DOCSLIB.ORG

Phase Steps and Amplitude Fading of VLF Signals at Dawn and Dusk D

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Phase Steps and Amplitude Fading of VLF Signals at Dawn and Dusk D RADIO SCIENCE Journal of Research NBS/USNC-URSI Vol. 69D, No. 11, November 1965 Phase Steps and Amplitude Fading of VLF Signals at Dawn and Dusk D. Walker Ministry of Aviation, Royal Aircraft Establishment, S. Farnborough, Hampshire, England (Received March 12, 1965; revi sed June 28, ]965) An experiment is described which tests the consequences of an explanation by Crombie of phase steps and amplitude fading at dawn and dusk. It is concluded that the ex planation is valid at 18.0 kc/s for the types of path studied. 1. Introduction 120 The diurnal phase variation of VLF signals over l' ( 0) N BA - NAIROBI ,..., long paths is generally in the form of a trapezium ,.... >< <1l IZS50 ~m 0 [Pierce, 1955] where all night conditions over the [( J- - a.... path correspond to one steady-phase level, and all day 80 - 4: ~ OJ -' conditions over the path correspond to the other steady­ w -3 c uJ 0 phase level. The idealized transition from one phase uJ :> level to the other during dawn and dusk completes the 'fl 40 -12 30 t: :r -' 0. a.. straight sides of the trapezium, and this paper dis­ -' ~ « 20 "- cusses deviations from this in the form of phase steps z ;i, '";n z during the transition period. The phase steps are 10 0 ";n accompanied by signal fading, and this had in fact been noticed before trans mitter frequencies were stable 0 enough to detect the diurnal phase variations [Ander­ 00 04 OB 12 1& 20 >4 son, 1928]. Attempts were made to explain the ampli­ 1IME,U1 tude fading by Yokoyama and Tanimura [1933] and the phase steps by Rieker [1963]. Both explaniltions 100 - were based on single-ray geometrical optics, but it has 1 been pointed out by 13udden [1961] and Wait [1962a] ,..., >< ,.... 0 t that many rays are needed to explain VLF propagation dl 0: over very long paths. Crombie [1964] put forward J.- 110 a.... " an explanation based on the use of modes in the earth­ ~ ~'" w-' w ionosphere waveguide in which two modes are present c 0 ...:> in the nighttime part of the path and only one mode in :M :; <; a. daylight. He s howed that this explanation fitted most iE ~ -' 4: of the observed facts and that it had consequences z4: -' :i which were capable of verification by further experi­ '"on 0 30 <.!J mental evidence. on An experiment is described in this paper which :00 produced results in support of Crombie's explanation. The experiment involved the use of a mobile monitor 00 04 OB 12 16 20 24 TIME)UT station on board ship, and a permanent ground moni­ tor station, both of which recorded the phase and FIGURE 1. NBA 18.0-kc/s phase (cp) and amplitude (A) records, amplitude of NBA 18.0-kc/s signals from Balboa, 6 December 1963. Canal Zone. The consequences of Crombie's explanation are studied in more detail, and it is shown that the dif- ference in phase velocity and the differ. ence in attenu­ 2. Explanation of Phase Steps Put Forward I ation rate for the two lowest order modes at night can by Crombie be deduced from experimental data. Information can also be obtained on the transmitter Phase steps and signal fading similar to that illus­ excitation factor and the mode conversion at the trated in figure 1 were studied by Crombie [1964] ionosphere discontinuity. on the transmissions of NPM (19.8 kc/s), Hawaii, to 1435 781-7000- 65 - 4 Boulder, Colo., and NBA (18.0 kc/s), Canal Zone, to the nighttime height of ionosphere which determines Frankfurt, Germany. He noted that: the two mode velocities, and hence the distance moved (1) The rapid change of phase took place at the same by the dawn-dusk line between minima). However, time as the amplitude minimum; the experimental evidence in support of the simul­ (2) the rapid phase change was in the direction of taneity of the minimum signal at sunrise was slight, decreasing phase delay during sunrise, and of increas· and none was available to show that at sunset the inter­ ing phase delay during sunset (i.e., in the same ference pattern moves with the sunset line. Thus direction as the general phase change at these times); the explanation, while fitting the general facts, had (3) during sunrise, the deepest minimum occurred not been verified by any substantial amount of experi- , latest in time, i. e., with the dawn line closest to the mental evidence. transmitter, but during sunset the evidence from the The principal object of this paper is to describe an two paths was not so definite; experiment in which the main consequences of (4) NPM signals received at Boulder and at Wash· Crombie's explanation have been verified. The ington (almost on a