My Science School

          Because of its extreme brightness, it is very dangerous to look at the Sun directly or through a telescope. Professional astronomers use tower telescopes to record the Sun’s activity. These are large telescopes with moving mirrors (heliostats) that reflect light down a long shaft to data-recording instruments on the ground.

          Unlike all the other stars in the Universe, which are very, very, very far away, our Sun is relatively close to the Earth (roughly 150 million km). The Sun is also quite large (about 1.5 million km in diameter) which allows us to see its visible surface as a round disk (about half-a-degree in diameter). The Sun extends far beyond this visible surface, but to see this outer component requires special equipment, often operating at non-visible wavelengths.

          The Sun gives off different kinds of energy: heat, visible light and invisible light. One invisible light that comes to Earth is called ultraviolet light. We're lucky that the Earth’s atmosphere protects us from most of the Sun’s UV, but some of it gets through and it is this UV light that can cause sunburn and eye damage. So, take care and protect yourself from the Sun!

          Wear sunscreen and stay in the shade when you can. Wear sunglasses on sunny days to protect your eyes from excessive UV. Never look directly at the Sun without the proper solar filters (NOT sunglasses)! Make a safe Sun-Earth Connection when you are outdoors.

          If properly protected, there are ways to look at the Sun. We can project it onto paper or even look at it through a telescope with solar filters. Solar events such as eclipses or transits (another planet passing in front of the Sun) are striking phenomena you won't want to miss, but you must carefully follow safety procedures. Don't let the requisite warnings scare you away from witnessing natural spectacles! You can experience the Sun safely, but it is vital that you protect your eyes at all times with the proper solar filters. No matter what recommended technique you use, do not stare continuously at the Sun. Take breaks and give your eyes a rest! Do not use sunglasses: they don't offer your eyes sufficient protection. 

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          The sun is constantly sending out a stream of charged particles into space, called the solar wind. The strength of the solar wind varies. It is usually at its strongest when the number of sunspots is highest. As these particles pass by Earth, some are trapped by the planet’s magnetic field, interacting with gases in the atmosphere. The reaction between particles and gases creates a multicoloured light-show that can be seen from Earth.

          Solar winds are geomagnetic storms that are formed by charged particles radiated by the outer atmosphere of the sun. These winds are said to develop within the center of the sun, which is a hot volatile core. All planets are protected from the sun's magnetic power by a magnetic field that deflects the power of the sun. The two effects of solar winds that manage to permeate the magnetic field are geo magnetic storms and disruption of communication and other satellites positioned in outer space.

          The solar winds ejected by the sun's corona or center are highly charged magnetic particles that travel through the atmosphere at 400 km per second. While each planet is protected by a magnetic field that deflects these charged volatile solar winds, the earth’s convenient position away from the sun is also a factor that keeps us protected from the ill effects of solar winds. Planets positioned closer to the sun experience considerable degeneration of the magnetic field through the power of solar winds.

          The effects of solar winds on the earth that are visible to naked eye are the Aurora Borealis (the Northern lights) at the North Pole and the Aurora Australis (he Southern Lights) at the South Pole. The fiery tail seen attached to comets is the effect of solar winds visible to the naked eye.

          We suffer the effects of solar winds on earth today because of the number of communication satellites in outer space. The magnetic field of solar distorts and even destroys the functioning of communication satellites. Astronauts and cosmonauts suffer serious radiation related health conditions if they are caught in the path of solar winds. Radiation from solar winds is known to cause chromosome damage and cancer, and these conditions may be fatal for humans in outer space. Radio and television communication and satellite based internet services are disrupted by solar winds. Military satellites are the affected the worst by solar winds. Geomagnetic storms caused by solar winds are very strong and can destabilize or destroy power grids. They also affect all navigation and communication systems especially for vessels at sea. Aircraft communications and instruments in the aircraft will be susceptible to faulty functioning during geomagnetic storms.

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          A solar eclipse occurs when the Moon comes directly between the Earth and the Sun. When this happens, the Sun’s light is blocked, and the Moon’s shadow falls on Earth. During an eclipse, the Moon and the Sun appear to be exactly the same size in the sky, because although the Moon is much smaller, it is also much closer. Total eclipses occur once every 18 months around our planet. However, it is estimated that any one place on Earth only sees a total eclipse every 360 years. An eclipse is when one celestial object moves in front of another one. There are two types of eclipses, solar and lunar.

Solar eclipses

          The Moon's shadow consists of two cone-shaped areas (see Figure 1), known as the umbra (externally tangent to the Sun and Moon) and the penumbra (internally tangent to the Sun and Moon). For an observer standing between the Moon and the umbra cone summit the eclipse is total. If the observer is beyond the cone summit, the eclipse is annular (ring-like): the apparent diameter of the Moon is too small to mask the whole solar disk. For an observer standing in the penumbra, only a part of the Sun is masked: the eclipse is partial.

          The most favourable conditions for a total eclipse are when the Moon is at its perigee, Earth is farthest from the Sun (around July) and when the Sun is observed near zenith. When these conditions are all met, one can have totality duration of more than seven minutes.

Lunar eclipse

          A lunar eclipse occurs when Earth comes between the Sun and the Moon. This phenomenon can be seen by any observer on Earth for whom the Moon is above the horizon, and so is much more frequent. Lunar eclipses occur at the time of a Full Moon, and when the Moon is near one of the nodes of intersection between its orbit and the ecliptic plane.

