Astronomy & Astrophysics

Astronomy & Astrophysics

  • William Dean Pesnell added an answer:
    How can we analytically calculate the Hurst exponent for a periodic function?

    Let's focus on a sin(x) function. I tried using the DMA (changing sums into integrals) and the series width w(l) from Katsev & L'Hereux, Computers & Geosciences 29 (2003) 1085–1089. In the first case I got stuck with some crazy functions, and in the second (expanding logs in time series to first order as l<<T) I got... H= -1/2. I want to precisely understand why H=1 for strict periodicity.

    William Dean Pesnell

    An R/S analysis compares the properties of the time series over many different time scales. The slope of the curve then approximates the Hurst exponent. If you analyze a series with noise and a sine curve you see a discontinuity in the slope at the period of the sine curve (the Suyal et al. 2009 paper has some examples). In the absence of variations at longer timescales, such as trends, there is no information above that period to derive a slope. For the sunspot number we see a discontinuity at 11 years, just as expected, but there are longer-term signals to continue the R/S analysis at longer periods. That gives an estimate of H for the entire time series. A linear trend indeed has H=1 because the variation over a time bin is comparable to or larger than the noise within that time bin.

  • Z. Osmanov added an answer:
    Does anyone know what is the minimum level for detectability of PeV photons by modern telescopes?

    One of the important questions concerning this topic is to know sensitivity of instruments - the minimum detectable flux.

    Z. Osmanov

    Dear Dr Samvel Ter-Antonyan, thank you for the useful references


  • Gerro Prinsloo added an answer:
    How can we compute solar position at a given place on a given day and time?
    I have GPS obtained UTC time (hours, minutes, seconds), longitude(deg E), latitude (deg N) and date. I have thoroughly search on internet for step-by-step procedure to obtain solar position variables - solar zenith angle, solar azimuth angle, Sun-Earth distance. But every method is different. Some followed geometrical method while most others have some complicated formulae with varying coefficients. I never found a generalized way to obtain solar position variables. Is there any reference which provides step-by-step procedure to obtain them in the most accurate way? Can anyone provide the step-by-step procedure with equations, corresponding explanation for coefficients, accuracy of output and literature references for each equation? Please don't provide me readily available codes / functions or links on internet search.
    Gerro Prinsloo

    Dear Lakshmi

    you already have many responses, but if you require open source algorithms for sun tracking with matlab simulink or PLC or microprocessors then you can also check Chapter 3 of our free eBook for links to the code:



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      ABSTRACT: This free book details Solar-Tracking, Automatic Sun-Tracking-Systems and Solar-Trackers and Solar Energy Harvesting Mechanisms. Book and literature review is ideal for building sun tracker, sun tracker control automation, sun and moon tracking and sunshine tracking in solar applications for sun-rich countries such as the USA, Spain, Portugal, Mediterranean, Italy, Greece, Mexico, Portugal, China, India, Brazil, Chili, Argentina, South America, UAE, Saudi Arabia, Middle East, Iran, Iraq, etc. A solar harvester and tracker is a device that orients a payload toward the sun. A programmable computer based solar tracking device includes principles of solar tracking, solar tracking systems, as well as microcontroller, microprocessor and/or PC based solar tracking control to orientate solar reflectors, solar lenses, photovoltaic panels or other optical configurations towards the sun (see solar parabola calculator designer Motorized space frames and kinematic systems ensure motion dynamics and employ drive technology and gearing principles to steer optical configurations such as mangin, parabolic, conic, or cassegrain solar energy collectors to face the sun and follow the sun movement contour continuously (Download Center). The content of the book is also applicable to communication antenna satellite tracking and moon tracking algorithm source code for which links to free download links are provided, including formulas and algorithms to calculate the daily ephemeris of the sun position (and moon position ephimeris) for the years 1900 to 2035 AD and beyond. Sun tracking suitable for renewable energy systems RES concentrated solar CSP Stirling micro-CHP micro-CCHP co-generation combined cycle micro combined heat and power micro-CHCP in tri-generation, quad-generation and poly-generation with smart-microgrid and smartgrid applications in remote power systems and isolated microgrid for decentralized energy power systems.. In harnessing power from the sun through a solar tracker or practical solar tracking system, renewable energy control automation systems require automatic solar tracking software and solar position algorithms to accomplish dynamic motion control with control automation architecture, circuit boards and hardware. On-axis sun tracking system such as the altitude-azimuth dual axis or multi-axis solar tracker systems use a sun tracking algorithm or ray tracing sensors or software to ensure the sun's passage through the sky is traced with high precision in automated solar tracker applications, right through summer solstice, solar equinox and winter solstice (seguimiento solar y automatización, automatización seguidor solar, tracking solar e automação, automação seguidor solar, inseguimento solare, inseguitore solare, energia termica, sole seguito, posizionatore motorizzato) . From sun tracing software perspective, the sonnet Tracing The Sun has a literal meaning. Within the context of sun track and trace, this book explains that the sun's daily path across the sky is directed by relatively simple principles, and if grasped/understood, then it is relatively easy to trace the sun with sun following software. Sun position computer software and the physics behind tracing the sun are available as open source code, sources that is listed in this book. Ironically there was even a system called sun chaser, said to have been a solar positioner system known for chasing the sun throughout the day. Using solar equations in an electronic circuit for solar tracking is quite simple, even if you are a novice, but mathematical solar equations are over complicated by academic experts and professors in text-books, journal articles and internet websites. In terms of solar hobbies, scholars, students and Hobbyist's looking at solar tracking electronics or PC programs for solar tracking are usually overcome by the sheer volume of scientific material and internet resources, which leaves many developers in frustration when search for simple experimental solar tracking source-code for their on-axis sun-tracking systems. This booklet will simplify the search for the mystical sun tracking formulas for your sun tracker innovation and help you develop your own autonomous solar tracking controller. By directing the solar collector directly into the sun, a solar harvesting means or device can harness sunlight or thermal heat. This is achieved with the help of sun angle formulas, solar angle formulas or solar tracking procedures for the calculation of sun's position in the sky. Automatic sun tracking system software includes algorithms for solar altitude azimuth angle calculations required in following the sun across the sky. In using the longitude, latitude GPS coordinates of the solar tracker location, these sun tracking software tools supports precision solar tracking by determining the solar altitude-azimuth coordinates for the sun trajectory in altitude-azimuth tracking at the tracker location, using certain sun angle formulas in sun vector calculations. Instead of follow the sun software, a sun tracking sensor such as a sun sensor or webcam or video camera with vision based sun following image processing software can also be used to determine the position of the sun optically. Such optical feedback devices are often used in solar panel tracking systems and dish tracking systems. Dynamic sun tracing is also used in solar surveying, DNI analyser and sun surveying systems that build solar infographics maps with solar radiance, irradiance and DNI models for GIS (geographical information system). In this way geospatial methods on solar/environment interaction makes use use of geospatial technologies (GIS, Remote Sensing, and Cartography). Climatic data and weather station or weather center data, as well as queries from sky servers and solar resource database systems (i.e. on DB2, Sybase, Oracle, SQL, MySQL) may also be associated with solar GIS maps. In such solar resource modelling systems, a pyranometer or solarimeter is normally used in addition to measure direct and indirect, scattered, dispersed, reflective radiation for a particular geographical location. Sunlight analysis is important in flash photography where photographic lighting are important for photographers. GIS systems are used by architects who add sun shadow applets to study architectural shading or sun shadow analysis, solar flux calculations, optical modelling or to perform weather modelling. Such systems often employ a computer operated telescope type mechanism with ray tracing program software as a solar navigator or sun tracer that determines the solar position and intensity. The purpose of this booklet is to assist developers to track and trace suitable source-code and solar tracking algorithms for their application, whether a hobbyist, scientist, technician or engineer. Many open-source sun following and tracking algorithms and source-code for solar tracking programs and modules are freely available to download on the internet today. Certain proprietary solar tracker kits and solar tracking controllers include a software development kit SDK for its application programming interface API attributes (Pebble). Widget libraries, widget toolkits, GUI toolkit and UX libraries with graphical control elements are also available to construct the graphical user interface (GUI) for your solar tracking or solar power monitoring program. The solar library used by solar position calculators, solar simulation software and solar contour calculators include machine program code for the solar hardware controller which are software programmed into Micro-controllers, Programmable Logic Controllers PLC, programmable gate arrays, Arduino processor or PIC processor. PC based solar tracking is also high in demand using C++, Visual Basic VB, as well as MS Windows, Linux and Apple Mac based operating systems for sun path tables on Matlab, Excel. Some books and internet webpages