great·circle line from Hawaii) experiment is described in section 3, and the analysis seemed to show that the minima during sunrise oc· of the results is discussed in section 4. curred at the same time at the two places, to within The consequences of the explanation by Crombie 5 min or less (only a few days' observations were are discussed more fully by taking into account the available); and transmitter excitation factor, the mode conversion (5) the distance moved by the dawn·dusk line along coefficient at the dawn-dusk discontinuity, and the the transmitter-receiver paths between times of signal attenuation rates of the first two waveguide modes. minima was the same for sunrise and sunset. None of these factors were considered in detail by Crombie put forward a model similar to that illus­ Crombie. The relationships derived are applied to trated in figure 2 to explain the observations. He the experimental data in section 4 to give the difference assumed that at sunrise, for a west-to-east trans­ in phase velocity and the difference in attenuation mission, two waveguide modes are present in the dark rate for the first two modes at night. By assuming a part of the path between the transmitter and the dawn theoretical value for the excitation factors of mode 1 discontinuity, but that at the discontinuity the second and mode 2 at night, an estimate is made of the ratio mode is converted to first mode, so that no second of the two lowest order mode conversion coefficients mode exists in the daylight part of the path. He at the dawn discontinuity. showed that the consequences of these assumptions are that when destructive interference takes place to 3. Experimental Data give a voltage minimum, the rapid phase change is The two main consequences of Crombie's explana­ in the observed direction, and that all points to the tion of the dawn-dusk phase steps are that, for a W -to·E east of the dawn discontinuity should experience the path, signal minimum simultaneously, which agrees with (1) At dawn, all points to the east of the discontinuity the few days' observations quoted above. should experience the signal minima simultaneously; In order to explain the sunset phenomena, Crombie (2) at dusk, the interference pattern should be on assumed that only the first waveguide mode exists the dark side of the discontinuity and should move between the transmitter and the discontinuity, but with the discontinuity so that the time of occurrence that some second mode is generated at the discon­ of minimum signal should depend on the location of tinuity, so that between this point and the receiver, the receiver. in the dark part of the path, two modes are present, The verification of both of these results could be and an interference pattern is formed which moves done ideally by placing a large number of receivers westward with the sunset line. Crombie showed at intervals along a great-circle path from a suitable that with this model, the rapid phase change associated transmitter, and simultaneoulsy recording the phase with the voltage minimum is again in the observed and amplitude of the signal at all the points. This direction. experiment was not feasible, but a permanent record­ Crombie's model therefore fitted observations (1), ing station at a great distance from a transmitter, (2), (4), and (5) (the latter, since in each case it is together with a mobile ' recording station moving to a different position each day along the great-circle path between the transmitter and the permanent monitor station, is a good approximation to the ideal, and this experiment has been done. dN d01 r- --1 A permanent monitor station is in operation at the MODEl "----+ IONOSPHERE+---....Y MODE I I University of East Africa, Nairobi, Kenya, and the + + MODEl MODEl MODEZ phase of received VLF signals is compared with the IV\OOE.~ phase derived from a rubidium-vapor frequency ........-:;-;NI"'GH""T-------,D""'A77V -l'" GROUND .......'NlliIG""H"'"T------,Q<\'"'"""V- ........ standard. The phase difference is recorded together TRAN5MITTER RECEIVER TRANSMITT ER RECEIVER with signal amplitude, and the phenomenon of phase .) SUNRISE b) SUNSET steps and amplitude fading can be seen clearly on the NBA 18.0-kc/s records, an example of which is given FIGURE 2. Ionosphere model for sunrise and sunset. in figure la. The path length is 12,950 km. The 1436 FIGURE 3. Path followed by H.M.S. Vidal dluin~ ExerciJe Navado. dawn steps are always very noticeable, the number made between 30 October and 21 December 1963, varying between four and seven but those at dusk are produced good quality VLF data, and this has been much less pronounced and are sometimes masked used in the subsequent analysis. The path of the by locally generated noise.
