Though practically you can grind and polish your mirror at any time during the year. However in my experience, if you do the mirror making in few select seasons of India, chances of success will be very high.
So let me tell you about those seasons and why I think they are the best when you plan making your own mirror.
Season 1 – Monsoon
In India, monsoon or rainy season starts at the start of the June month by first hitting the Kerla and then reaching to Mumbai by the second week of June and then slowly spreading itself to entire India within a month. In India we all enjoy rainy season. It provide us relief from the scorching heat we go through between March to June. Monsoon is also something eagerly awaited by our farmers for their crops.
Why monsoon is the best season to make the mirrors?
Because rains settle down all the dust around us!
You know how dreadful dust particles are during fine grinding of the mirror. A small unnoticed particle can scratch the glass surface and you have to go back to rough grinding to remove that scratch. A dust particle is more dreadful during the polishing stage because you have to go back several steps to regrind your mirror. We not only lose time but also lose our interest to make the mirror.
I usually do my mirror making between June to September. I hold my work in October unless required because weather becomes dusty again due to high winds and occasional rains with thunderstorms.
I continue mirror making from November month and will let you know the reason for the the same in next section.
Season 2 – Winter
November is the onset of winter in India which continues till the end of February. In most of the southern and coastal regions, temperature becomes more pleasant and hover between 15-27 degree Celsius. In northern India however it goes below to 5-10 degrees Celsius. Some people enjoy it and some just can’t bear it.
If you miss the monsoon somehow, the next best season to make the telescope is winter!
Why?
Because in India, winter is a less dusty season due to the formation of dew every night which helps keep settling the dust everyday.
In some countries, winter become more dusty because of excessive heating used in Homes. In India, we don’t usually have that luxury and home temperatures are not much different than outside temperature.
There is another reason probably every astronomer in India loves winter because we get the best clear view of the night sky.
Now between March to May, I usually never work on the mirrors due to summer season in India and because of the fear of scratches. In India, summer is a very dusty season.
If you live in a different country, this information may equally be applicable but in different time or months of the year.
Now I told you about the best seasons to make the mirror. Hope this knowledge though may not look very critical will help you to make your mirror successfully.
Thank you!
Astro Khan Telescope Making 