Rotation Period of the Sun
    SOLAR PHYSICS AND TERRESTRIAL EFFECTS 2+ Activity 8 4= Activity 8 Determining the Rotation Period of the Sun Relevant Reading Chapter 2, section 3 Purpose Determine the rotation period of the Sun. Although numerous methods for accurate measurement are used in solar research, the method described here, using photographs taken over several days, will allow determination to within an Earth-day. Materials Photo set that shows at least one solar feature that can be followed over a several-day period. For real challenge, take the photos yourself, or make a simple projection sketch of sunspots over several days. 1 sheet of clear plastic used for overhead transparencies or viewgraphs, or something similar such as a clear plastic report folder a mm ruler, compass and protractor a fine-tipped marking pen suitable for plastic graph paper with 1-mm squares Procedures 1. Measure, to the nearest millimeter, the diameter of the Sun on the photo taken near the middle of the data period. 2. Use a compass and draw a circle with the same diameter on the transpar- ent sheet. 3. With the circle aligned over the photo on the date used for the diameter, trace the axis orientation marks onto the transparency. 4. Pick a solar feature that traverses the solar disk for as many days as pos- sible. Align the circle on the transparency over each successive photo and carefully mark the position of the chosen solar feature along with its date. 5. Carefully draw the best fitting straight line through the marked positions and measure its length across the circle as accurately as possible.
    [Show full text]
  • On the Determination and Constancy of the Solar Oblateness
    On the determination and constancy of the solar oblateness Mustapha Meftah, Abdanour Irbah, Alain Hauchecorne, Thierry Corbard, Sylvaine Turck-Chièze, Jean-François Hochedez, Patrick Boumier, A. Chevalier, S. Dewitte, S. Mekaoui, et al. To cite this version: Mustapha Meftah, Abdanour Irbah, Alain Hauchecorne, Thierry Corbard, Sylvaine Turck-Chièze, et al.. On the determination and constancy of the solar oblateness. Solar Physics, Springer Verlag, 2015, 290 (3), pp.673-687. 10.1007/s11207-015-0655-6. hal-01110569 HAL Id: hal-01110569 https://hal.archives-ouvertes.fr/hal-01110569 Submitted on 16 Nov 2016 HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. Solar Phys (2015) 290:673–687 DOI 10.1007/s11207-015-0655-6 On the Determination and Constancy of the Solar Oblateness M. Meftah1 · A. Irbah1 · A. Hauchecorne1 · T. Corbard2 · S. Turck-Chièze3 · J.-F. Hochedez1,4 · P. Boumier 5 · A. Chevalier6 · S. Dewitte6 · S. Mekaoui6 · D. Salabert3 Received: 19 November 2013 / Accepted: 21 January 2015 / Published online: 11 February 2015 © The Author(s) 2015. This article is published with open access at Springerlink.com Abstract The equator-to-pole radius difference (r = Req −Rpol) is a fundamental property of our star, and understanding it will enrich future solar and stellar dynamical models.
    [Show full text]
  • ESA Bulletin No
    MARSDEN 6/12/03 5:08 PM Page 60 Artist’s impression of Ulysses’ exploratory mission (by D. Hardy) Science 60 esa bulletin 114 - may 2003 www.esa.int MARSDEN 6/12/03 5:08 PM Page 61 News from the Sun’s Poles News from the Sun’s Poles Courtesy of Ulysses Richard G. Marsden ESA Directorate of Scientific Programmes, ESTEC, Noordwijk, The Netherlands Edward J. Smith Jet Propulsion Laboratory, California Institute of Technology, Pasadena, USA True to its classical namesake in Dante’s Introduction Launched from Cape Canaveral more than 13 years ago, Ulysses Inferno, the ESA-NASA Ulysses mission has is well on its way to completing two full circuits of the Sun in a unique orbit that takes it over the north and south poles of our ventured into the ‘unpeopled world star. In doing so, the European-built space probe and its payload of scientific instruments have added a fundamentally new beyond the Sun’,in the pursuit of perspective to our knowledge of the bubble in space in which the Sun and the Solar System exist, called ‘the heliosphere’. ‘knowledge high’! www.esa.int esa bulletin 114 - may 2003 61 MARSDEN 6/12/03 5:09 PM Page 62 Science A small spacecraft by today’s standards, Ulysses weighed just 367 kg at launch, including its scientific payload of 55 kg. The nine scientific instruments on board measure the solar wind, the heliospheric magnetic field, natural radio emission and plasma waves, energetic particles and cosmic rays, interplanetary and interstellar dust, neutral interstellar helium atoms, and cosmic gamma-ray bursts.