Load more

Recommended publications
  • View and Print This Publication
    @ SOUTHWEST FOREST SERVICE Forest and R U. S.DEPARTMENT OF AGRICULTURE P.0. BOX 245, BERKELEY, CALIFORNIA 94701 Experime Computation of times of sunrise, sunset, and twilight in or near mountainous terrain Bill 6. Ryan Times of sunrise and sunset at specific mountain- ous locations often are important influences on for- estry operations. The change of heating of slopes and terrain at sunrise and sunset affects temperature, air density, and wind. The times of the changes in heat- ing are related to the times of reversal of slope and valley flows, surfacing of strong winds aloft, and the USDA Forest Service penetration inland of the sea breeze. The times when Research NO& PSW- 322 these meteorological reactions occur must be known 1977 if we are to predict fire behavior, smolce dispersion and trajectory, fallout patterns of airborne seeding and spraying, and prescribed burn results. ICnowledge of times of different levels of illumination, such as the beginning and ending of twilight, is necessary for scheduling operations or recreational endeavors that require natural light. The times of sunrise, sunset, and twilight at any particular location depend on such factors as latitude, longitude, time of year, elevation, and heights of the surrounding terrain. Use of the tables (such as The 1 Air Almanac1) to determine times is inconvenient Ryan, Bill C. because each table is applicable to only one location. 1977. Computation of times of sunrise, sunset, and hvilight in or near mountainous tersain. USDA Different tables are needed for each location and Forest Serv. Res. Note PSW-322, 4 p. Pacific corrections must then be made to the tables to ac- Southwest Forest and Range Exp.
    [Show full text]
  • VHF and UHF Signal Characteristics Observed on a Long Knife-Edge Diffraction Path A
    JOURNAL OF RESEARCH of the National Bureau of Standards- D. Radio Propagatior. Vol. 65D, No. 5, September- Odober 1961 VHF and UHF Signal Characteristics Observed on a Long Knife-Edge Diffraction Path A. P. Barsis and R. S. Kirby (R eceived April 6, 1961) Contribution from Central Radio Propagation Laboratory, National Bureau of Standards, Boulder, Colo. During 1959 and 1960 long-term transmission loss measurements were performed over a 223 kilom eter path in Eastern Colorado using frequencies of 100 and 751 megacycles per second. This path intersects P ikes P eak which forms a knife-edge type obstacle visible from both terminals. The transmission loss measurements have been analyzed in terms of diurnal a nd seaso nal variations in hourly medians and in instan taneous levels. As expected, results show t hat the long-term fading range is substantially less t han expected for t ropospheric seatter paths of comparable length. T ransmission loss levels were in general agreem ent wi t h predicted k ni fe-edge d iffraction propagation when a ll owance is made for rounding of t he knife edge. A technique for est imatin g long-term fading ra nges is presented a nd t he res ults are in good agreement with observations. Short-term variations in some case resemble t he space-wave fadeo uts commonly observed on within- the-horizon paths, a lthough other phe­ nomena may contribute to t he fadin g. Since t he foreground telTain was rough there was no evidence of direct a nd grou nd-refl ected lobe structure.
