1.3j describe how astronomers observe the Sun at different wavelengths

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1 1.3j describe how astronomers observe the Sun at different wavelengths 1.3k demonstrate an understanding of the appearance of the Sun at different wavelengths of the electromagnetic spectrum, including visible, H-alpha, X-ray The emissions in each area of the electromagnetic spectrum are related to the temperature of the object. By observing the Sun at different wavelengths, a clearer view of events taking place can be seen across the whole spectrum. We see the surface of the Sun at 5,800K. At this temperature, the majority of the electromagnetic spectrum is released as visible light. Other parts of the electromagnetic spectrum should be weak emissions. However, the Sun is a powerful source of X-rays, which can only be produced at very high temperatures. Using telescopes to detect X-rays has allowed astronomers to understand what has produced the emissions and therefore given astronomers a better understanding of the Sun. Telescopes on Earth and in space have analysed emissions from the Sun over many years. Radio receivers like WAVES on the WIND satellite detect storms on the surface of the Sun (Coronal Mass Ejections CMEs). Infrared telescopes show cooler areas of the Sun as dark regions in images taken. The very successful EIT (Extreme ultra-violet Imaging Telescope) has taken amazing images of the chromosphere and low corona regions, when intense activity has been occuring. EIT forms part of SOHO (the SOlar and Heliospheric Observatory), the main observatory for viewing the Sun at different wavelengths. The observatory was launched on 2 nd December 1995 and contains a collection of 12 experiments to observe the activity of the Sun. Visible light observations allow details about sunspots, the solar wind and the corona to be studied. The biggest land solar telescope is the Dunn Solar Telescope at Sacramento Peak, New Mexico (seen on the left). The telescope is over 41 metres high above ground, but extends well into the ground (a further 67 metres). The telescope is on the leading edge of visible observations with two adaptive optics units, which in effect take out the wobble caused by the atmosphere. This gives much clearer imaging. The whole of the column of the telescope has a vacuum inside, to prevent distortion of the image due to convection currents which would be created by the extreme heat from the Sun. Picture credit : NSO/AURA/NSF One day, a 4m Advanced Technology Solar Telescope will be built in Hawaii.

2 Activity in the Solar Atmosphere (seen in visible light) SOLAR FLARES are violent eruptions, which occur when magnetic energy stored up in the complex magnetic field near a sunspot is suddenly released in a massive explosion. The flares will emit strong X-rays, ultraviolet light, visible light and solar wind. The amount of energy released is the equivalent of millions of 100 megaton hydrogen bombs exploding at the same time! The flares can last up to an hour and can affect events on the Earth if, as usually happens, the flare is associated with a coronal mass ejection. The biggest solar flares occur at, or near to, the solar maximum. Also, the extra activity can lead to the aurorae being seen in Britain. The next solar maximum will be around 2012, so we are beginning to see a rise in the Sun s activity again. A coronal mass ejection (CME) linked with a huge solar flare - seen in visible light

3 PROMINENCES are eruptions of gas into the chromosphere and corona. They are cooler than their surroundings, being between 10,000 K to 20,000 K. Usually, prominences are about a few times the size of the Earth. There are 2 types of prominences:- 1). Quiescent Prominences (Loop prominences) Loops of gas are trapped in the magnetic field around a pair of sunspots. These can erupt up to 50,000 km from the Sun s photosphere and last a few weeks. 2). Eruptive Prominences Similar to a very small flare, throwing material 500,000 km from the Sun.

4 HYDROGEN ALPHA (Hα) filters are commonly used to safely view the Sun. Viewing just the HYDROGEN ALPHA (Hα) wavelength of 656 nm and ignoring all the other wavelengths of light allows good views of solar flares, prominences, filaments (cooler strands over the disc of the Sun caused by prominences) and extra details of sunspot activity to be seen. Picture credit : Venturescope www telescopesales.co.uk The view of the Sun seen in HYDROGEN ALPHA (Hα). The surface features of the Sun are seen incredibly clearly. Picture credit : Pedro Ré Different appearances of the Sun with different filters As well as telescopes for individual astronomers and large observatories on Earth, satellites are in space, containing a range of instruments to study the Sun in different regions of the electromagnetic spectrum. SOHO has performed for much longer than expected. Hinode (meaning sunrise), is the more recent Japanese solar observatory.

5 Picture credit : NAOJ The range of telescopes can be seen on board the Hinode spacecraft. Hinode will use the X-ray telescope (XRT) to study the life cycle of solar magnetic field events. Telescopes studying X-rays have discovered details about the corona the atmosphere of the Sun. X-ray image of the Sun showing a solar flare in the corona and other regions of intense activity. Picture credit : NASA/GSFC and SOHO