Solar Viewing

Click here for a live H-Alpha image of the Sun

The Sun today (click in image for full sized view)

 

  The images on the top row of this webpage are provided by NASA's SOHO spacecraft via NASA Goddard Space Flight Center. SOHO stands for Solar & Heliospheric Observatory .  The images on the bottom row are provided by the Stanford Solar Center, The National Solar Observatory and Mauna Loa Solar Observatory. (You can also see images of the Sun taken at the JAT Observatory by clicking on this solar gallery link.)

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 Most people use their telescopes to view planets, nebulas, galaxies or distant stars. But the brightest and closest star, our Sun is often over looked. Our Sun is what sustains life on earth and is responsible for the space weather that affects our planet. Viewing the can be fun and interesting, but care must be taken to ensure you protect your eyes and your equipment.  Warning look through any optical device pointed at the Sun without using an approved solar filter! Doing so can result in permanent eye damage!  Also be sure to cover your finder or guiding scope if you have one attached to your main telescope.  If you don't have the original cap use something dark that will not pass sunlight, and tape it securely. Failing to do so can result in your accessory scope being damaged.  People have also had their hair and skin burned by the focused sun light from uncovered guider or finder scopes.

There are many different types of solar filters.  Currently 3 types of solar filters are used at the JAT Observatory for imaging and observing the sun:

 The first filter used is an Inconel filter, commonly referred to as a white light filter.  The aluminum cell, glass mounted filter is coated with nickel-chromium stainless steel and blocks approximately 99% of the harmful energy from the sun. In addition it also allows natural color views of the sun. These types of filters are relatively inexpensive compared to some other types of solar filters and offer natural color views of the sun. The full aperture filter is just as it's name implies, it  fully covers the aperture (front) of the telescope.   Although the color is natural, very little if any surface detail can be seen with these types of filters. They are basically good for viewing sun spots and eclipses. This recent image showing the transit of Venus across the Sun was taken using a glass white light solar filter.  This filter (like all solar filters) should be  inspected before every use for cracks, scratches and pinholes in the coatings. Minor scratches on white light filters that let light through are easily repaired by using a black, fine point, felt tip, permanent marker to cover them up. The marker is used on the inside of the filter where the coatings are applied. Covering these minor scratches or pin holes in the coatings will prevent a phenomenon referred to as "ghosting" caused by the scattering of light through the pin hole, which causes multiple focal points. These multiple focal points are seen by your retina as ghost images.  Most of these types of filter can sustain up to 20 of these repairs per square inch without any loss of brightness or resolution.

To view the granularity of the surface or hot gas ejected from the surface into space (called prominence) you need a filter that blocks all light except the light at a wavelength of around 656nm. For this, a filter called a Hydrogen-Alpha filter, or H-alpha for short, is used. H-Alpha filters consists of 2 parts. Both parts are required in order to achieve the filtering process needed to view surface and prominence detail, as well as providing the protection from the harmful light and heat of the sun. The first part of the filter is called a "energy rejection filter" or ERF. The ERF blocks most of the harmful heat and light at the aperture. This allows only cool, red filtered light to reach narrow band pass filter that is connected to the eyepiece end of the scope. 

For prominence viewing The JAT Observatory will sometines use a Lumicon 1.5 angstrom H-alpha filter. The lumicon uses a 77mm ERF that is bonded to a step down mask that covers the front of the LX200GPS' aperture.  The step down mask is an aluminum plate that completely covers the aperture  of the telescope.  The ERF is bonded to the step down mask halfway between the center and the edge, in a hole that the 77mm ERF fits into.  The H-alpha filter is attached to the eyepiece end of the telescope and a standard eyepiece is inserted in the filter.  A small knob on the filter is used to tune the filter (within it's range) to a wavelength that allows the best visibility of the prominence.

For surface detail viewing, a Coronado MaxScope40 telescope) is used. The MaxScope40 is a complete, dedicated 40mm refractor scope with a Coronado MaxScope40 attached. The Solarmax40 uses a 40mm ERF attached to the front of the Maxscope and the H-Alpha filter attaches directly behind it. A tuning screw allows tuning of the H-Alpha filter around the 650 nm wavelength.   Using this tuning screw will also allow viewing the prominence as well as surface detail. The Maxscope40 assembly is piggybacked on top of the LX200GPS optical tube assembly. 

The downside of the H-Alpha filters is they are not cheap. It's not uncommon for a some H-alpha filters to approach $5000. But remember the old saying "you get what you pay for".  Another downside is it can be difficult to focus a camera that is sitting behind a Hydrogen-Alpha filter.  The positive side is Coronado has made the solar viewing affordable. Their Personal Solar Telescopes (PST) have set the new bench mark for solar scopes.  A user can have an entry level Hydrogen-Alpha or the Calcium K version of the PST for $500.

Here are some sources for information covering solar observing:
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The Solar Data Analysis Center at in Greenbelt, Maryland.
- Peter Meadows' website on solar observing in the UK.
- The Northern Virginia Astronomy Club Explains Hydrogen-Alpha filters and the basics of the Sun.
- Solar Observing FAQ Very detailed written by Jeff Medkeff.
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The Spectrohelioscope Network   An excellent page covering spectrohelioscopes.
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Images of the Sun taken by the Transition Region and Coronal Explorer (TRACE)

Go to the JATObservatory Home page

Updated 07/11/2015 - Please report broken links webmaster@jatobservatory.org