    [Show full text]
  • Capacity of Flat and Freq.-Selective Fading Channels Linear Digital Modulation Review
    Lecture 8 - EE 359: Wireless Communications - Winter 2020 Capacity of Flat and Freq.-Selective Fading Channels Linear Digital Modulation Review Lecture Outline • Channel Inversion with Fixed Rate Transmission • Comparison of Fading Channel Capacity under Different Schemes • Capacity of Frequency Selective Fading Channels • Review of Linear Digital Modulation • Performance of Linear Modulation in AWGN 1. Channel Inversion with Fixed Rate Transmission • Suboptimal transmission strategy where fading is inverted to maintain constant re- ceived SNR. • Simplifies system design and is used in CDMA systems for power control. • Capacity with channel inversion greatly reduced over that with optimal adaptation (capacity equals zero in Rayleigh fading). • Truncated inversion: performance greatly improved by inverting above a cutoff γ0. 2. Comparison of Fading Channel Capacity under Different Schemes: • Fading generally decreases channel capacity. • Rate/power adaptation have similar capacity as rate adaptation alone. • Rate adaptation alone has same capacity as no adaptation (RX CSI only) but rate adaptation is more practical due to complexity of ML decoding over long blocklengths that experience all fading values. This ML decoding is necesssary to achieve capacity in the RX CSI only case. • Truncated channel inversion is more practical than rate adaptation, with significant capacity gain over full channel inversion, which has zero capacity in Rayleigh fading. 3. Capacity of Frequency Selective Fading Channels • Capacity for time-invariant frequency-selective fading channels is a \water-filling” of power over frequency. • For time-varying ISI channels, capacity is unknown in general. Approximate by di- viding up the bandwidth subbands of width equal to the coherence bandwidth (same premise as multicarrier modulation) with independent fading in each subband.
    [Show full text]
  • Distortion Exponent of Parallel Fading Channels
    Distortion Exponent of Parallel Fading Channels Deniz Gunduz, Elza Erkip Department of Electrical and Computer Engineering, Polytechnic University, Brooklyn, NY 11201, USA [email protected], [email protected] Abstract— We consider the end-to-end distortion achieved by the fading process. Lack of channel state information at the transmitting a continuous amplitude source over M parallel, transmitter prevents the design of a channel code that achieves independent quasi-static fading channels. We analyze the high the instantaneous channel capacity and requires a code that SNR expected distortion behavior characterized by the distortion exponent. We first give an upper bound for the distortion performs well on the average. We aim to design a joint source- exponent in terms of the bandwidth ratio between the channel channel code that achieves the minimum expected end-to-end and the source assuming the availability of the channel state distortion. Our main focus is the high SNR behavior of this information at the transmitter. Then we propose joint source- expected distortion (ED). This behavior is characterized by the channel coding schemes based on layered source coding and distortion exponent denoted by ¢ and defined as multiple rate channel coding. We show that the upper bound is tight for large and small bandwidth ratios. For the rest, we log ED provide the best known distortion exponents in the literature. ¢ = ¡ lim : (1) SNR!1 log SNR By suitably scaling the bandwidth ratio, our results would also apply to block fading channels. When we consider digital transmission strategies that first compress the source and then transmit over the channel at I.
    [Show full text]
  • The Golden Hour Refers to the Hour Before Sunset and After Sunrise
    TheThe GoldenGolden HourHour The Golden Hour refers to the hour before sunset and after sunrise. Photographers agree that some of the very best times of day to take photos are during these hours. During the Golden Hours, the atmosphere is often permeated with breathtaking light that adds ambiance and interest to any scene. There can be spectacular variations of colors and hues ranging from subtle to dramatic. Even simple subjects take on an added glow. During the Golden Hours, take photos when the opportunity presents itself because light changes quickly and then fades away. 07:14:09 a.m. 07:15:48 a.m. Photographed about 60 seconds after previous photo. The look of a scene can vary greatly when taken at different times of the day. Scene photographed midday Scene photographed early morning SampleSample GoldenGolden HourHour photosphotos Top Tips for taking photos during the Golden Hours Arrive on the scene early to take test shots and adjust camera settings. Set camera to matrix or center-weighted metering. Use small apertures for maximizing depth-of-field. Select the lowest possible ISO. Set white balance to daylight or sunny day. When lighting is low, use a tripod with either a timed shutter release (self-timer) or a shutter release cable or remote. Taking photos during the Golden Hours When photographing the sun Don't stare into the sun, or hold the camera lens towards it for a very long time. Meter for the sky but don't include the sun itself. Composition tips: The horizon line should be above or below the center of the scene.