          Earth's umbra is larger than the whole Moon. So, one will observe either a total eclipse by the umbra (which can be well observed), a partial eclipse by the umbra and penumbra, or a total or partial eclipse by the penumbra only. The duration of a lunar eclipse is much longer than a solar eclipse, and can take as much as six hours.

          In practice, the lunar eclipse conditions are modified due to the refraction of the Sun's rays by Earth's atmosphere. This refraction (of 35 minutes of arc) allows some light to penetrate the cone of geometric umbra. So even during total lunar eclipse, the lunar disk is not completely dark. This grazing light is more absorbed by Earth's atmosphere in the blue and yellow portions of the spectrum, giving a particular reddish light during total lunar eclipse.

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          The sun is a large ball of gas. It is so large that, if it was hollow, one million Earth-sized planets could fit inside it! Sun is the largest and the most massive object in the solar system, but it is just a medium-sized star among the hundreds of billions of stars in the Milky Way galaxy.

          The sun is nearly a perfect sphere. Its equatorial diameter and its polar diameter differ by only 6.2 miles (10 km). The mean radius of the sun is 432,450 miles (696,000 kilometers), which makes its diameter about 864,938 miles (1.392 million km). You could line up 109 Earths across the face of the sun. The sun's circumference is about 2,713,406 miles (4,366,813 km). It may be the biggest thing in this neighborhood, but the sun is just average compared to other stars. Betelgeuse, a red giant, is about 700 times bigger than the sun and about 14,000 times brighter.

          We have found stars that are 100 times bigger in diameter than our sun. "We have also seen stars that are just a tenth the size of our sun.” It's possible that the sun is even larger than previously thought. Xavier Jubier, an engineer and solar eclipse researcher, creates detailed models of solar and lunar eclipses to determine precisely where the moon's shadow would fall during the solar eclipse. But when he matched actual photos and historical observations with the models, he found precise eclipse shapes only made sense if he scaled up the sun's radius by a few hundred kilometers.

          Even missions like NASA's Solar Dynamics Observatory (SDO) and measurements of the inner planets across the face of the sun don't refine the star's radius as precisely as desired. "It's harder than you think just to put a ruler on these images and figure out how big the sun is — [SDO] doesn't have enough precision to nail this down," NASA researcher Ernie Wright told Space. com. "Similarly, with the Mercury and Venus transits, it turns out [a measurement based on those is] not quite as precise as you'd like it to be."

          Wright said different papers using a variety of methods have produced results that differ by as much as 930 miles (1,500 km). That could be a problem if you are planning to skirt the edges of the next solar eclipse.

          "For most people, yes, it doesn't really matter; it won't change everything," Jubier said. "But the closer you get to the edge of the [eclipse] path, the more risk you take."

          Sunquakes are violent eruptions on the Sun around areas of hot gas. These explosions send out shockwaves more powerful than the detonation of a billion tonnes of high explosives.

          Earthquakes start deep below the surface, when two blocks of the crust suddenly slips, releasing enormous amounts of energy. The motion creates seismic waves that ripple throughout our planet. There are quakes on the Sun as well. But they originate above the surface, in giant outbursts of magnetic energy.

          As the Sun rotates, it produces a strong magnetic field. Over time, the lines of magnetic force become tangled and twisted. Those lines occasionally snap, creating explosions of energy or geysers of charged particles. These outbursts originate above the Sun’s visible surface, and they direct most of their energy outward. But some of it is directed back toward the Sun. That heats particles in the Sun’s lower atmosphere, creating a pressure wave that penetrates deep into the Sun. The wave then reflects back to the surface, causing a “Sunquakes.” Hot gas ripples outward from the site of the quake, and seismic waves travel deep into the Sun.

          As you might expect, Sunquakes are massive events — they can be thousands of times more powerful than the deadly quake that struck Japan a couple of years ago. And like earthquakes, they can reveal what’s going on below the surface. The sound waves reverberate throughout the Sun and reflect back to the surface, causing it to jiggle. Astronomers can measure these jiggles and use them to probe conditions below the surface — thanks to the power of Sunquakes.

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          The surface of the sun often appears to be dotted with small dark patches. These are called sunspots. They form when the Sun’s magnetic field blocks the heat rising from inside the Sun. Sunspots are actually very bright but appear dark because of their surroundings.

          The surface of the Sun is a very busy place. It has electrically charged gases that generate areas of powerful magnetic forces. These areas are called magnetic fields. The Sun’s gases are constantly moving, which tangles, stretches and twists the magnetic fields. This motion creates a lot of activity on the Sun's surface, called solar activity. Sometimes the Sun’s surface is very active. Other times, things are a bit quieter. The amount of solar activity changes with the stages in the solar cycle. Solar activity can have effects here on Earth, so scientists closely monitor solar activity every day.

          Sunspots are areas that appear dark on the surface of the Sun. They appear dark because they are cooler than other parts of the Sun’s surface. The temperature of a sunspot is still very hot though—around 6,500 degrees Fahrenheit!

          Why sunspots are relatively cool? It’s because they form at areas where magnetic fields are particularly strong. These magnetic fields are so strong that they keep some of the heat within the Sun from reaching the surface. The magnetic field lines near sunspots often tangle, cross, and reorganize. This can cause a sudden explosion of energy called a solar flare. Solar flares release a lot of radiation into space. If a solar flare is very intense, the radiation it releases can interfere with our radio communications here on Earth. Solar flares are sometimes accompanied by a coronal mass ejection (CME for short). CMEs are huge bubbles of radiation and particles from the Sun. They explode into space at very high speed when the Sun’s magnetic field lines suddenly reorganize.

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