    [Show full text]
  • Arxiv:1901.09083V2 [Astro-Ph.SR] 3 Jun 2019 2 University of Maryland, Department of Astronomy, College Park, MD 20742, USA
    Solar Physics DOI: 10.1007/•••••-•••-•••-••••-• What the Sudden Death of Solar Cycles Can Tell us About the Nature of the Solar Interior Scott W. McIntosh 1 · Robert J. Leamon 2,3 · Ricky Egeland 1 · Mausumi Dikpati 1 · Yuhong Fan 1 · Matthias Rempel 1 c Springer •••• Abstract We observe the abrupt end of solar activity cycles at the Sun's Equa- tor by combining almost 140 years of observations from ground and space. These \terminator" events appear to be very closely related to the onset of magnetic activity belonging to the next Solar Cycle at mid-latitudes and the polar-reversal process at high latitudes. Using multi-scale tracers of solar activity we examine the timing of these events in relation to the excitation of new activity and find that the time taken for the solar plasma to communicate this transition is of the order of one solar rotation { but could be shorter. Utilizing uniquely com- prehensive solar observations from the Solar Terrestrial Relations Observatory (STEREO) and Solar Dynamics Observatory (SDO) we see that this transitional event is strongly longitudinal in nature. Combined, these characteristics suggest that information is communicated through the solar interior rapidly. A range of possibilities exist to explain such behavior: for example gravity waves on the solar tachocline, or that the magnetic fields present in the Sun's convection zone could be very large, with a poloidal field strengths reaching 50 kG { considerably larger than conventional explorations of solar and stellar dynamos estimate. Regardless of the mechanism responsible, the rapid timescales demonstrated by the Sun's global magnetic field reconfiguration present strong constraints on first-principles numerical simulations of the solar interior and, by extension, other stars.
    [Show full text]
  • BONDE-DISSERTATION-2018.Pdf (7.905Mb)
    A STUDY OF THE GEOSPACE RESPONSE TO DYNAMIC SOLAR WIND USING THE LYON-FEDDER-MOBARRY GLOBAL MHD SIMULATION by RICHARD EDWARD FREDERICK BONDE Presented to the Faculty of the Graduate School of The University of Texas at Arlington in Partial Fulfillment of the Requirements for the Degree of DOCTOR OF PHILOSOPHY THE UNIVERSITY OF TEXAS AT ARLINGTON May 2018 Copyright © by Richard Bonde 2018 All Rights Reserved ii Acknowledgements First and foremost, I wish to thank my supervising professor, Ramon E. Lopez. It has been an honor and a privilege to work with him and be introduced to the broader space physics community. The amount of knowledge I have attained has been incredible. My only regret is that I wasn’t with the group longer. I wish to express my gratitude to my dissertation committee: Alex Weiss, Yue Deng, Zdzislaw Musielak, and Wei Chen. I appreciate the opportunity to share my research with them and the helpful discussions that followed. I would like to also thank the following people: Robert Bruntz and Mike Wiltberger for their helpful discussions; Jiangyan Wang for her help and discussions during her time at UT Arlington – it was an honor to work with you; and a special thanks goes to Kevin Pham for all of his help and support through my endless questions. I appreciate it. It has been great experience to work with undergraduates on their research during my time here. I would like to acknowledge their hard work. Our magnetopause group did well and I appreciate it. The funding for this research was supported by NASA grant NNX15AJ03G.
