On November 11th, the planet Mercury will move across the face of our Sun. This celestial event with start around lunchtime – around 12:35h GMT. The time of greatest transit, that is when Mercury “is near the middle of Sun” is around 15:19hGMT, and the transit event ends around 18:04h GMT, however for the UK the Sun sets around 16:15h GMT so we won’t be able to see the end of this event. You can read more about this event here.
Celestron offers two sizes of Solar filters that can be used to view and image Mercury’s transit. These filters are called EclipSmart Solar Filters. Although these filters were produced for the 2017 Great American Total Solar Eclipse, they can of course be used for day-to-day Solar observing and imaging and, of course, for this transit event.
The solar filters are designed specifically for use with the following telescopes:
The filter material used in the EclipSmart filters use Celestron’s ISO compliant Solar Safe filter technology to provide protection from harmful UV/IR solar radiation and to block 99.999% of visible light. You can read more about Solar Safe technology here. In use, the filter gives a yellow “normal-looking” Sun colour, that is pleasing to the eye.
The filter film holders are actually made from the telescope’s dust cap; basically, and to put it simply, it is a telescope dust cover with a solar filter in the middle of it. From an aesthetic point of view, this design which makes use of telescope’s (modified) dust cap is very nice, as it transforms the telescope to look like a dedicated, purpose made professional looking solar instrument. Furthermore, the use of the plastic dustcap means that the filter units are not too heavy, with the 8″ model weighing in at only 121g meaning a telescopes balance will not be affected when the filter is fitted.
Attaching (and removing) the Solar filter to a telescope is the same process as for the “standard” dust cap supplied with the telescope. Protruding tabs around the inside of the filter holder will require you to give it a firm “push and then twist” action to lock the filter in position for secure attachment. For added safety, for keeping the filter in place, Celestron supply two safety Velcro straps and four self-adhesive Velcro pads (on opposite sides of the telescope: one pad attached to the telescope tube and the other pad on the filter holder with the strap attached to both pads) – see the image at the bottom to see how they are fitted.
Once the filter is attached you can then safely view or image the Sun. However if your telescope has an optical magnified viewfinder (e.g. 9×50) please remember to leave their dust caps on (i.e. no light to enter the viewfinder) otherwise you may be accidentally blinded and/or cause damage to the finder.
Finally, although these filters use a modified telescope dust cover, they are not intended for permanent use as a dust cover. Please take it off, store it safely and replace with the original “proper” dust cover after you have ended your Solar session (remembering to point your telescope AWAY from the Sun before removing the Solar filter!!).