Astronomical objects give off electromagnetic waves.   We are able to detect some of these waves as light, but most of them are invisible to us.   Waves of different lengths can do very different things. 

The visible spectrum formed by sunlight on a CD

Very short waves can be used to see if you've broken a bone, a bit longer and they can give you sunburn, longer still and you can see them.   Make them even longer and you can barbeque with them, a bit longer and you can use them to heat up food in seconds.  Once the waves are over 1cm long they can be used to send television and radio programmes.

The electromagnetic spectrum

A great deal of information comes to us from astronomical objects in the form of electromagnetic waves.  Generally the hotter an object is, the shorter the electromagnetic wavelength it gives off.   Human eyes can only sense a tiny portion of the spectrum of these waves as visible light: between about 400 and 700nm (billionths of a metre).   One reason for this is that most parts of the EM spectrum are filtered out by the Earth's atmosphere.   However there is a window that coincides with the visible range.  Your eyes have evolved to look through that window.

White-light filters and projection devices like the 'Sunspotter' show us a mixture of visible wavelengths, revealing some of the features of the Sun's photosphere such as sunspots.   On top of the photosphere is a layer called the chromosphere. Here great tendrils of flaming hydrogen burst out into space or arch over and plunge back into the Sun.   The excited hydrogen atoms in these flares and prominences send out a signature wavelength of red light, called hydrogen alpha, at exactly 656.3nm .   Unfortunately their light is swamped by the brilliant underlying photosphere.   Luckily special filters can filter out most of the photosphere spectrum, leaving only the hydrogen alpha light and revealing the spectacular chromosphere in all its glory.

Other wavelengths reveal different aspects of the Sun's structure.   The SOHO space observatory is able to sense the short wavelengths of the extreme ultraviolet part of the electromagnetic spectrum which is given off when parts of the Sun get really violent .   Beyond ultra violet there are x-rays which are also given off by the Sun.   The next generation of solar space telescopes like SOLARB are aiming to explore the x-ray region of the E.M. spectrum in detail.

For a fantastic poster and booklet (2Mb PDF) on our 'Multiwavelength Universe' click here

The graphic below shows some of the views of the Sun given by Our Star* instruments. 1nm is a billionth of a metre or 10^-9m.   Our forthcoming portable radio telescopes will enable you to extend your range of observations far beyond the red end of the visible spectrum.

More details of the EM spectrum at NASAs Goddard Space Flight Centre 'Imagine the Universe'

And a great pdf(2Mb) booklet on observations through the spectrum from NASAs Space Link

Near-real-time images in many parts of the EM spectrum are on this page