Focus your sights on the Sun
Sunspots are temporary regions of intense magnetic disturbance on the Sun’s surface, where the energy from below is blocked by magnetic forces. This causes the area to cool down slightly compared to the surrounding surface, creating the dark sunspots visible to observers.
When looking at a sunspot, you will notice two distinct parts: a nearly black area called the ‘umbra’ (there may be several if the sunspot is extensive), and a much lighter region called the “penumbra” surrounding the umbra.
Sunspots can occur individually, but they often appear in groups, which are then classified into sunspot types depending on their extent and structure. The number, size, and structure of sunspots vary over an average 11-year cycle known as the Sunspot Cycle.
- At Sunspot Minimum, there are usually few or no sunspots for many days or even weeks.
- Gradually, the number of sunspots begins to rise, and their sizes increase.
- After about three or four years, we usually reach Sunspot Maximum, when the Sun is rarely without some sunspots visible.
- This situation persists for about two or three years, after which the intensity of sunspots starts to decrease over the remaining years until we are back at Sunspot Minimum.
Dedicated amateur observers record observations of the total number of sunspots and groups each month, allowing them to create graphs showing the rise and fall of sunspot activity. Recent observations have shown that not all Sunspot Maxima are equal in intensity. Cycle 24, which started in 2008, was of lower intensity than the two preceding cycles, while Cycle 25, according to recent forecasts, has already hit its maximum or will do so very soon.
Another useful observation is the position of sunspots on the solar disk, which can be plotted using a solar latitude and longitude system. By plotting these positions against time, observers can produce a beautiful graph called a “Butterfly Diagram,” named for its resemblance to the wings of a butterfly.
There are several techniques for observing sunspots and other solar features, ranging from simple and inexpensive methods to more advanced setups. One of the easiest ways to view sunspots is through solar projection.
To project the Sun’s image, insert an inexpensive eyepiece into your telescope and cap the finder (if present) to avoid damaging your better eyepieces with the Sun’s heat. Without looking through the telescope, aim it towards the Sun by watching the shadow of the tube on the ground. When the shadow is smallest, a fuzzy bright spot should appear within it.
Hold a piece of white paper or card about 20 centimeters behind the eyepiece to catch the bright spot. Gently focus the telescope until the projected image is sharp, and move the paper or card away from the eyepiece to make the image larger. You should be able to see at least one or two sunspots on the bright solar disk.
For a more permanent setup, you can attach an adjustable screen or box to the telescope to catch the projected image. However, avoid using this method with plastic or mirror-based telescopes, as the Sun’s heat can damage them.
An alternative to projection is the use of full-aperture solar filters that fit securely over the front of the telescope. These filters block all but a tiny proportion of the Sun’s light, allowing safe observation. You can choose between film-like coated filters or glass-coated filters, both of which must meet stringent safety standards and be inspected before each use.
- Film-like coated filters are more affordable but easier to damage, so they require thorough checking before use.
- Glass-coated filters are more expensive but slightly more robust, though they still need to be checked before every use.
For the best views of sunspots, consider using a Herschel Wedge, a device named after Sir John Herschel, who invented it. The Herschel Wedge can only be used at the eyepiece end of a refractor (lens) telescope and reflects a small percentage of the Sun’s energy towards the eyepiece while refracting the rest, including infrared and ultraviolet radiation, away from the observer.
While providing excellent views of sunspots, the Herschel Wedge is more expensive than a full-aperture filter and cannot be used on telescopes larger than 150mm aperture due to potential overheating. Manufacturers’ instructions must be followed carefully when using a Herschel Wedge.