use other terms, such as: sun angle calculator, sun position calculator or solar angle calculator. As said, such software code calculate the solar azimuth angle, solar altitude angle, solar elevation angle or the solar Zenith angle (Zenith solar angle is simply referenced from vertical plane, the mirror of the elevation angle measured from the horizontal or ground plane level). Similar software code is also used in solar calculator apps or the solar power calculator apps for IOS and Android smartphone devices. Most of these smartphone solar mobile apps show the sun path and sun-angles for any location and date over a 24 hour period. Some smartphones include augmented reality features in which you can physically see and look at the solar path through your cell phone camera or mobile phone camera at your phone's specific GPS location. In the computer programming and digital signal processing (DSP) environment, (free/open source) program code are available for VB, .Net, Delphi, Python, C#, C+, C++, Swift, ADM, F#, Flash, Basic, QBasic, GBasic, KBasic, SIMPL language, Squirrel, Solaris, Assembly language on operating systems such as MS Windows, Apple Mac, DOS or Linux OS. Software algorithms predicting position of the sun in the sky are commonly available as graphical programming platforms such as Matlab (Mathworks), Simulink models, Java applets, TRNSYS simulations, Scada system apps, Labview module, Beckhoff TwinCAT (Visual Studio), Siemens SPA, mobile and iphone apps, Android or iOS tablet apps, and so forth. At the same time, PLC software code for a range of sun tracking automation technology can follow the profile of sun in sky for Siemens, HP, Panasonic, ABB, Allan Bradley, OMRON, SEW, Festo, Beckhoff, Rockwell, Schneider, Endress Hauser, Fudji electric. Honeywell, Fuchs, Yokonawa, or Muthibishi platforms. Sun path projection software are also available for a range of modular IPC embedded PC motherboards, Industrial PC, PLC (Programmable Logic Controller) and PAC (Programmable Automation Controller) such as the Siemens S7-1200 or Siemens Logo, Beckhoff IPC or CX series, OMRON PLC, Ercam PLC, AC500plc ABB, National Instruments NI PXI or NI cRIO, PIC processor, Intel 8051/8085, IBM (Cell, Power, Brain or Truenorth series), FPGA (Xilinx Altera Nios), Xeon, Atmel megaAVR, or Arduino AtMega microcontroller, with servo motor, stepper motor, direct current DC pulse width modulation PWM (current driver) or alternating current AC SPS or IPC variable frequency drives VFD motor drives (also termed adjustable-frequency drive, variable-speed drive, AC drive, micro drive or inverter drive) for electrical, mechatronic, pneumatic, or hydraulic solar tracking actuators. The above motion control and robot control systems include analogue or digital interfacing ports on the processors to allow for tracker angle orientation feedback control through one or a combination of angle sensor or angle encoder, shaft encoder, precision encoder, optical encoder, magnetic encoder, direction encoder, rotational encoder, chip encoder, tilt sensor, inclination sensor, or pitch sensor. Note that the tracker's elevation or zenith axis angle may measured using an altitude angle-, declination angle-, inclination angle-, pitch angle-, or vertical angle-, zenith angle- sensor or inclinometer. Similarly the tracker's azimuth axis angle be measured with a azimuth angle-, horizontal angle-, or roll angle- sensor. Chip integrated accelerometer magnetometer gyroscope type angle sensors can also be used to calculate displacement. Other options include the use of thermal imaging systems such as a Fluke thermal imager, or robotic or vision based solar tracker systems that employ face tracking, head tracking, hand tracking, eye tracking and car tracking principles in solar tracking. With unattended decentralised rural, island, isolated, or autonomous off-grid power installations, remote control, monitoring, data acquisition, digital datalogging and online measurement and verification equipment becomes crucial. It assists the operator with supervisory control to monitor the efficiency of remote renewable energy resources and systems and provide valuable web-based feedback in terms of CO2 and clean development mechanism (CDM) reporting. A power quality analyser for diagnostics through internet, WiFi and cellular mobile links is most valuable in frontline troubleshooting and predictive maintenance, where quick diagnostic analysis is required to detect and prevent power quality issues. Solar tracker applications cover a wide spectrum of solar energy and concentrated solar devices, including solar power generation, solar desalination, solar water purification, solar steam generation, solar electricity generation, solar industrial process heat, solar thermal heat storage, solar food dryers, solar water pumping, hydrogen production from methane or producing hydrogen and oxygen from water (HHO) through electrolysis. Many patented or non-patented solar apparatus include tracking in solar apparatus for solar electric generator, solar desalinator, solar steam engine, solar ice maker, solar water purifier, solar cooling, solar refrigeration, USB solar charger, solar phone charging, portable solar charging tracker, solar coffee brewing, solar cooking or solar dying means. Your project may be the next breakthrough or patent, but your invention is held back by frustration in search for the sun tracker you require for your solar powered appliance, solar generator, solar tracker robot, solar freezer, solar cooker, solar drier, solar pump, solar freezer, or solar dryer project. Whether your solar electronic circuit diagram include a simplified solar controller design in a solar electricity project, solar power kit, solar hobby kit, solar steam generator, solar hot water system, solar ice maker, solar desalinator, hobbyist solar panels, hobby robot, or if you are developing professional or hobby electronics for a solar utility or micro scale solar powerplant for your own solar farm or solar farming, this publication may help accelerate the development of your solar tracking innovation. Lately, solar polygeneration, solar trigeneration (solar triple generation), and solar quad generation (adding delivery of steam, liquid/gaseous fuel, or capture food-grade CO2) systems have need for automatic solar tracking. These systems are known for significant efficiency increases in energy yield as a result of the integration and re-use of waste or residual heat and are suitable for compact packaged micro solar powerplants that could be manufactured and transported in kit-form and operate on a plug-and play basis. Typical hybrid solar power systems include compact or packaged solar micro combined heat and power (CHP or mCHP) or solar micro combined, cooling, heating and power (CCHP, CHPC, mCCHP, or mCHPC) systems used in distributed power generation. These systems are often combined in concentrated solar CSP and CPV smart microgrid configurations for off-grid rural, island or isolated microgrid, minigrid and distributed power renewable energy systems. Solar tracking algorithms are also used in modelling of trigeneration systems using TrnSys, Matlab and Simulink platforms as well as in automation and control of renewable energy systems through intelligent parsing, multi-objective, adaptive learning control and control optimization strategies. Solar tracking algorithms also find application in developing solar models for country or location specific solar studies, for example in terms of measuring or analysis of the fluctuations of the solar radiation (i.e. direct and diffuse radiation) in a particular area. Solar DNI, solar irradiance and atmospheric information and models can thus be integrated into a solar map, solar atlas or geographical information systems (GIS). Such models allows for defining local parameters for specific regions that may be valuable in terms of the evaluation of different solar in photovoltaic of CSP systems on simulation