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    Sunspot Experiments

    Sunspot Background

    Definition

    A sunspot is an area of high magnetic activity on the surface of the Sun.

    Basics

    Sunspots produce bright light, but not as much as the surface around them, so they appear dark by comparison. They are cooler than the rest of the sun. Some are small, and some are ten times bigger than Earth.

    Chinese astronomers said they could see sunspots. On 17 March 1802 the monk Adelmus saw a big sunspot, which he could see for eight days. Adelmus thought that Mercury was going in front of the Sun and making a black spot. However, they didn't really know what sunspots were until Galileo Galilei said a right explanation in 1612.

    Sunspots were important when people wondered if the sun rotated, because they could see that sunspots changed.

    The first cyclic changes of sunspots was seen by Heinrich Schwabe, and made Rudolf Wolf study them carefully, starting in 1848. Also in 1848, Joseph Henry showed a picture of the Sun and made sure that sunspots were cooler than the rest of the sun (they are about 4500 degrees). They are still very hot, but much cooler than the rest of the outside part of the sun.

    Sunspots are cooler than the rest of the sun, but many scientists think that when there are a lot of sunspots, the sun actually gets hotter. This affects the weather here on Earth, and also radio reception. Without sunspots the earth would probably be cooler. In the same way, if there were too many sunspots, the earth would get really hot, and there would not be a lot of rain. This would make lots of droughts on the Earth. Droughts are a long time with no rain. When it doesn't rain, the plants die: when the plants die, many animals die too. People need rain to live. The food we eat can't grow without a lot of rain. A drought can be a very dangerous thing. The sunspots help keep Earth the right temperature. Scientists study sunspots and other solarphenomena, so they can know what they do to Earth. A sunspot cycle of eleven years has been found, with changes in activity.

    Topics of Interest

    Sunspots are temporary phenomena on the surface of the Sun (the photosphere) that appear visibly as dark spots compared to surrounding regions. They are caused by intense magnetic activity, which inhibits convection, forming areas of reduced surface temperature. Although they are at temperatures of roughly 3,000–4,500 K, the contrast with the surrounding material at about 5,780 K leaves them clearly visible as dark spots, as the intensity of a heated black body (closely approximated by the photosphere) is a function of T (temperature) to the fourth power. If a sunspot were isolated from the surrounding photosphere it would be brighter than an electric arc. Sunspots expand and contract as they move across the surface of the sun and can be as large as 80,000 km (50,000 miles) in diameter, making the larger ones visible from Earth without the aid of a telescope.

    The manifestation of intense magnetic activity, sunspots host secondary phenomena such as coronal loops and reconnection events. Most solar flares and coronal mass ejections originate in magnetically active regions around visible sunspot groupings. Similar phenomena indirectly observed on stars are commonly called starspots and both light and dark spots have been measured.

    Solar variations refer here to changes in the amount of total solar radiation and its spectral distribution. There are periodic components to these variations, the principal one being the 11-year solar cycle (or sunspot cycle), as well as aperiodic fluctuations. Solar activity has been measured by satellites during recent decades and estimated using 'proxy' variables in prior times. Scientists studying climate change are interested in understanding the effects of variations in the total and spectral solar irradiance on the Earth and its climate.

    The solar storm of 1859, also known as the Solar Superstorm, or the Carrington Event, was the most powerful solar storm in recorded history.

    The solar cycle, or the solar magnetic activity cycle, is the main source of periodic solar variation driving variations in space weather. The cycle is observed by counting the frequency and placement of sunspots visible on the Sun. Powered by a hydromagnetic dynamo process driven by the inductive action of internal solar flows, the solar cycle.

    Radio propagation describes how radio waves behave when they are transmitted, or are propagated from one point on the Earth to another. Like light waves, radio waves are affected by the phenomena of reflection, refraction, diffraction, absorption, polarization and scattering.

    Radio propagation is affected by the daily changes of ionization in the atmosphere, due to the Sun. Understanding the effects of varying conditions on radio propagation has many practical applications, from choosing frequencies for international shortwave broadcasters, to designing reliable mobile telephone systems, to radio navigation, to operation of radar systems. Radio propagation is also affected by several other factors determined by its path from point to point. This path can be a direct line of sight path or an over-the-horizon path aided by refraction in the ionosphere. Factors influencing ionospheric radio signal propagation can include sporadic-E, spread-F, solar flares (occur in active regions around sunspots), geomagnetic storms, ionospheric layer tilts, and solar proton events.

    The Wolf number (also known as the International sunspot number, relative sunspot number, or Zürich number) is a quantity which measures the number of sunspots and groups of sunspots present on the surface of the sun.

    A solar flare is a large explosion in the Sun's atmosphere that can release as much as 6 × 1025 joules of energy. The term is also used to refer to similar phenomena in other stars, where the term stellar flare applies.

    Solar flares affect all layers of the solar atmosphere (photosphere, corona, and chromosphere), heating plasma to tens of millions of kelvins and accelerating electrons, protons, and heavier ions to near the speed of light. They produce radiation across the electromagnetic spectrum at all wavelengths, from radio waves to gamma rays. Most flares occur in active regions around sunspots, where intense magnetic fields penetrate the photosphere to link the corona to the solar interior. Flares are powered by the sudden (timescales of minutes to tens of minutes) release of magnetic energy stored in the corona. If a solar flare is exceptionally powerful, it can cause coronal mass ejections.

    Source: Wikipedia (All text is available under the terms of the GNU Free Documentation License and Creative Commons Attribution-ShareAlike License.)

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