The Solar Scout

Observing the Sun with the Skywatcher’s solar telescope

The solar scout in action in my backyard (Credit: Southerly Goës).

By Dirk Goës

Warning

Never look directly at the Sun as it will result in permanent damage to your eyesight.  It is never safe to look directly at the Sun, a partial solar eclipse or the partial phases of a total solar eclipse without the proper equipment and techniques.  For more information on viewing the Sun safely see this informative webpage from the Astronomical Society of Australia. 

Introduction

As we head towards the total solar eclipse that will occur on the 22nd of July 2028, now is a great time to learn more about our home star and how to safely observe it.  The total solar eclipse will track right across Australia from the Kimberley Region in Western Australia to directly across Sydney.  For more information on the total solar eclipse, you can refer to the excellent website published by the Astronomical Society of Australia. 

The Sydney City Skywatchers (SCS) have an important history of solar observations and research that was conducted by Harry Roberts and Monty Leventhal OAM.  Janette Brennan, the editor of the SCS Astronomers' Bulletin often includes one of their archival articles. 

SCS owns a ‘Daystar Solar Scout 60mm Solar Telescope’ for use at club outreach and viewing events.  This article provides an overview of the telescope and what features of the Sun you may be able to observe.  The Daystar Solar Scout filters light from the Sun at one particular wavelength called H-alpha and this article describes what H-alpha is and why it is a useful wavelength for observing features of the Sun.  However, this article is not an instruction manual for the telescope and the best way to learn how to use it is to attend one of the club’s viewing events. 

The solar telescope and tracking mount

As well as the 60 mm dedicated solar telescope the kit includes a ‘SolarQuest’ tracking mount.  This battery powered device finds the Sun automatically and rotates the telescope to the correct position and then keeps the Sun in view by continually tracking its position.  It does this via combination of GPS and a finder scope.  The telescope itself also requires a power source that keeps the H-alpha filter at the required temperature.  There is a tuning knob which allows for small adjustments to the filtered wavelength by up to 0.5 Angstroms (0.05 nanometres). 

The kit comes with a Powertech rechargeable battery pack, cables, a diagonal and a tripod.  If you are familiar with setting up telescopes of various kinds you will find it straightforward, if you are new to telescopes there will be some new concepts to learn.  The main components of the telescope are shown in figure 1 and 2 below. 

Figure 1: The Solar Scout telescope and the SolarQuest tracking mount all set up and ready to use (Credit: Dirk Goës).

Figure 2: The full setup of the telescope showing the SolarQuest tracking mount and H-alpha filter connected to the PowerTech battery pack.  The SolarQuest can also be run with 8 AA-batteries but inserting and removing the battery cassette is difficult and fiddly (Credit: Dirk Goës). 

What can you see?

The Sun appears as a red disk through the telescope.  I have been able to see dark sunspots on the disk and prominences on the limb of the Sun.  The prominences look like red whiffs of cloud coming off the side (limb) of the Sun, often curling like a breaking wave.  Other times they might look like smoke rising from a bushfire or smoke from an erupting volcano.  They are quite spectacular, especially when you think about how big these curtains of ionised gas really are.  Probably much bigger than the Earth. 

I have not been able to see other features that the telescope manual claims you can view such as granulation, spicules, filaments or flares.  However, this is probably partly due to a lack of experience and that I have been using the telescope in summer where the warm ground can transmit interfering radiation.  I only have one eyepiece which is a 40 mm Plössl that Ann Cairns lent to me.  The manual for the telescope recommends Plössl eyepieces of size 25 mm, 32 mm and 40 mm.  It would be good to try some of the other sizes. 

A good way to check and understand what you are seeing through the telescope is to compare your observations against the images on the Australian Space Weather Forecasting Centre website.  The website includes a H-alpha image of the Sun that is updated every 60 seconds as shown in figure 3. 

Figure 3: A H-alpha image of the Sun from the Learmonth solar observatory in Western Australia (Credit: Learmonth Solar Observatory). 

Viewing the Sun in H-alpha

It is safe to view the Sun through the Solar Scout Telescope as it filters out the bright glaring light from the Sun and only allows through red light at the specific wavelength of 656.3 nanometres (nm).  This wavelength is known as H-alpha because hydrogen atoms in the Sun’s atmosphere either absorb or emit photons of light at this exact wavelength.  Whether a photon of light is absorbed or emitted depends on the current energy level of a hydrogen atoms electron. 