and synthesis platforms such as Matlab and Simulink or in linear or multi-objective optimization algorithm platforms such as COMPOSE, EnergyPLAN or DER-CAM. A dual-axis solar tracker and single-axis solar tracker may use a sun tracker program or sun tracker algorithm to position a solar dish, solar panel array, heliostat array, PV panel, solar antenna or infrared solar nantenna. A self-tracking solar concentrator performs automatic solar tracking by computing the solar vector. Solar position algorithms (TwinCAT, SPA, or PSA Algorithms) use an astronomical algorithm to calculate the position of the sun. It uses astronomical software algorithms and equations for solar tracking in the calculation of sun's position in the sky for each location on the earth at any time of day. Like an optical solar telescope, the solar position algorithm pin-points the solar reflector at the sun and locks onto the sun's position to track the sun across the sky as the sun progresses throughout the day. Optical sensors such as photodiodes, light-dependant-resistors (LDR) or photoresistors are used as optical accuracy feedback devices. Lately we also included a section in the book (with links to microprocessor code) on how the PixArt Wii infrared camera in the Wii remote or Wiimote may be used in infrared solar tracking applications. In order to harvest free energy from the sun, some automatic solar positioning systems use an optical means to direct the solar tracking device. These solar tracking strategies use optical tracking techniques, such as a sun sensor means, to direct sun rays onto a silicon or CMOS substrate to determine the X and Y coordinates of the sun's position. In a solar mems sun-sensor device, incident sunlight enters the sun sensor through a small pin-hole in a mask plate where light is exposed to a silicon substrate. In a web-camera or camera image processing sun tracking and sun following means, object tracking software performs multi object tracking or moving object tracking methods. In an solar object tracking technique, image processing software performs mathematical processing to box the outline of the apparent solar disc or sun blob within the captured image frame, while sun-localization is performed with an edge detection algorithm to determine the solar vector coordinates. An automated positioning system help maximize the yields of solar power plants through solar tracking control to harness sun's energy. In such renewable energy systems, the solar panel positioning system uses a sun tracking techniques and a solar angle calculator in positioning PV panels in photovoltaic systems and concentrated photovoltaic CPV systems. Automatic on-axis solar tracking in a PV solar tracking system can be dual-axis sun tracking or single-axis sun solar tracking. It is known that a motorized positioning system in a photovoltaic panel tracker increase energy yield and ensures increased power output, even in a single axis solar tracking configuration. Other applications such as robotic solar tracker or robotic solar tracking system uses robotica with artificial intelligence in the control optimization of energy yield in solar harvesting through a robotic tracking system. Automatic positioning systems in solar tracking designs are also used in other free energy generators, such as concentrated solar thermal power CSP, dish Stirling systems and concentrated solar power systems for absorption chillers. The sun tracking device in a solar collector in a solar concentrator or solar collector Such a performs on-axis solar tracking, a dual axis solar tracker assists to harness energy from the sun through an optical solar collector, which can be a parabolic mirror, parabolic reflector, Fresnel lens or mirror array/matrix. A parabolic dish or reflector is dynamically steered using a transmission system or solar tracking slew drive mean. In steering the dish to face the sun, the power dish actuator and actuation means in a parabolic dish system optically focusses the sun's energy on the focal point of a parabolic dish or solar concentrating means. A Stirling engine, solar heat pipe, thermosyphin, solar phase change material PCM receiver, or a fibre optic sunlight receiver means is located at the focal point of the solar concentrator. The dish Stirling engine configuration is referred to as a dish Stirling system or Stirling power generation system. Hybrid solar power systems (used in combination with biogas, biofuel, petrol, ethanol, diesel, natural gas or PNG) use a combination of power sources to harness and store solar energy in a storage medium. Any multitude of energy sources can be combined through the use of controllers and the energy stored in batteries, phase change material, thermal heat storage, and in cogeneration form converted to the required power using thermodynamic cycles (organic Rankin, Brayton cycle, micro turbine, Stiling) with an inverter and charge controller. Using exergy analysis principles, several exergetic variables are used to identify the strength and limitations of a system. Book is ideal for solar applications in sun rich countries such as Spain, Mediterranean, Italy, Greece, Mexico, Portugal, China, India, Brazil, Chili, Argentina, etc. В этой книге подробно Автоматическая Solar-Tracking, ВС-Tracking-Systems, Solar-трекеры и ВС Tracker Systems. Интеллектуальный автоматический солнечной слежения является устройством, которое ориентирует полезную нагрузку к солнцу. Такое программируемый компьютер на основе солнечной устройство слежения включает принципы солнечной слежения, солнечных систем слежения, а также микроконтроллер, микропроцессор и / или ПК на базе управления солнечной отслеживания ориентироваться солнечных отражателей, солнечные линзы, фотоэлектрические панели или другие оптические конфигурации к ВС Моторизованные космические кадры и кинематические системы обеспечения динамики движения и использовать приводной техники и готовится принципы, чтобы направить оптические конфигурации, такие как Манжен, параболических, конических или Кассегрена солнечных коллекторов энергии, чтобы лицом к солнцу и следовать за солнцем контур движения непрерывно. В обуздывать силу от солнца через солнечный трекер или практической солнечной системы слежения, системы возобновляемых контроля энергии автоматизации требуют автоматического солнечной отслеживания программного обеспечения и алгоритмов солнечные позиции для достижения динамического контроля движения с архитектуры автоматизации управления, печатных плат и аппаратных средств. На оси системы слежения ВС, таких как высота-азимут двойной оси или многоосевые солнечные системы трекер использовать алгоритм отслеживания солнце или трассировки лучей датчиков или программное обеспечение, чтобы обеспечить прохождение солнца по небу прослеживается с высокой точностью в автоматизированных приложений Солнечная Tracker , прямо через летнего солнцестояния, солнечного равноденствия и зимнего солнцестояния.Высокая точность позиции ВС калькулятор или положение солнца алгоритм это важный шаг в проектировании и строительстве автоматической системой солнечной слежения. 这本书详细介绍了全自动太阳能跟踪,太阳跟踪系统的出现,太阳能跟踪器和太阳跟踪系统。智能全自动太阳能跟踪器是定向向着太阳的有效载荷设备。这种可编程计算机的太阳能跟踪装置,包括太阳跟踪,太阳能跟踪系统,以及微控制器,微处理器和/或基于PC机的太阳跟踪控制,以定向太阳能反射器,太阳透镜,光电板或其他光学配置朝向太阳的原理。机动空间框架和运动系统,确保运动动力学和采用的驱动技术和传动原理引导光学配置,如曼金,抛物线,圆锥曲线,或卡塞格林式太阳能集热器面向太阳,不断跟随太阳运动的轮廓。 从阳光透过太阳能跟踪器或实用的太阳能跟踪系统利用电力,可再生能源控制的自动化系统需要自动太阳跟踪软件和太阳位置算法来实现控制与自动化架构,电路板和硬件的动态运动控制。上轴太阳跟踪系统,如高度,方位角双轴或多轴太阳跟踪系统使用太阳跟踪算法或光线追踪传感器或软件,以确保通过天空中太阳的通道被跟踪的高精度的自动太阳跟踪器的应用,通过正确的夏至,春分太阳和冬至。一种高精度太阳位置计算器或太阳位置算法是这样的自动太阳能跟踪系统的设计和施工中的重要一步。 This Solar Tracking Practical Research eBook for Apple iPad, Barnes and Noble Nook, Sony Reader, BeBook, Adobe Digital Editions, Lexcycle Stanza, BookGlutton, AZARDI, Aldiko, WordPlayer on Android Mozilla Firefox add-on OpenBerg Lector can be down be downloaded on the link:
      eBook 08/2014; eBook., ISBN: ISBN: 978-0-620-61576-1
  • D D Pawar added an answer:
    What is the use of dark energy in f(r,t) theory?

