Observing and imaging the Sun safely

This page has been on the site since 2004 and has been rewritten for current equipment and the solar cycle as it stands now.

The Sun is the one astronomical object you can observe from a city backyard at lunchtime. It is also the only one that can blind you in a fraction of a second. Every part of solar observing starts with that fact.

The one rule

Never look at the Sun through unfiltered binoculars, a telescope, a finder scope or a camera viewfinder. Optics concentrate sunlight, and the damage to the retina is painless, quick and permanent. Cap or remove the finder scope before you start, and never leave a telescope unattended where children could look through it.

White-light filters

The standard approach for a small telescope is a full-aperture solar filter that fits securely over the front of the tube. Good ones use glass or polymer film from established solar filter makers and block all but a tiny fraction of the light, along with harmful infrared and ultraviolet. Points to check:

• The filter covers the whole front opening and cannot blow off in a gust. Tape it on if in doubt.
• Inspect it before every session. Hold it up to a bright lamp: any pinhole or scratch means replace it.
• Avoid the old screw-in eyepiece "sun filters" sold with some cheap telescopes. They sit at the focus, heat up and can crack without warning.

For eye viewing without a telescope, use eclipse glasses certified to ISO 12312-2, and never combine them with binoculars or a telescope.

Projection

Projection lets a group watch together. A small refractor or binoculars (one side capped) can throw an image of the Sun onto white card held behind the eyepiece. Keep people away from the eyepiece, do not use expensive cemented eyepieces, which can be damaged by heat, and never let the projecting instrument point at the Sun unattended.

Even simpler is pinhole projection: a small hole in card throws an image of the Sun onto paper a metre or so behind it. During a partial eclipse, the gaps between leaves do the same, scattering crescents over the ground. A small mirror with most of its surface masked off can bounce a Sun image onto a shaded wall, which is a lovely way to show a classroom an eclipse.

Hydrogen-alpha telescopes

Dedicated hydrogen-alpha telescopes pass a very narrow slice of deep red light at 656.3 nanometres. Through one, the Sun becomes a living thing: prominences on the limb, dark filaments across the disc, bright active regions. They are expensive, but many astronomy societies own one and bring it to public events. A RASNZ affiliated society near you is the best way to try one before buying.

Sunspots and the solar cycle

Sunspots are cooler, magnetically active regions that look dark against the bright photosphere. Their numbers rise and fall over roughly 11 years. Solar Cycle 25 reached its maximum around 2024 to 2025, and the Sun is now in the slow decline, though big spots and strong flares still turn up for years after a peak. Those active regions also drive the auroras that reach New Zealand skies.

Counting spots and sketching their positions over several days is a satisfying project. You will see the Sun rotate, about once every 27 days as seen from Earth, and watch groups grow and decay.

Imaging basics

With a proper front filter in place, the Sun is a bright target:

• Use fast shutter speeds and low ISO; the problem is too much light, not too little.
• Focus on the sharp edge of the disc or on a sunspot.
• Shoot early in the morning, before the ground heats up and the air turns wobbly.
• Short video clips, stacked with free software, beat single frames for sharpness.

NASA keeps an excellent overview of our star, its structure and current missions on its Sun pages.