    [Show full text]
  • On Routing in Random Rayleigh Fading Networks Martin Haenggi, Senior Member, IEEE
    IEEE TRANSACTIONS ON WIRELESS COMMUNICATIONS, VOL. 4, NO. 4, JULY 2005 1553 On Routing in Random Rayleigh Fading Networks Martin Haenggi, Senior Member, IEEE Abstract—This paper addresses the routing problem for large loss probabilities increase with the number of hops (unless the wireless networks of randomly distributed nodes with Rayleigh transmit power is adapted). fading channels. First, we establish that the distances between To overcome some of these limitations of the “disk model,” neighboring nodes in a Poisson point process follow a generalized Rayleigh distribution. Based on this result, it is then shown that, we employ a simple Rayleigh fading link model that relates given an end-to-end packet delivery probability (as a quality of transmit power, large-scale path loss, and the success of a service requirement), the energy benefits of routing over many transmission. The end-to-end packet delivery probability over short hops are significantly smaller than for deterministic network a multihop route is the product of the link-level reception models that are based on the geometric disk abstraction. If the probabilities. permissible delay for short-hop routing and long-hop routing is the same, it turns out that routing over fewer but longer hops may While fading has been considered in the context of packet even outperform nearest-neighbor routing, in particular for high networks [16], [17], its impact on the network (and higher) end-to-end delivery probabilities. layers is largely an open problem. This paper attempts to shed Index Terms—Ad hoc networks, communication systems, fading some light on this cross-layer issue by analyzing the perfor- channels, Poisson processes, probability, routing.
    [Show full text]
  • Kahn Communications, Inc. 425 Merrick Avenue Westbury, New York 11590 (516) 2222221
    KAHN COMMUNICATIONS, INC. 425 MERRICK AVENUE WESTBURY, NEW YORK 11590 (516) 2222221 THE "WGAS EFFECT" AND THE FUTURE OF AM RADIO In the history of broadcasting a number of "Effects" have dramatically impacted on broadcasting. For example, the "Capture Effect" and the "Multipath Effect" of FM, and earlier "Radio Luxemburg Effect" helped shape broadcasting history. More recently, "Clicks and Pops", "Platform Motion", and "Rain Noise" have influenced the path of AM Stereo. Remember when the Magnavox system was selected by the FCC as the standard in 1980 and the "Click and Pop" effect was discovered. By 1982 it became clear that this "Click and Pop" problem made it essential that the FCC revisit its decision. There is now a new phenomenon which we propose to name the "WGAS Effect" because it was first described in the "Open Mike" section of the September 7, 1987 issue of "Broadcasting" by Mr. Glenn Mace, President of WGAS, South Gastonia, North Carolina. It is essential that all AM broadcasters carefully read this short letter because the very future of AM radio may depend upon the industries knowledge of its contents. It should be stressed that WGAS does not, and cannot, endorse our stereo system as they have never used it. But, nevertheless, we are most appreciative that Mr. Mace has taken the time and effort to make his observations public on this important matter. More will follow re the "WGAS Effect" and how it impacts on all stations, large and small, which must serve listeners in their 25 my/meter contour and beyond. age.
