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Dr Simon Bennett FRAS

Get Ready for the Mercury Transit!

Warning: NEVER look at the Sun without the use of proper safety equipment. This can cause permanent damage to the eyes.  We will talk about some of the available equipment below, but if you have any concerns at all, please give us a call.

With the next transit of Mercury coming up on Monday 11th November, you may be thinking about wanting to have a look. Of course, looking directly at the Sun is dangerous, especially through an unfiltered telescope. However, with the right equipment, you can easily and safely observe the Sun and any transit!

There are 2 types of solar viewing: White light, and H-Alpha (Ha).

White light

White light filters work by reducing the intensity of the light passing through by 99.999%. This not only makes the Sun safe to look at, but you can also place it in front of an optical device (including telescopes and binoculars) to view the sun at a higher magnification. In white light, you see the "surface" of the Sun, as well as Sunspots, any granulation on the surface, as well as transits. Transits don't just have to be planets, they can also be satellites (such as the ISS), birds, planes, and also the Moon when eclipses occur!

White light filters are typically very inexpensive and easy to use. They can simply be mounted in front of any optical device you are using (note: It is important that the filter goes at the front of the optical train. If the filter goes at the back, such as between an eyepiece and your eye, irreversible damage could occur to your vision). They were most popular in the form of glass filters that sat over the front of a telescope, however more popular recent options come in the form of a metallic sheet, similar in appearance to aluminium foil. These are less fragile to use than glass covers, and are more versatile in that they can be made larger at cheaper prices.

Explore Scientific manufacture the Solarix solar film. If you are looking for a great-value all-in-one solution to see the transit, there is the Solarix telescope, complete with the needed safety equipment. The film is available in A4 sheets here.

Baader Planetarium manufacture the AstroSolar Safety materials. This can be bought in either A4 sheets if you would like to make your own holder, or can be bought with pre-built holders for telescopes, spotting scopes and binoculars. If you would like to know which size pre-built you need, please click here. Baader's sheets come in 2 options: ND5.0 for visual use, or ND3.8 for photographic use. Do not use the ND3.8 for visual use, as it has been designed to give brighter images of the Sun for shorter photographic exposures, too bright for visual use. Photographs can easily be taken through the ND5.0 as well.

You can also get Solar Wedges (Herschel Prisms) built by Baader Planetarium, Lunt Engineering, and Altair Astro. These are designed to work with refractors without rear elements, and provides a sharper view of the Sun in white light. The Baader and Altair ones even come with a solar finder built-in to the back, making it easy to find the otherwise surprisingly difficult to find Sun!

Hydrogen Alpha (Ha)

H-Alpha filters work by passing through a single specific wavelength of light, the 656.3nm Ha wavelength. Powerful eruptions, known as prominences (Solar flares), rise up from the edge of the Sun and fall back dawn on the surface. Also the surface itself is generous with exciting effects, like turbulences, flares, and filaments. Unbelievable enormous quantities of vibrant energy, directly before your eyes.

Ha filtering comes in 2 forms: Dedicated solar telescopes, and seperate Ha filters. The most popular dedicated solar telescopes are the Lunt Single Stack and Double Stack telescopes, and the Daystar Solar Scout telescopes. The Lunts are more expensive, but do not require power, and are ready to view immediately without having a "warm-up" time.

Daystar also offer their famous "Quark". This product is used like a powered Barlow lens, in that it sits behind the diagonal and in front of an eyepiece. This allows you to convert any* refractor into a Ha telescope!

*Up to 80mm, you would only need the Quark itself. Between 80mm and 100mm, you would need a UV/IR cut filter, such as the Baader or Astronomik ones, in front of the diagonal. Above 100mm, you would need a front-mounted Energy Rejection Filter (ERF) to block off the UV/IR rays from entering the telescope altogther.

In summary, solar viewing can be a very safe and enjoyable experience for everyone. The surface of the Sun is constantly changing, with dynamics such as solar flares erupting and falling back down within hours, sunspots evolving over the rotating surface, and filaments opening up before your eyes.

If you have any questions at all, please do not hesitate to speak to Joseph or Simon, by calling 01353 776 199, or e-mailing sales@widescreen-centre.co.uk.