September 20 1970 was a Sunday.
August 20, 1981, was a Thursday.
20 September 1980 was a Saturday.
Friday
Actually 20th or 21st June is Winter Solstice, the official start of winter is 1st June. The last day of Winter is 31st August.
Usually March 21st, but sometimes the vernal equinox can fall on March 20th, such as in 2012.
It has not changed. The March equinox can be on the 19th, 20th or 21st of March. It is not at the exact same moment every year, so it does vary. It was on the 20th of March in 2016, when the question was asked. In other years it can be different.
The first day of spring is never on March first. It usually falls on March 20, 21, 22, or 23. In the years 2010 through 2017 it will fall on the 20th of March. In the Southern Hemisphere, of course, it will be the first day of autumn.
20th August fell on a Thursday in 1959.
It was a Sunday.
August 20th, 1981 was a Thursday.
The 1st of August 1981 was a Saturday.
Saturday.
It was a Friday.
August 20th, 1996 fell on a Tuesday.
It was a Friday.
Sunday
It was a Friday.
20th August 1934 was a Monday.
20th of August 1965 was a Friday.