Do you have friends, relatives or business partners all over the world and in different time zones? In this case probably it is important for you to know the daylight period all over the world. On World and City Map's daylight maps you can find out if this is the right time to call them, or it is better not to.
Daylight Saving Time (or summer time as it is called in many countries) is a way of getting more light out of the day by advancing clocks by one hour during the summer. During Daylight Saving Time, the sun appears to rise one hour later in the morning, when people are usually asleep anyway, and sets one hour later in the evening, seeming to stretch the day longer.
Daylight Saving Time Explained
Daylight saving is a summertime adjustment to the local time in a country or region, designed to cause a higher proportion of its citizens’ waking hours to pass during daylight. To follow the system, timepieces are advanced by an hour on a pre-decided date in spring and reverted back in the fall. About half of the world’s nations use daylight saving.
The reason DST works is because its saves energy due to less artificial light needed during the evening hours - clocks are set one hour ahead during the spring, and one hour back to standard time in the autumn. Many countries observe DST, and many do not.
Note: Between March - April through September - November, it is summer in the northern hemisphere, where many countries may observe DST, while in the southern hemisphere it is winter. During the rest of the year the opposite is true: it is winter in the northern hemisphere and summer in the southern.
Why We Have Daylight Saving Time
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Google's interactive daylight map
The decrease in daylight during the winter months is due to Earth's axial tilt of 23 degrees. If the Earth was not tilted on its axis, the length of day and night would remain steady year long. During winter in the northern hemisphere there are less daylight hours, and the southern hemisphere in turn has longer daylight hours and experiences summer.
The Solar System
Nine major planets, their satellites, and countless minor planets (asteroids) orbit the Sun to form the Solar System. The Sun, our nearest star, creates energy from nuclear reactions deep within its interior, providing all the light and heat which make life on Earth possible. The Earth is unique in the Solar System in that it supports life: its size, gravitational pull and distance from the Sun have all created the optimum conditions for the evolution of life.
Diameter: 864,948 miles (1,392,000 km)
Mass: 1990 million million million million
The Sun was formed when a swirling cloud of dust and gas contracted, pulling matter into its center. When the temperature at the center rose to 1,000,000°C (1,800,000°F), nuclear fusion – the fusing of hydrogen into helium, creating energy – occurred, releasing a constant stream of heat and light.
The formation of the Solar System
The cloud of dust and gas thrown out by the Sun during its formation cooled to form the Solar System. The smaller planets nearest the Sun are formed of minerals and metals. The outer planets were formed at lower temperatures, and consist of swirling clouds of gases.
A solar eclipse occurs when the Moon passes between Earth and the Sun, casting its shadow on Earth’s surface. During a total eclipse, viewers along a strip of Earth’s surface, called the area of totality, see the Sun totally blotted out for a short time, as the umbra (Moon’s full shadow) sweeps over them. Outside this area is a larger one, where the Sun appears only partly obscured, as the penumbra (partial shadow) passes over.
The Incoming Energy From The Sun
The Earth receives energy from the Sun. This is termed "insolation". Earth must return this energy back to space if it is not to heat up. But the Earth is rotating; during the daytime it receives energy and during the night it can radiate this energy back into space. The Earth is also nearly spherical, so that most of the energy received from the sun is around the equator, where the sun is overhead. In the polar regions the sun is close to the horizon in summer and below the horizon in winter, so there the energy can be more effectively radiated back into space.
If the Earth were just a giant rock, the side facing the sun would become very hot during the day and very cold at night. Earth’s moon is just such an object. Its average distance from the sun is the same as the Earth’s. However, the day length of the moon is 29.5 Earth days (about 709 h). During the day the average temperature of the moon’s surface is 107 °C (=225 °F), and where the sun is directly overhead the temperature reaches 123 °C (=253 °F), well above the boiling point of water on Earth. During the lunar night the average surface temperature drops to −153 °C (=−243 °F) with some areas falling to −233 °C (=−387 °F). These troubling facts escaped the producers of the 1984 film 2010—The Year we Make Contact which shows the comfortable accommodations of our colony on the Moon. If the Earth were just a rock, it would also experience day-night temperature extremes, although they would be somewhat less because Earth’s day length is 24 h, so that during the day there would be less time for the heat to build up and at night less time for the heat to dissipate. The greatest diurnal temperature ranges recorded at the Earth’s surface are in the Sahara (50 °C = 90 °F) and Siberia (67 °C = 120 °F). In the tropics, the night-day temperature range can be as small as 1 °C (=1.8 °F).
Fortunately, the Earth is not just a rock. Two fluids cover it: liquid water (the ocean, seas and lakes), and a mixture of gases (the atmosphere). These fluids can circulate, and they redistribute the heat to reduce temperature contrasts on the Earth’s surface. Some of the gases in the atmosphere absorb and reradiate energy. Transitions between the three phases of H2O, ice, water, and vapor play a large role in redistribution of energy on the Earth.