    Can we get any help of dark energy momentum tensor in f(r,t) theory?

    D D Pawar

    Thank  You So much...for the valuable answers!!

  • Oliver Manuel added an answer:
    Is the Sun a pulsar?
    Overwhelming experimental evidence from precise measurements shown in three figures indicate:

    _ 1. Neutron repulsion is the source of energy in cores of heavy atoms and stars
    _ 2. The Sun made our elements, birthed the solar system and sustains our lives
    _ 3. Iron-56 is the most abundant and most stable atom in the Earth and the Sun
    Oliver Manuel

    The Sun's pulsar core was probably first recognized by PAUL KAZUO KURODA while standing in the ruins of Hiroshima in August 1945:

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      ABSTRACT: Thirty-five years ago, Peter Toth asked here, "Is the Sun a pulsar?" [1]. The unequivocal answer from scientific measurements and observations since the time Hiroshima was destroyed on 6 August 1945: "Yes, the Sun is a pulsar." As Kuroda [2] suspected, standing in the ashes of Hiroshima in August 1945, "The sight before my eyes was just like the end of the world, but I also felt that the beginning of the world may have been just like this." – p. 2 The same nuclear force in cores of U atoms that destroyed Hiroshima, is the force in the core of the Sun that made our elements, birthed the Solar System [3], sustained the origin and evolution of life [4], and endowed mankind with intangible qualities -like creativity, faith, hope and love – and the unalienable right [5] to self-governance to live happy, joyous and free. That nuclear force is the fountain of energy from which chains of cause and effect flow out of cores of galaxies and stars, causing the whole universe to expand as compressed neutrons become interstellar hydrogen atoms [6]. Since ejection [3], the edge of the solar system has moved about 18 billion km (18 Gkm) from the Sun [7]. About ten billion, billion (10 19) Earths could now fit inside the gigantic "sphere of influence" of the Sun's pulsar core. The Sun induces abrupt changes in Earth's radiation belt [8] and "has been a driver of these systems more than we had any right to expect," Dr. Daniel Baker just reported at the AGU meeting on 4 December 2012 [8]. Past policies and technologies that ignored the dominant influence of the nearby pulsar face increasing opposition and fear from the public [9,10].
  • Vikram Zaveri added an answer:
    Can we use Kepler's third law to calculate orbital period of a star in a galaxy?

    Kepler's third law yields correct orbital periods for the planets of the solar system
    however, orbital period of the Sun in the Milky Way is computed with the relation    P = 2*pi*r/v.  Analysis given in the article "Supplement to periodic relativity" shows that we can obtain same result by introducing proper time in the form of deviation factor into Kepler's third law. This deviation to flat Minkowski metric satisfies Einstein's field equations and also provides solution to rotation curves of galaxies.

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      ABSTRACT: Additional explanation relating to derivation of deflection of light is presented. Curvilinear acceleration is distinguished from the Newtonian polar conic acceleration. The diference between the two is due to the curvature term. Lorentz invariant expression for acceleration is derived. Theory of rotation curves of galaxies based on second solution to Einstein's field equation is presented. Unification of periodic relativity and quantum mechanics results in periodic quantum gravity and cosmology theory.
    Vikram Zaveri

    Following article is now published in "Progress in Physics"
    Zaveri V.H., Periodic relativity: deflection of light, acceleration, rotation curves. Progress in Physics, 2015, v.11(1), 43-49.

  • Hassan Sedaghat added an answer:
    Do dark matter and dark energy constitute valid evidence of large spatial dimensions higher than 3?
    There are speculations that the gravitational effects of matter in 4 or greater LARGE spatial dimensions might account for the substantial discrepancy that exists between measured gravitational effects on normal baryonic matter and the amount of that matter that exists according to measurements. Could we be measuring the gravitational effects of "normal" matter in higher dimensions? And can large higher dimensions also explain the huge amount of dark energy that seems to be around?
    Hassan Sedaghat

    Thomas, thank you for sending the second chapter of your book. The correlations idea adds another angle from which to look at this issue. 

  • Richard Gauthier added an answer:
    Why are mainstream physicists against the super luminal physics?

    Why are mainstream physicist generally against theories, which describe faster than speed motion or communication? Is it proven in experimentally that it cannot happen or is it just a bias based on reputation of the existing theories? There are 2 very good papers about faster than light relativity listed at the bottom. Has someone refuted them on specifics?

    The papers are: .

    + 1 more attachment

    Richard Gauthier

    Hello Nainan,

    It is clear that you are a materialist and that you think that you know what matter is--the fundamental substance of the material world, and the material world is the only real world for you. You are welcome to your circular opinion, but please do not think that it is logical, or scientific. There is no scientific reason to think that the substance of matter is matter. Substance is that on which matter stands, and that substance does not have to be material-- it may be energy, it may be consciousness, it may be something non-material. Matter is a concept used to help unify our sense impressions, which are surely mental and not material. And concepts are mental also.

    with best wishes,


  • Fabio Salvaggio added an answer:
    What kind of camera do I need to do transit photometry?

    I am working with a small group of students at Hamline University on observing an exoplanet using transit photometry.

    Right now, our group is working on buying equipment. The school already has Celestron C-8 telescopes with motorized mounts available for us to use, but we don't have a camera. We need a camera that we can use to take a long-exposure photograph of a single star, and it needs to be able to measure the brightness of the star very accurately.

    Our budget is about $1,000, but the cheaper the better. So far, the only camera under $1,000 I have found that might work is the Atik Titan.  One person I asked about this camera said that the anti-blooming technology might cause problems, and that the chip in the Atik Titan is too small.  This person proposed the ST-402ME as a better model, but it costs $1,500.

    Does anyone know either of these cameras would be sufficient for our project?  Is it worth the extra money to buy the ST-402? Or do you have any other recommendations?

    Many thanks in advance for any help!

    + 2 more attachments

    Fabio Salvaggio

    I always used SBIG ST cameras. ST7 and ST8. I'm pretty sure you can find them as used with a good price (ST7 for sure). With these cameras I achieved great precision (better than 0.002) with a C9.25 at f/10. You can see in my blog ( translate it and go in exoplanet category) and in some paper I published.