    [Show full text]
  • Redalyc.Climate and the Amazon
    Orinoquia ISSN: 0121-3709 [email protected] Universidad de Los Llanos Colombia Bunyard, Peter Climate and the Amazon Orinoquia, vol. 11, núm. 1, 2007, pp. 7-20 Universidad de Los Llanos Meta, Colombia Available in: http://www.redalyc.org/articulo.oa?id=89611102 How to cite Complete issue Scientific Information System More information about this article Network of Scientific Journals from Latin America, the Caribbean, Spain and Portugal Journal's homepage in redalyc.org Non-profit academic project, developed under the open access initiative Revista ORINOQUIA - Universidad de los Llanos - Villavicencio, Meta. Colombia Volumen 11 - Nº 1 - Año 2007 CONFERENCIA Climate and the Amazon Clima en el Amazonas PETER BUNYARD1 1Biólogo, PhD. Boston University, USA Recibido: 18 Mayo de 2007; Aceptado: 15 junio de 2007. When concerning ourselves with the future of the earth’s information about Brazil’s Legal Amazon. His research climate we must not make the grave mistake of counting indicates that by 1998, the area of forest cleared in only the quantities of carbon dioxide released into the the Brazilian Amazon had reached some 549,000 atmosphere from the combustion of fossil fuels, while square kilometres, about the size of France out of a neglecting those from changes in vegetation cover. But, total area as large as Western Europe. In a few decades, there is another crucial dimension too: the role of natural Brazil has managed to deforest an area far greater than ecosystems in giving us a climate we can live with. In that lost over the preceding five centuries of European this context the future of the Amazon forest is absolutely colonization.
    [Show full text]
  • The Rotation of the Sun
    THE ROTATION OF THE SUN The sun turns once every 27 days, but some parts turn faster than others. Such variations are clues to interrelated phenomena from the dense core outward to the solar wind that envelops the earth by Robert Howard hen Galileo turned his tele­ cause the gas that gives rise to them is sun's rotation. When sunspots are ob­ scope on the sun in 1610, he moving, and the amount of the shift is served with a small telescope, they ap­ Wdiscovered that there were proportional to the velOCity of the gas in pear simply as spots on the photosphere: dark spots on the solar disk. Observing the line of sight. Unfortunately for solar the bright surface of the sun that is seen the motion of the spots across the disk, observers each method has disadvan­ in ordinary white-light photographs. In he deduced that the sun rotated once in tages that limit its usefulness. larger telescopes they may appear as about 27 days. One of his contempo­ saucer-shaped depressions near the edge raries, Christoph Scheiner, undertook a iming a tracer as it crosses the disk of of the sun. Therefore it is hard to be systematic program of observing the the sun is a good technique for de­ sure that the same point in the sunspot is spots. From these observations Scheiner terminingT the solar rotation rate only if . being used for the purpose of measure­ found that the rotation period of the the tracer meets certain requirements. ment as the spot traverses the solar disk spots at higher solar latitudes was slight­ First, it must survive long enough un­ and is seen from a different angle each ly longer than that of the spots at lower changed in its appearance to be useful day.
    [Show full text]
  • Basic Astronomy Labs
    Astronomy Laboratory Exercise 22 Solar Lab The Sun (or Sol) is the nearest star to Earth. In fact, it is about 300,000 times closer to Earth than the next nearest star, Proxima Centauri. It is the only star whose surface features are clearly visible from Earth, and so it provides a glimpse into the workings of other stars. The Sun's importance can not be overstressed, for without the Sun there would be no life on Earth. This lab explores some of the features and motions of the Sun. The "surface" of the Sun can be viewed safely by projecting it onto a screen or looking through heavy filtering (such as welder's glass #14 or a special solar filter). NEVER LOOK DIRECTLY AT THE SUN, AS PERMANENT DAMAGE TO VISION MAY OCCUR! The Solar Observing Lab, Exercise 23, provides several observing exercises involving the Sun. The Sun is not a solid object, but a huge globe of glowing plasma. The "surface" that is seen through a filtered telescope or in a solar projection is the photosphere. The photosphere is that layer of the Sun from which light seems to come. But the energy of the light originates in thermonuclear fusion reactions in the core of the Sun, where hydrogen nuclei are fused into helium. The interior of the Sun can be divided into three principal parts: the core, the radiative zone, and the convective zone. In the radiative zone, light is absorbed and reemitted by the solar material. The direction in which the light is reemitted is random, so it may take millions of years for light to leave the radiative zone.
    [Show full text]