The incoming energy from the sun is in the form of “short wave” radiation. Earth dissipates this back into space as “long wave” radiation, shown in Fig. 10.3. To determine how much and what wavelengths of radiation will be emitted by an object, physics uses Stefans’s Fourth Power Law and Kirchhoff’s “black body” concept. Remember that a black body is a hypothetical construct, it is an object that absorbs all the electromagnetic energy that falls onto it and transmits none of that energy. It is an ideal source of thermal radiation. In the real world there are no perfect "black body radiators", but the sun and the tungsten filament in an electric light bulb come close. If the temperature of an object is below about 700 K (427 °C = 800 °F), the wavelengths emitted by it cannot be sensed by the human eye, and it appears black. However, if the object has a higher temperature we see it as colored. The sun has a surface temperature of about 5778 K (= 5,505 °C = 9,941 °F). Most of the energy received from the sun is in that part of the electromagnetic spectrum we call ‘light’, which ranges from shorter wavelengths we call violet or blue, to the longer wavelengths we call red, as shown in Fig. 10.3. Some of the radiation is of even shorter wavelengths, the ultraviolet, and some is in longer wavelengths, the near infrared. Human eyes have evolved to be sensitive to the most intense radiation from the sun. We cannot sense ultraviolet, probably because most of it does not reach the Earth’s surface. We can sense the infrared, which we feel as warmth or heat.
If you read the labels on light bulbs or do much color photography, you are already familiar with this temperature- radiation effect. Particularly, when you replace your incandescent bulbs with the fluorescent or LED bulbs that use much less energy, you will find the color of the light emitted by the bulb described as some temperature Kelvin. For a warm candlelight feel you want about 4,000 K, for a daylight effect you want 5,700 K, of course, and for garish blue-white light you want 7,000 K. There are some good sites on the web that will show you what the color of the light emitted from the bulb will be. In fluorescent bulbs, it is not a heated filament that emits the light; the fluorescent bulb is no ‘black body’ but uses a wholly different principle to emit light—that’s why it uses so much less energy and why it doesn’t get hot. You can even buy fluorescent bulbs that will work with a dimmer. Their color temperature stays almost the same as they are dimmed; they just emit less light. If you dim an incandescent light bulb it goes from white to orange to red.
The total energy received each year by Earth will change if the luminosity of the Sun changes. If the Sun emits more energy, the Earth must warm. Unfortunately we have only a very brief direct history of changes in solar radiance. The question sometimes arises - could our Sun be a variable star, with large changes in its energy output over time? The "variable stars" astronomers speak of change in brightness over periods of hours to days to a few years. We do not have a long enough astronomical record to know how they might vary over centennial or longer timescales.
On the other hand, we do know about variations in our Sun’s radiance on decadal and centennial time scales from direct evidence. There are also some indications that it may vary on thousand-year time scales. Finally, there are climatic variations on millennial time scales that are attributed to the Sun without any real evidence for a link.
Our Sun is a variable star, with sunspots appearing and disappearing on a roughly 11 year cycle. The Sun radiates more energy when sunspots are present than when they are not. This is because "faculae", bright spots among the dark sunspots, more than make up for the lowered radiation from the spots. The change in insolation between sunspot maxima and minima is about 0.5 W/m2, a difference of less than 0.1 %.
There have been periods when there were no sunspots for several decades. The most recent of these was the Maunder Minimum which lasted from about 1645 to 1710. The Maunder Minimum coincided with an especially cold phase of the "Little Ice Age" and it has been suggested that diminished insolation may have been the cause although other possibilities have been proposed recently. Other attempts to relate sunspot activity to global climate, wine vintages, and economics have proven inconclusive.
Satellite observations since 1978 have documented solar variability with a precision previously unknown and have shown that while the variations of the visible spectrum with sunspot cycle are very small they may be as much as 50 % in the ultraviolet.
Solar storms are events on the Sun that produce flares and eject matter from its corona. The solar storm of 1859, known as the Carrington Flare, disrupted the then new telegraph lines and other electrical devices.
Cosmic rays are actually highly energetic particles, about 90 % protons, and the rest mostly helium nuclei, traveling at very high speeds. They come from outside our solar system. They can be deflected by particles streaming out from the Sun’s outer atmosphere, the corona, that form the solar wind. The strength of the solar wind varies with the sunspot cycle, and induces an 11 year cycle in cosmic ray intensity. As they approach the Earth, the cosmic ray particles can also be deflected by the Earth’s magnetic field.
In the 1930s it was discovered that cosmic rays produce showers of subatomic particles into the lower part of the atmosphere. These air showers are the result of the impact of highly energetic incoming particles with molecules in the upper atmosphere. Billions of exotic short-lived particles are produced in these collisions and rain down into the lower levels of the atmosphere. The investigation of cosmic rays and the advent of high energy particle accelerators after WWII led to the discovery of new kinds of subatomic particles: more kinds of muons, pions, kaons and neutrinos. At present there are more than 25 kinds of subatomic objects in the ‘particle zoo.’
Two of the byproducts of cosmic ray interactions are carbon-14 and beryllium-10. Carbon-14 is formed from nitrogen-14 as one of the protons in its nucleus is replaced by a neutron. It has a half life of 5,730 years and has been widely used for dating materials back to 20,000 years; more recently, with the improved technology of accelerator mass spectrometry, back to 60,000 years. Carbon-14 dating is complicated by the fact that the rate of its production in the upper atmosphere varies with time and because of contamination of the atmospheric reservoir by ‘dead’ carbon introduced by burning fossil fuels. These problems have been overcome for the younger part of the record by comparing carbon-14 dates with tree ring ages.
Beryllium-10 is a spallation product produced by cosmic ray particles splitting atoms in the molecules of the air or materials in the ground. It has a half life of about 1.5 million years, and has been used to determine the changes in the rate of carbon-14 production in the upper atmosphere.
There has been speculation that the ionization of air molecules by cosmic rays may serve to create nucleation sites for water droplets and influence cloud formation, and thus impact Earth’s climate. This speculation was very popular for a brief period during the late 1990s and early 2000s. The evidence for correlations has not stood up to careful examination.
The energy from the interior of the Earth is only about one fourth of a percent of the insolation, much too small to have any effect on climate.
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