  • Patrice Poyet added an answer:
    Telescope for amateur astronomy.
    I am a researcher at a science education project in Palestine and I coordinate for an informal science program. Many of the students I work with are interested in astronomy and space. I would like to purchase a telescope for amateur astronomy so as to maintain their interest and have astronomy-related activities at our center. I have been researching for the best amateur astronomy telescope and I have asked for advice, but I would like to hear your thoughts as experts in astronomy. One of the telescopes I am currently looking at is Celestron's CGEM - 1100 Computerized Telescope, what are your thoughts on this one? I truly appreciate any feedback / advice you may provide.
    Patrice Poyet

    I would strongly recommend to make it as it will teach your young students a lot of things and make them share a great adventure. The book from Texereau is perfect for that

    Would you like to have a look at the telescopes I built myself got to:



  • Dmitri Martila added an answer:
    Which experiment can determine if our universe is hologram or not?

    Which experiment can determine if our universe is hologram or not?

    Is it confirmed yet or still is it an open question?


    Bhushan Poojary.

    Dmitri Martila

    @Indranil Banik

    Perhaps you find it amusing: "Entropy of Real Pendulum"

  • David Iain Pontin added an answer:
    What are the fan and spine reconnections in the 3D magnetic reconnection of the solar corona?

    How do the fan and spine reconnections take place?

    David Iain Pontin

    This terminology refers to magnetic reconnection in the vicinity of a three-dimensional magnetic null point (a point in space at which the magnetic field strength is zero). Electric current sheets can form in various configurations around these points in response to different external forces, leading to different types of reconnection. A summary of the properties of these types of reconnection, as well as references to various articles with further details, can be found in the attached review.

    • Source
      [Show abstract] [Hide abstract]
      ABSTRACT: The magnetic field in many astrophysical plasmas -- such as the Solar corona and Earth's magnetosphere -- has been shown to have a highly complex, three-dimensional structure. Recent advances in theory and computational simulations have shown that reconnection in these fields also has a three-dimensional nature, in contrast to the widely used two-dimensional (or 2.5-dimensional) models. Here we discuss the underlying theory of three-dimensional magnetic reconnection. We also review a selection of new models that illustrate the current state of the art, as well as highlighting the complexity of energy release processes mediated by reconnection in complicated three-dimensional magnetic fields.
      Advances in Space Research 01/2011; 47(9-47):1508-1522. DOI:10.1016/j.asr.2010.12.022
  • Nainan Varghese added an answer:
    What is the charge of a black hole?
    What the charge of a black hole?
    Neutral? I hope not.
    Anyone know of any articles in this area?
    Nainan Varghese

    You may know certain properties of Electric charge. But, what is electric charge? See:

    Except for its excessive matter-content, a black hole is like any other macro body. It has no mysterious properties. See:

    Electric charges are related to electric fields rather than to macro bodies, which produce electric fields.


  • Nainan Varghese added an answer:
    How can I calculate the Earth's orbit, or what is the equation that enable us know its velocity vs. position at given time?


    Nainan Varghese

    Current planetary laws were derived from relative positions of sun and few planets. Hence, they can be used to predict their relative positions only. True orbital paths of planets are different from elliptical/circular paths described in text books. Please see:


  • Daniel Pfenniger added an answer:
    Can anyone help me with a question about neutrinos?

    I recently read a paper saying that, apart from those coming from stars, supenovae, cosmic rays and nuclear power plants, the majority of all the neutrinos in our universe were created at the big bang. But, considering that neutrinos are very elusive particles, that they travel almost at the speed of light and in straight lines, I think they all should be now near the boundary of the universe.

    How come that we can observe them? Is my reasoning above not right?

    Daniel Pfenniger

    Cosmologists keep saying the neutrino background has temperature T=1.9K while actually they want to say that their energy corresponds to kT, with k Boltzmann's constant.  This habit comes from the time neutrinos were commonly assumed to be massless.  In that case, like for photons, energy can be assimilated to a temperature because if they would thermalize with a thermometer a temperature T would be measured.

    But since neutrinos are massive, nowadays a substantial part of their energy is in their rest mass c^2.  A thermometer only measures the random kinetic energy part.  The  temperature that would be measured  if a huge thermometer would be brought to thermal equilibrium with the the neutrino background would be rather in the 0.001K range (depending on their still uncertain actual mass).

  • Dmitri Martila added an answer:
    Could some of the fundamental constants be functions of the gravitational potential?

    Based on several assumptions to deduce a cosmological model with three fundamental constants including the speed of light in vacuum, the Planck constant, and the gravitational constant, along with the dimensionless electroweak coupling constant turned into functions of the gravitational potential. Initial research of this model has indicated solutions to avoid the singularity in both special relativity and general relativity.

    • Source
      [Show abstract] [Hide abstract]
      ABSTRACT: Based on several assumptions to deduce a cosmological model with three fundamental constants along with the dimensionless electroweak coupling constant turned into functions of the gravitational potential. Initial research of this model has indicated solutions to avoid the singularity in both special relativity and general relativity.
    Dmitri Martila

    The varying Gravitational Constant needs the Dark Matter to satisfy the General Relativity, in the manner described in my book:

  • Dmitri Martila added an answer:
    Does inflating a Planck-scale wormhole to macroscopic size add internal space and "transit capacity", or do its internal measurements remain tiny?

    What does it actually mean when we talk about “inflating” a wormhole? If we find a Planck-scale natural wormhole, and we cram exotic matter into its two mouths to stretch it up to, say, one metre wide, then the wormhole may nominally now be a metre across … but have we actually added any additional useful space to the throat interior, or have we taken a throat that only has a fixed amount of internal space and "stretched" that fixed space, so that although it's now nominally one metre across, the internal measurement (and the wormhole's “capacity” as measured with internal rulers) might still be Planck-scale?

