How to observe and track sunspots

By Pete Lawrence

Published: Friday, 01 April 2022 at 12:00 am

In this guide we’ll reveal how to monitor solar activity by observing sunspots, focussing on a particular group and noting how they move or change on the Sun’s surface over time.

The Sun exhibits a visual activity cycle, a solar cycle, where it goes from displaying few if any sunspots, before ramping up in numbers to a point where there is a regular procession of spot groups across the Sun’s Earth-facing hemisphere.

The time taken for the spot group numbers to go from minimum to maximum, and back to minimum again, is approximately 11 years.

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Solar activity over cycles 22-24
Credit: David Hathaway, NASA, Marshall Space Flight Center

We’re currently in the build-up to a maximum, with the peak of Solar Cycle 25 expected around 2025.

As sunspot groups are now reasonably common, a good challenge is to follow one or more groups on a daily basis, monitoring for changes.

The Sun rotates differentially, its equatorial rotation being 25 days, and the rotation in its polar regions being 35 days.

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When you create a sequence of sunspot images, make sure your setup is correctly aligned to capture the changes in activity. Credit: Pete Lawrence

Sunspot groups appear at the eastern limb and appear to move across the Sun’s disc on a path parallel to the solar equator, which itself may appear tilted north, south or be presented sideways on to us.

Sunspot observations can be done using a telescope with the correct filters. The most common option is to cover the entire aperture of the scope with a certified white-light filter.

However, sunspot monitoring can also be done with narrowband filters such as hydrogen-alpha (Ha) and calcium-K (Ca-K).

For more on solar filters, read our guides on how to observe the Sun and how to photograph the Sun.

You should never observe or image the Sun with the naked eye or any unfiltered optical instrument.

Finding then tracking sunspots

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AR2577 by Ewan Hobbs, Hastings, UK. Equipment: AZEQ6 GT Skywatcher Mount, TecnoSky 152mm Refractor, Daystar Quark Chromosphere, Baader 135mm D-ERF & Point Grey IMX 174 camera.

Finding a spot on the limb can be a matter of being lucky with timing and the weather. Often you’ll be picking up your first view of a spot after it has rotated well onto the disc.

Once found, sketch or image the spot on as many days as possible, and maintain the same equipment setup between sessions.

If you manage to grab a number of results you can animate them together.

For sketches, scan each one into a computer and use an animation-capable software to make a flick-book sequence.

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Sun Spot AR2645 by Mark Forbes, Stockport, UK. Equipment: Altair Astro StarWave 102 ED f/7 refractor, Altair Astro IMX174 mono Hypercam, Daystar Quark Chromosphere filter.

With each observation, make a note of the date, time and orientation of the view.

Programs such as WinJUPOS and TiltingSun can help. The Gong H-alpha network is another great repository, which will show you current activity.

To keep your Sun images aligned with one another, orientate the camera so that when slewing an equatorial mount in RA (Right ascension), features move parallel to the base of the imaging frame.

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Solar Activity by Alastair Woodward, Derby, UK. Equipment: Sky-watcher 120mm Evostar Achromat Refractor, Daystar Quark Chromosphere, Point Grey Blackfly mono CMOS

Programs such as TiltingSun can assist with the orientation of altazimuth mounted setups.

The weather can play havoc with an observational sequence like this and it may take many attempts to get a run of daily results.

Achieving a 12–13 day run across the disc may seem impossible at times. However, as ever in astronomy, persistence and tenacity are the key to success.

If you do manage to observe or image sunspots, let us know by sending us your images or get in touch via Facebook, Twitter or Instagram. 

This guide originally appeared in the April 2022 issue of BBC Sky at Night Magazine.