Figure 4: The spectrum of visible light showing four of the wavelengths that indicate the presence of hydrogen.  A H-alpha telescope filters in light with a specific wavelength of 656.3 nanometres (nm).  The visible spectrum ranges from 400 to 700 nm (Diagram: Dirk Goës).

When viewing the Sun at the H-alpha wavelength we are seeing light from the Sun’s chromosphere which is the middle layer of the Sun’s atmosphere above the photosphere and below the corona.  At this wavelength it is possible to see many features such as sunspots, filaments, granulation on the Sun’s surface and prominences on the Sun’s limb. 

Figure 5: A schematic diagram showing the different layers of the Sun, their approximate temperatures and the type of spectrum they produce.  Note that the actual solar spectrums show thousands of absorption and emission lines from the many elements present in the Sun.  Temperatures are in Kelvin (K), subtract 273 to get Celsius (Diagram: Dirk Goës). 

The bright glaring light from the Sun that lights up and warms our planet comes from the Sun’s photosphere (‘Sphere of light’).  The photosphere is the first and densest layer of the Sun’s atmosphere directly above the Sun’s interior.  If you view the Sun through a H-alpha telescope it blocks out the light from the photosphere and allows you to see light from the chromosphere, the second layer of the Sun’s atmosphere.  To understand why this occurs you need to understand a little about spectroscopy, the science of breaking light into a spectrum and studying its features. 

If you heat up a solid object to a high enough temperature, like a bar of iron, it will start to glow.  If you capture this light and break it up into a spectrum it will appear as a rainbow with each colour transitioning smoothly into the next.  The interior of the Sun, a dense gas, behaves exactly like a heated solid object and produces an uninterrupted rainbow spectrum.  This type of spectrum is called a continuous spectrum. 

The photosphere, the first layer of the Sun’s atmosphere directly above the interior, produces a different kind of spectrum called an absorption spectrum.  An absorption spectrum is punctuated by dark lines at very specific wavelengths which represent the presence of different elements such as hydrogen and helium.  Absorption lines occur when energetic photons of light from a hot object move through a cooler gas.  The atoms which make up this cooler gas such as hydrogen and helium absorb these energetic photons at specific wavelengths and therefore create dark lines in the spectrum. 

The photosphere is much cooler than the interior of the Sun and therefore produces an absorption spectrum.  Specifically for our purposes hydrogen atoms in the photosphere absorb photons of light at a wavelength of exactly 656.3 nm.  In effect the photosphere produces no light at the H-alpha wavelength of 656.3 nm.  This is why a H-alpha telescope can block out the bright glaring light of the photosphere. 

The chromosphere, the layer of the Sun’s atmosphere above the photosphere, produces a different kind of spectrum again, called an emission spectrum.  An emission spectrum displays bright lines at very specific wavelengths which, like an absorption spectrum, represent the presence of different elements such as hydrogen and helium.  Emission lines occur in a hot gas as electrons in atoms of elements like hydrogen and helium loose energy and emit photons of light at specific wavelengths. 

The chromosphere is a hot gas that is much hotter than the photosphere below it.  Therefore, it produces an emission spectrum.  Specifically for our purposes hydrogen atoms in the chromosphere emit photons of light at a wavelength of exactly 656.3 nm.  The chromosphere strongly emits light at the H-alpha wavelength of 656.3 nm.  This is the light we are seeing through a H-alpha telescope. 

The outermost layer of the Sun’s atmosphere is the very thin but extremely hot corona.  It has a complex spectrum that is mainly visible in ultraviolet light and therefore does not show up in a H-alpha telescope.  The best time to view the corona is during a total solar eclipse. 

It may seem counterintuitive that the temperature of the Sun’s atmosphere increases as you go up through the layers.  While it is beyond the scope of this article it is related to the Sun’s chaotic magnetic field breaking through the Sun’s surface and magnetically heating the layers above. 

Viewing the Sun safely

The safest way to view the Sun is through a dedicated solar telescope such as the Skywatcher’s Solar Telescope described in this article.  It is also possible to attach solar filters of various kinds to a regular nighttime telescope.  However, this requires more care to ensure that you do not look through the eyepiece without first correctly attaching the filter. 

The Sun can also be viewed safely through dedicated solar eclipse glasses.  For more information on viewing the Sun safely see this webpage from the Astronomical Society of Australia. 

Thanks to Ann Cairns for showing me how to set up and use the Skywatcher’s Solar Telescope. 

The telescope manuals can be found at the following links:

Skywatcher SolarQuest Tracking mount

Daystar Solar Scout Telescope