    Would inflation be adding more space and more useful “transit capacity” to the wormhole throat, or would we still have the original Planck-scale throat, inhabiting a distorted and stretched region of space in which everything is rescaled and magnified?

    Dmitri Martila

    Dear Baird, let solve your question  mathematically. The Ellis Wormhole is

    ds^2 = -dt^2 + dr^2/(1-m^2/r^2) + r^2 (d\theta^2+sin^2\theta d\phi^2). (1) The rescaled one (factor is n=const) has interval dS = ds/n, thus the metric

    dS^2 = (-dt^2 + dr^2/(1-m^2/r^2) + r^2 (d\theta^2+sin^2\theta d\phi^2))/n^2. (2)

    Hereby to preserve the shape of the motion of test particles, one has to write m = M n, because coordinate transformation  R= r/n, T=t/n then produces the original form of the metric dS^2 = -dT^2 + dR^2/(1-M^2/R^2) + R^2 (d\theta^2+sin^2\theta d\phi^2). (3) It is the metric in rescaled coordinates. Has it more matter than the original metric? Not, because the radius of the rescaled "throat" is R = M = m/n. Which is less, then original throat. So the making wormhole smaller means the removing of "exotic matter" (that shows the integral of T^t_t).

    Therefore, to inflate the Planck wormhole one requires the "exotic matter". Therefore the inflated and not inflated wormholes are not equivalent.

    However, the Schwarzschild Wormhole ds^2 = -dt^2 + dr^2/(1-2m/r) + r^2 (d\theta^2+sin^2\theta d\phi^2) has T^t_t = 0. So indeed, the size of the throat is not directly linked to the amount of exotic matter for such wormhole (4) and your theory may hold. However, I have the book (look my profile), which tells, that hypothetical "exotic matter" is not matter.

  • Biplob Sarkar added an answer:
    Are jets in AGNs or X-ray binaries leptonic e- - e+, or they can they be also baryonic?

    In the literature we find that relativistic e- - e+ jets are not possible. For truly relativistic jests, we need to have e- - p pairs.

    Biplob Sarkar

    Thanks Bothun and Rajiv for your answers.

  • John Wyndham added an answer:
    Has the important astronomical event, supernova 1054 in constellation Taurus, played any role in the discovery of pulsars?
    I know that the development of radio astronomy was the most crucial step in the discovery, but still I am convinced that the supernova 1054 may have had some inspiring role in the discovery of pulsars.
    John Wyndham

    About myself:

    I have not worked in the field of Radio Astronomy since leaving Caltech in 1967.

    My purpose in joining ResearchGate was to feature my recent researches into the Science of 9/11.  A paper presented at the 2014 IEEE International Conference on Ethics in Science, Engineering etc (May 23-26, 2014, Chicago) is awaiting publication in the IEEE proceedings for this conference. The title of the paper is "Ethics and the Official Reports about the Destruction of the World Trade Center Twin Towers (WTC1 and WTC2) on 9/11: A Case Study" by John D. Wyndham, Wayne H. Coste, and Michael R. Smith.

  • Navtej Singh added an answer:
    Which of the following is better at plotting 3D graphs, Vectors and Contours, for astrophysical systems, Matlab, Surfer, SuperMongo or Gnuplot?

    It would be helpful if the explanations are given for 3 categories:

    1. Beginners using GUI

    2. Wannabes using both GUI and TUI

    3. Experts using TUI

    Navtej Singh

    If you go the python way then another excellent library for scientific 3D plotting and visualization is Mayavi from Enthought.

    It can be installed as part of Enthought's Canopy IDE, which is free for academic use.

  • Ken Schatten added an answer:
    How can you get the temperature of a sunspot?

    Hello, im working on a research regarding the correlation of the magnetic flux and different sunspot properties. And so far, there is no archive that has the data I need, is there an archive you could recommend that has the temperature for all sunspots which appeared from 2000-2005? or any equation that can give an approximation of a sunspot's temperature? 

    Ken Schatten

    To me , the interesting thing is the Energy flux in sunspots, and how it radiates, and

    the various energy transport mechanisms into and out of, the Sunspot..

    I think the sigma T^4 formula is not bad for just trying to get some idea of a rough

    temperature.. As Roger says, of course, there are complexitites involving the complex matter of light flowing into the sunspot, and all the "lines" in the atmosphere inside the spot, so , it is a very complex problem... To me, one can get totally overwhelmed by the complexity of nature, so perhaps some simple flat bottom to the sunspot, and a kind of chromospheric atmosphere above it, in a plane parallel approximation would do

    well, to make some kind of associattion of temperature and radiated flux, etc...

    There are many interesting variations, i think, in sunspots, as to whether they are growing, or shrinking too. as well as the various complexities as to whether one can view them as a bunch of field lines that inhibit the radiation into the spot, and that is why they are cold (Biermann), or that the convective energy transport and the downflows below the spot cool it, by taking neutral hydrogen from the photosphere to cool the energy transport into the spot... The dynamical approach is one that Gene Parker developed, and the equivalent "ion hurricane" approach one that i and my colleague Hans Mayr used in a simple analogy with our terrestrial atmospheric  situation... 

    Anyway, they give us various questions to ponder that allow distractions from Earth.

  • Igor Piskarev added an answer:
    Is there a reasonable alternative to the theory of the expanding universe?
    We know that our star, the Sun loses about 10^-14 of its mass per year as a result of electromagnetic radiation and particle emission. That reduction in mass should show up as a decreasing gravitational red shift. Same thing should happen to entire galaxies. But isn't it true that the galaxies we observe that are farther from Earth are also the younger we see (because light has taken millions of years more to come to us) and, as a consequence the more massive when we consider entire galaxies? (Because we cannot possibly see them as they are, but as they were millions of years ago.) Shouldn't we expect, correspondingly that the gravitational red shift of an observed galaxy will increase with its distance to Earth?
    Igor Piskarev

    Red shift may be not Doppler's red shift at all, but absorbtion im matter, as vacuum is relict radiation (some kind of matter)

  • R. Teixeira added an answer:
    What is currently the most accurate star catalogue to use for astrometric purposes?
    There are many star catalogues available, which star catalogue is currently the most accurate (maybe the USNO CCD Astrograph Catalog, UCAC4)?
    R. Teixeira

    In Ducourant et al. 2014 we have looked for the consensual proper motion and was just this that allows us to obtain a convergence in our trace back and so the kinematic age. 