    [Show full text]
  • Planit! User Guide
    ALL-IN-ONE PLANNING APP FOR LANDSCAPE PHOTOGRAPHERS QUICK USER GUIDES The Sun and the Moon Rise and Set The Rise and Set page shows the 1 time of the sunrise, sunset, moonrise, and moonset on a day as A sunrise always happens before a The azimuth of the Sun or the well as their azimuth. Moon is shown as thick color sunset on the same day. However, on lines on the map . some days, the moonset could take place before the moonrise within the Confused about which line same day. On those days, we might 3 means what? Just look at the show either the next day’s moonset or colors of the icons and lines. the previous day’s moonrise Within the app, everything depending on the current time. In any related to the Sun is in orange. case, the left one is always moonrise Everything related to the Moon and the right one is always moonset. is in blue. Sunrise: a lighter orange Sunset: a darker orange Moonrise: a lighter blue 2 Moonset: a darker blue 4 You may see a little superscript “+1” or “1-” to some of the moonrise or moonset times. The “+1” or “1-” sign means the event happens on the next day or the previous day, respectively. Perpetual Day and Perpetual Night This is a very short day ( If further north, there is no Sometimes there is no sunrise only 2 hours) in Iceland. sunrise or sunset. or sunset for a given day. It is called the perpetual day when the Sun never sets, or perpetual night when the Sun never rises.
    [Show full text]
  • Ozone: Twilit Skies, and (Exo-)Planet Transits
    Astronomical Science Ozone: Twilit Skies, and (Exo-)planet Transits Robert Fosbury1 the atmosphere, can be rich and varied. This article is about the effect of ozone George Koch 2 The processes that result in this palette on the colour of the twilit sky and, in the Johannes Koch 2 are geometrically complex, but comprise same vein, its appearance as the strong- a limited number of now well-understood est telluric absorption feature in the visi- physical effects. This understanding was ble spectrum of the Earth as it would be 1 ESO not gained easily. From the time when seen by a distant observer watching it 2 Lycée Français Jean Renoir, München, early humans first consciously posed the transit in front of the Sun. We present and Germany question: “What makes the sky blue?”, to analyse spectrophotometric observations the time when the processes of scatter- of sunset and also discuss observations ing by molecules and molecular density of the eclipsed Moon reported by Pallé et Although only a trace constituent gas fluctuations were elucidated, thousands al. (2009). in the Earth’s atmosphere, ozone plays of years passed, during which increas- a critical role in protecting the Earth’s ingly intensive experiments and theories surface from receiving a damaging flux were developed and carried out (Pesic, Ozone of solar ultraviolet radiation. What is not 2005). generally appreciated, however, is that Ozone (O3 or trioxygen) is an unstable the intrinsically weak, visible Chappuis Most physicists, if asked why the sky is allotrope of oxygen that most people can absorption band becomes an important blue, would answer with little hesitation: detect by smell at concentrations as influence on the colour of the entire sky “Because of Rayleigh scattering by mole­ low as 0.01 parts per million (ppm).
    [Show full text]
  • Long-Wave and Medium-Wave Propagation
    ~EMGINEERING TRAINING SUPPLEMENT No. 10 LONG-WAVE AND MEDIUM-WAVE PROPAGATION BRITISH BROADCASTING CORPORATION LONDON 1957 ENGINEERING TRAINING SUPPLEMENT No. 10 LONG-WAVE AND MEDIUM-WAVE PROPAGATION Prepared by the Engineering Training Department from an original manuscript by H. E. FARROW, Grad.1.E.E. Issued by THE BBC ENGINEERING TRAINING DEPARTMENT 1957 ACKNOWLEDGMENTS Fig. 2 is based upon a curve given by H. P. Williams in 'Antenna Theory and Design', published by Sir Isaac Pitrnan and Sons Ltd. Figs. 5, 6, 7, 8 and 9 are based upon curves prepared by the C.C.I.R. CONTENTS ACKNOWLEDGMENTS... ... INTRODUCTION ... ... ... AERIALS ... ... ... ... GROUND-WAVEPROPAGATION ... GEOLOGICALCORRELATION ... PROPAGATIONCURVES ... ... RECOVERYAND LOSS EFFECTS ... MIXED-PATHPROPAGATION ... SYNCHRONISED. GROUP WORKING LOW-POWERINSTALLATIONS ... IONOSPHERICREFLECTION ... FADING ... ... ... ... REDUCTIONOF SERVICEAREA BY SKYWAVE ... LONG-RANGEINTERFERENCE BY SKYWAVE ... APPENDIXI ... ... ... ... ... REFERENCES ... ... ... ... ... LONG-WAVE AND MEDIUM-WAVE PROPAGATION The general purpose of this Supplement is to explain the main features of propagation at low and medium frequencies i.e. 30-3000 kc/s, and in particular in the bands used for broadcasting viz. 150-285 kc/s and 525-1605 kc/s. In these bands, the signal at the receiver may have two components: they are (a) a ground wave, i.e. one that follows ground contours (b) an ionspheric wave (sky wave) which is reflected from an ionised layer under certain conditions. In the vicinity of the transmitter, the ground wave is the predominant component, and for domestic broadcasting, the service ideally would be provided by the ground wave only. In fact the limit to the service area is often set by interference from the sky wave.
