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Guidelines for Solar Observers

Solar observing is unique among the objects that AAVSO observers pursue because it is so bright. The most important guideline for solar observing is observe safely. This cannot be stressed enough, and if you are uncertain about any of the following equipment and safety recommendations, please request assistance before making any observations of the Sun with your equipment.

Safety and equipment guidelines

  • Do not look directly at the sun without the protection offered by a filter. For naked eye viewing, a piece of #14 welder's glass provides adequate protection. Do not use overexposed film, dark glasses, or other media that are not designed specifically for solar viewing.
  • Remember that the heat from the sun also presents a danger to your equipment, particularly to finder scopes and eyepieces with cemented elements. If you plan to observe by projection, set the focus well outside of where you would require it for direct viewing and then slowly refocus onto the projection surface. You may prefer to use older style eyepiece designs such as the Ramsden and Huygenian instead of modern multi-element designs because the former typically do not employ adhesives in their construction. Finally, place a cap(s) over your finder scope(s).
  • If you plan to observe the sun directly, place a full-aperture filter over the objective of your scope or, if you have reduced the normal aperture with a stop, place it over the effective aperture ("hole"). There are many materials currently on the market such as mylar, nickel-glass composites and special films intended for solar use that work well in this application. Do not use older devices such as a Herschel wedge.

Observing and recording guidelines

  • Make observations with an aperture range from 50mm to 80mm. If the aperture of your telescope is greater than 80mm, reduce it with an aperture stop. Note that a reduction in aperture can result in a productive gain in focal ratio with only small losses in resolution and brightness.
  • Scan the disk at several different powers. Use low power (40x-50x) and medium power (60x-70x) to see the entire disk and to identify the major groups and their structures. If seeing conditions permit, use high power (80x-90x) to aid in identifying tiny groups and achieving an accurate count.
  • Try to observe at the same time each day in order to maintain familiarity with the locations of groups.
  • Learn the Zurich and McIntosh classification systems so that you can use the evolutions of groups to achieve an accurate estimate.
  • Scan both limbs carefully. Often they contain spots that are hard to detect in cursory scans.
  • Be certain to count all of the groups and spots that you see.
  • Make several passes at counting groups and spots in order to take advantage of sudden improvements in seeing conditions.
  • Observe as frequently as you can in order to keep track of group evolutions and, thereby, improve the accuracy of your counts.
  • When you cannot observe for several days, use on resources the Internet to help keep track of evolutions (see attached list of addresses). DO NOT use these resources to "scale" your own observations. Most sources available via this medium use equipment and procedures that are different from the ones you use and can be expected to achieve different results.
  • When preparing a sunspot report for submission to the AAVSO, check to be sure that you have calculated the Wolf number (10g + f) correctly. NOTE: This tip does not apply to observers who use AAVSO's SunEntry software, which automatically checks arithmetic.
  • Submit your reports in a timely fashion. Remember that, to have your results included in the Solar Bulletin for a given month, your report must be received by the chairman of the Division by the 10th of the month following the month of observations. If you wish, you may submit your observations on a daily basis as you make the observations rather than sending them in one report at the end of the month.
  • (Notes on the central zone (cg and cs) counts from the SIDC website.) The central zone is defined as the circular area on the solar disk, with the same center as the solar disk, but with a radius that is half the solar radius. The "center of weight" position of the group determines if it is in the central zone. All spots belonging to a central zone group are counted, even if part of the group extends outside the limit circle. Conversely, none of the spots belonging to groups outside the central zone must be counted, even if some of them just fall within the limit. The central count for groups, spots and Wolf must always be less or equal to the corresponding total count. There is no relation between hemispheric counts and the central zone counts. The counting of the sunspots and the sunspot groups in the central zone is independent from the counting in the Northern and Southern hemisphere: a group or a sunspot appearing slightly North of the disk center will be counted once for the central zone and once for the Northern hemisphere. If sunspots or sunspot groups are close to the edge of the central zone, i.e. if they are at approximately half a solar radius away from the disk center, it can be difficult to determine if they are in or out of the central zone. In this case, the position of the sunspots or sunspot groups must be evaluated at 1200UT.

Further Reading

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