{"id":46604,"date":"2023-06-30T06:12:44","date_gmt":"2023-06-30T06:12:44","guid":{"rendered":"https:\/\/www.skyatnightmagazine.com\/?p=119933"},"modified":"2023-06-30T08:32:35","modified_gmt":"2023-06-30T08:32:35","slug":"take-advantage-of-recent-solar-activity-photograph-the-suns-dynamic-surface","status":"publish","type":"rss_feed","link":"https:\/\/c01.purpledshub.com\/bbcskyatnight\/rss_feed\/take-advantage-of-recent-solar-activity-photograph-the-suns-dynamic-surface\/","title":{"rendered":"Take advantage of recent solar activity \u2013 photograph the Sun\u2019s dynamic surface"},"content":{"rendered":"

Find out which solar filters are available to imagers, and what aspects of the solar surface each one reveals. <\/p>

By Pete Lawrence\n \t\t<\/p>

Published: Friday, 30 June 2023 at 12:00 am<\/p>

\n\n

Solar activity waxes and wanes over a period of around 11 years known as the solar cycle<\/a>. We are currently in Solar Cycle 25<\/a>, with solar scientists predicting an increase in activity over the next few years as we approach solar maximum.<\/span><\/p>\n

T<\/span>he Sun has been showing increased activity recently, making this is a great time to review some of the techniques required to image it, including the use of white light, hydrogen-alpha and calcium K filters to acquire different views of the solar disc.<\/p>\n

Solar imaging isn\u2019t without risk, and concentration needs to be high at all times to avoid accidents.<\/p>\n

Read our complete guide on how to safely photograph the Sun<\/a><\/strong><\/em><\/p>\n

\""The\"<\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/picture><\/div>
The same Sun photographed through three different filters (H-alpha, white-light and calcium-K) reveals markedly different views of our star. Credit: Pete Lawrence<\/span><\/figcaption><\/div>\n

It goes without saying that you should never look directly at the Sun nor point any instrument at it without using appropriate filters<\/a>.<\/p>\n

The two most common ways to observe the Sun using a telescope<\/a> are in white light or with a solar narrowband filter.<\/p>\n

Ready-made white-light filters are available or you can make your own (following instructions provided by the supplier).<\/p>\n

Narrowband filters are more expensive and can be either built into a dedicated solar telescope or supplied to convert a night-time telescope, typically a refractor, into a speciality narrowband instrument.<\/p>\n

Common narrowband filter types offer views in hydrogen-alpha or calcium-K, the former being the most common.<\/p>\n

Other wavelengths are also available.<\/p>\n

\""White\"<\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/picture><\/div>
White light view of the Sun. Credit: Pete Lawrence<\/span><\/figcaption><\/div>\n

What each solar filter shows<\/strong><\/h2>\n

Before you decide which filter to use when photographing the Sun, it pays to know the strengths of each.<\/p>\n

White-light filters<\/strong> show photospheric phenomena such as sunspots<\/a>, sunspot groups, faculae, limb darkening, solar granulation and \u2013 very rarely \u2013 solar flares.<\/p>\n

Features in white light tend to change in form subtly over the course of a few hours or days.<\/p>\n

H-alpha filters<\/strong> reveal chromospheric and inner atmosphere (corona) features including active regions, plage, spots, spicules, filaments, fibrils, dark mottles, solar prominences<\/a> and flares.<\/span><\/p>\n

Calcium-K<\/strong> filters give views similar to white light, enhanced with elements of the solar chromosphere. This can include bright prominences.<\/p>\n

Active sunspot regions are particularly clear with a calcium-K filter, as are the bright plage regions associated with them.<\/p>\n

H-alpha views are the most dynamic and can change noticeably over the course of hours and sometimes minutes.<\/p>\n

Calcium-K features exhibit changes over timescales similar to the white-light view.<\/p>\n

\""Active\"<\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/picture><\/div>
Active Region 2209 Imaged in Calcium K by Mike Garbett, Walsall, W. Midlands, UK. Equipment: HEQ5 Pro, Lunt 60, Lunt CaK1200, x2 Barlow, PG Grasshopper camera.<\/span><\/figcaption><\/div>\n

Getting a clear shot<\/strong><\/h2>\n

Whichever filter you use, the goal is to reduce the intensity of the Sun to a level suitable for direct imaging.<\/p>\n

Once that\u2019s done, the approach is then no different to that required for, say, the Moon.<\/p>\n

Here, monochrome high-frame-rate cameras are king, their rapid capture rates helping to overcome seeing<\/a> effects.<\/p>\n

In addition, the essentially monochromatic nature of narrowband filters removes the effects of atmospheric dispersion where lower altitudes spread an object\u2019s light into a spectrum of colour, effectively muddling the view.<\/p>\n

\""The\"<\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/picture><\/div>
The afternoon Sun, by Rob Lyons, Vancouver, Canada, 14 January 2023. Equipment: ZWO ASI 533MM Pro camera, Daystar Solar Scout SS60-DS H-alpha solar telescope, Sky-Watcher Solar Quest mount<\/span><\/figcaption><\/div>\n

Similar refinement can be achieved in white light by using a green filter, which increases the contrast of the slightly magenta dividing lines between solar granules, the fine rice-paper-like pattern that crosses the photosphere.<\/p>\n

Near solar maximum, sunspots litter the Sun\u2019s disc on a daily basis.<\/p>\n

The next solar maximum is predicted for July 2025 (plus or minus eight months), making this a great time to begin your visual record of our nearest star.<\/p>\n

\""The\"<\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/picture><\/div>
The solar disk, by Alex Dean, Nottingham, 27 May 2022. Equipment: ZWO ASI178MM camera, Lunt LS50THa B400PT H-alpha solar scope, Fornax LighTrack II mount<\/span><\/figcaption><\/div>\n

Equipment<\/strong><\/h2>\n