    [Show full text]
  • Evening Or Morning: When Does the Biblical Day Begin?
    Andrews University Seminary Studies, Vol. 46, No. 2, 201-214. Copyright © 2008 Andrews University Press. EVENING OR MORNING: WHEN DOES THE BIBLICAL DAY BEGIN? J. AM A ND A MCGUIRE Berrien Springs, Michigan Introduction There has been significant debate over when the biblical day begins. Certain biblical texts seem to indicate that the day begins in the morning and others that it begins in the evening. Scholars long believed that the day began at sunset, according to Jewish tradition. Jews begin their religious holidays in the evening,1 and the biblical text mandates that the two most important religious feasts, the Passover2 and the Day of Atonement,3 begin at sunset. However, in recent years, many scholars have begun to favor a different view: the day begins in the morning at sunrise. Although it may be somewhat foreign to the ancient Hebrew mind to rigidly define the day as a twenty-four-hour period that always begins and ends at the same time,4 the controversy has important implications for the modern reader. The question arises: When does the Sabbath begin and end? The purpose of this paper is to examine whether the day begins in the morning or in the evening by analyzing the sequence of events on the first day of creation (Gen 1:2-5), examining texts that are used to support both theories, and then determining how the evidence in these texts relates to the religious observances prescribed in the Torah. Because of time constraints, I do not explore the question of whether or not the days in Gen 1 are literal.
    [Show full text]
  • Driving at Dawn and Dusk According to Research, There Is an Increased Risk to Safety Whilst Driving During Civil Twilight
    Driving at Dawn and Dusk According to research, there is an increased risk to safety whilst driving during civil twilight. Read our guide for tips on driving safely at Dawn and Dusk. www.kinto-uk.com 0333 222 0966 Factsheet: Driving at Dawn and Dusk – Version: 1.0 Driving at Dawn and Dusk The period just before sunrise (dawn) or right after sunset (dusk) is called civil twilight, when the sky is still bright but you can’t see the sun. It is considered as a dangerous time for driving because the light in the sky prevents the eyes to adjust to the dark road. Furthermore, the glare from the sunset/sunrise can further interfere with your vision and last but not least, during these hours drivers are more likely to be drowsy. Here we outline some of the tips to keep you and others safe on the road: 1. Keep windscreen and all other windows clean in order to ensure clarity. Dust and dirt can reflect light which can further affect you vision. 2. Keep your lights on so other vehicles can see you. 3. Reduce speed and avoid tailgating. By doing so, you will have more time to react if an emergency occurs or the vehicle in front of you stops suddenly. 4. Stay alert and be cautious for cyclists, pedestrians and other road users. At these times driver tiredness is also common. 5. Avoid distractions such as using your mobile phone, changing radio stations or trying to eat/drink. 6. Use your sun visor to help you shade your eyes from the sunlight glare.
    [Show full text]