Looking through the telescope is one of the highlights of astronomy outreach activities. But given the pandemic, doing such activities are no longer considered a safe approach due to close contact of the observers with the eyepiece. MSA is among those affected by this given that our primary activity as an astronomy outreach community is our free telescope viewing setups. So just like most of the world the shift in astronomy outreach is through virtual means in observance of health and safety protocols.
Currently MSA is exploring non-contact alternatives to the viewing experience such as projection methods. There are many digital projection methods where an image can be electronically shown through a screen like your smartphone, laptop, or external monitor. However these entail access to additional gadgets and a power source.
An alternative option that we’ve worked on is a rear projection screen setup that can be used to show the Moon.
Unlike solar projection where it is easy to create a large projected image, the challenge for lunar projection is how much fainter the Moon is. The limitation of the Moon’s brightness limits the allowable projection size that can be made, so aperture considerations should also come into play in making the design. Larger aperture scopes have a greater light gathering power, so the bigger the aperture the better the projected image. This setup can also serve as a good way to illustrate that magnification is not always a good thing given that extended images are much dimmer when scaled up (inverse-square law).
The setup can be designed and modified easily with any material you have at home. What you need is a housing for the eyepiece lens and another to hold the screen in place. The screen to lens distance can be made adjustable to create a variation in projection size. The light path from the eyepiece to the screen must also be shielded from stray light for a clearer projection. Since I have an adapter for eyepiece projection I used it to test the different screen materials. Normal rear projection screen materials will not work given the relatively low degree of illumination from the Moon. If a material is too opaque then you wont be able to see a clear image, and if it is too transparent then most of the light will pass through creating a dim projection. Of the materials I tested the semi-clear plastic from the LBC parcel worked best (we are still exploring other materials to find out what gives the best view). I wrapped the material around the adapter and extended the tube to test for different projection sizes that work with the tested material. Once I found a suitable material I added a paper cup (with the insides painted black) to try extending the projection screen. A hole was made at the base of the cup to fit the t-threads on the adapter.
We are continuing to work on improving this (and even planning a 3D printed housing). We welcome everyone to tinker around and try creating a version of their own all in the spirit of bringing astronomy closer to the people while promoting safety. Do comment and share your results as well on our social media pages! Hoping this can be a helpful idea to those who continue to do astronomy outreach during these trying times.
Clear skies!
Norman Marigza
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