  • Daniel Baldomir added an answer:
    Why are there no stable states with more than three or less than two quarks?

    It is known that hadrons can be divided in baryons (fermions of three quarks) and mesons (bosons of two quarks). The sum of their electric charge is always an integer number, e.g. the proton is one and the neutron is zero. What is the reason that we have not found one particle with, say, five or seven quarks?

    Daniel Baldomir


    Thank you very much for your answer and sorry for my delay in responding. The application to cosmology is not obvious at all, but it seems that in the first moments previous to the hadron formation, around 10^(-35) seconds, i.e. in the inflationary age, it seems that the implications of having so massive particles could change the application of theorems as the of Borde-Vilenkin-Guth for singularities. I know that this far of my original question but it could help to understand a little better hypothesis as the dark matter, what do you think about?

  • Edgars Alksnis added an answer:
    How are the space and time related to biocentrism?
    Robert Lanza’s Biocentrism Theory
    Edgars Alksnis

    Space is as per Descartes/Newton; with time is a bit more complicated- but, believe, not in Your case.

  • G. Bothun added an answer:
    How is the tagging of photons from astronomical sources, done?

    How are the photons from different astronomical sources, which lie in the same solid angle from an observer, emitting in the same energy (i.e frequency or wavelength) region, tagged as coming from different sources? Does the Doppler shift play a vital role here? Or other techniques come in handy?

    G. Bothun

    If you just have fluxes through bandpass filters, the separation is difficult and model dependent as discussed.  If you can do integrated spectroscopy (often difficult) over the solid angle in question, you an do much better at resolving the individual components of the emission.

  • Russell Jurek added an answer:
    What is the limiting magnitude for detecting a galaxy in the SDSS image?

    See above

    Russell Jurek

    It's complicated by the fact that SDSS uses "luptitudes", instead of standard Pogson magnitudes. SDSS Luptitudes are designed to asymptote to fixed magnitude values. This avoids the weird magnitudes that you would otherwise get when you integrate noise.

  • Viacheslav Zgonnik added an answer:
    Looking for an advise on nebulae (molecular clouds, globules, protoplanetary disks)?

    Our group of geochemists, geologists and chemists is looking for a astrophysicists or astronomer who will be interested to participate in our research. We discovered the correlation between ionization potential of elements and their abundance in planets and other bodies. This correlation could be explained by a simple termochemical equation. Predictions by this equation correlate impressively well with observed chemical composition of surface of planets. We propose a theoretical process which could explain observed facts. Details of our work are described in this document
    We are looking for a person who could help us (in collaboration way) to improve and connect our theoretical model with observations of nebulae.

    Viacheslav Zgonnik

    It is correct. In our work we tested it on new data from space probes then interpreted the observed correlation as a Boltzmann distribution depending on the distance from the Sun. We tested our model on factual data for Moon, Mars, Venus and Meteorites. We find that predictions force of the model is excellent. Then, we made surface-to-volume analysis for elements. We find periodical trends, related with affinity of elements to hydrogen and with their mass. This suggests that radial differentiation of elements inside the planet was chemically- and gravity-driven. We have far more interesting results, which are out of scope of this paper.

  • Joseph L Alvarez added an answer:
    Radiation can lose energy by collisions with other particles. Does all radiation tend to end up being infrared radiation?
    The loss of energy results in an increase in wavelength for radiation. If the time this progress takes is infinitely long, could all radiation (gamma, x, UV, etc.) finish with a larger wavelength.
    Joseph L Alvarez

    Your question depends upon infinitely long. How and when we introduce infinity changes the results of a calculation. The result is a paradox if infinity is not properly introduced. A popular concept of entropy is that the entropy of a system increases. A closed, insulated system has constant entropy. When is it proper to introduce infinity in a closed system? Is the universe a closed system?

    Suppose we begin with the most intense gamma ray burst attainable. The gamma rays will lose energy with each interaction with matter or other photons (except for some exceptions noted in other answers). Nevertheless, if this gamma ray burst occurred at the beginning of the universe, at the current age of the universe, we still have a probability that some of the initial gammas have not interacted. Is this a case of improper use of infinity, even if the probability is ridiculously small?

    All the photons from the initial burst will have lost energy until some final gasp when that energy is absorbed in some process. We can say that the energy of the photons goes asymptotically to zero. So the answer to your question is that the photons degrade until they quietly absorb. That is the effect of carrying the equations to infinity.

    If the universe is a closed system and the entropy does not increase, do we require continuous bursts of intense gamma rays? Will the universe finally degrade to the average with a small distribution in energy? I do not believe there is an equation that will answer these questions, but there is an equation that says a burst of gamma rays will asymptotically degrade to zero.

  • Josep M. Trigo-Rodríguez added an answer:
    What is the source of neutral sodium in comets?

    Various authors have suggested sources in the dust tail, near the nucleus, in the plasma tail or some combination of all three (that might even turn off and on depending on what comet you are looking at at what time).

    Josep M. Trigo-Rodríguez

    The two previous readings suggested are excellent as they review nicely our knowledge on Na in comets. Let me point out that if the general scenario of comet formation is correct we should expect the accretion of significant amounts of Na in these bodies, perhaps in neutral form forming part of the interstitial matrix (also in ices?). Its presence could fit our detected overabundance of Na in cometary meteoroids that could be consequence of extensive Na depletion of the inner disk during the early solar system stage. See e.g. our paper:

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