A Guide on Observing the Sun
On 21st August 2017, one of the most photographed solar eclipses in history took place; in fact, the United States has finally been able to observe a total eclipse after more than 100 years since the last event. Thanks to this event, the attention on the Sun has grown exponentially and for this reason we decided to write an article that describes how to observe it.
The Sun is in fact a medium-sized star that is about 150,000,000 km away from Earth. Even from this enormous distance, we can perceive all its power, fuelled by the internal fusion of the nucleus. All this activity produces energy in the form of waves that we can study in white light or choose between different wavelengths, such as H-Alpha or Calcium.
White Light Filters
The white light filters reveal the bright face of the sun called the photo-sphere and the convective cells that move on its surface, which sometimes leave space to darker areas, called sunspots, which are colder regions. This type of filter provides a simple and inexpensive way to analyse the Sun, as it allows us to see daily and weekly changes in surface activity. If this is not enough, there is nothing more interesting than observing the Sun with an H-alpha filter (Hα). Looking at the eyepiece of a telescope with Hα filter you can see protuberances, flares and much more. Unlike the white light view, the H-alpha will show the true face of the Sun, e.g. a star in constant turmoil. You will never forget the first observation with a solar telescope and in the most active days, you may even notice a protuberance that grows in size and brightness right in front of your eyes!
The H-Alpha light is emitted by hydrogen atoms, by far the most common element in the Sun, when the electrons inside these atoms absorb energy and arrive at an energy level or greater orbit. When they then fall back into their original orbits, they release that energy in the form of light.
The process occurs with great efficiency in the solar atmosphere layer located just above the Fotosphere, called the Chromosphere. Here the temperature rises above 6000 ° C, hot enough to excite the hydrogen.
In some small telescopes, the etalon filters, pre-filtering and blocking can be in a different arrangement, but it does not matter, as everyone will only let H-alpha pass at the end. In addition to temperature controlled heaters for Doppler studies, small telescopes use a mechanical tilt mechanism or “pressure tuning” to vary the wavelength of red light.
The narrower the filter’s wavelength, the greater the contrast, all the crucial factors to see the details of the Chromosphere. A filter with a bandwidth of 0.7 to 0.5Å will show excellent details of the surface and the prominences. In contrast, those that transmit in the range from 0.9Å to 2Å will still offer a good view of the solar prominences, but the details of the disk will be difficult to detect due to the lower contrast.
Prices and Brands
The price of a small telescope dedicated exclusively to the H-alpha, starts at around £ 900 for a Coronado PST (Personal Solar Telescope), up to £ 14,000 for a Quantum SE standard 0.3S Daystar filter. If you are interested in buying, here is a list of companies that produce solar telescopes or filters:
Lunt Solar Systems: filters and telescopes in H-alpha
Coronado: filters and telescopes in H-alpha
Daystar filters: H-alpha filters and eyepieces
Baader Planetarium: filters only
What to watch?
What do you have to expect when you buy a solar filter or telescope? A lot! Surely you will immediately notice the protuberances that are quite frequent on our star.
The active protuberances are instead associated with diamonds and can be observed as shining informal boulders or, more rarely, as arches. If you look at one, do not stray too far from the telescope because you will see them change shape in real time. There will be no show that will leave you more amazed.
The protuberances can last for several days, which means that you can watch their changes even for a longer time, letting you reflect on the untiring activity of our star. The best time to observe them is surely when they approach the edge of the Sun, because thanks to the contrast with the dark sky, it will be much easier to identify them.
As for sunspots, their black nuclei seem similar to what is seen in white light, but in H-alpha, the penumbra extends into impressive vortices. When seeing is excellent, you will see strands and details in quantity.
The Sun will amaze you every time but many of its details will reveal themselves to the most tenacious observers over time. So, you just have to buy the most suitable equipment for you and start observing!