What you choose to celebrate, and how, is up to you and your family and friends.
Here are some notable internationally recognized days, birthdays relevant to pantheism, and other significant or fun events.

January

16: Martin Luther King Day: Anti-discrimination

February

2: Imbolc
12: Darwin’s birthday: Evolution
14: Valentine’s Day: Day of partners
15: Birthday of Galileo: Solar system
17: Martyrdom of Giordano Bruno: Religious freedom

March

1:  Yellowstone Park established: focus on parks
3: World Wildlife Day
8: International Women’s Day
14: Einstein’s birthday: the Universe
21/22: Spring equinox
23: World Meteorological Day: Climate & weather

April

1: Fools’ Day – fun and jokes
7: World Health Day: Focus on healthy living
21: John Muir’s birthday — nature reserves 
22: Earth Day
22-28: International Dark sky week

May

1:   Mayday/Beltane: Fire
        International Workers’ Day
15: International Day of Families 
Variable: Mothers’ Day

June

5:   World Environment Day
8:   World Oceans Day
20: World Refugee Day

21/22: Midsummer solstice
Variable: Fathers’ Day

July

4: USA: Independence Day 
5: Anniversary of supernova that created Crab Nebula
11: World Population Day 

12: Simplicity Day (Birthday of Thoreau) 
14: France: Bastille Day – liberty, equality, fraternity
20: Moon landing day (1969)

August

6:   Hiroshima Day – anti-nuclear weapons 
9:   International Indigenous Peoples Day 
12: Perseid meteor shower: Starwatching
26: Krakatoa day: global tectonics.
Harvest (according to location)

September

8:   International Literacy Day
15: International Democracy Day
21: International Peace Day
21/22: Autumn equinox

October

2: International Day of Non-Violence (Gandhi’s birthday)
4: World Animal Day
16: World Food Day
31: Halloween/Samhain

November

2: All Soul’s Day – remembrance of the dead
13: World Kindness Day
16: International Day for Tolerance
23: International Buy Nothing Day
24: Spinoza’s birthday
30: John Toland’s birthday (creator of word pantheist)

December

1: World AIDS day
2: International Day for the Abolition of Slavery
10: Geminids: Starwatching  
10: Human Rights Day

21: Winter solstice
22: International Arbor Day – tree planting
25: Newton’s Birthday

There is no reason why we should not celebrate the key feasts of our own traditional cultures, giving them in each case our own special meaning.
In the Christian case Christmas and Easter were purloined from pagan religions, therefore we are repossessing them for their original meanings.

A Pantheist and Pagan Almanac, 2013-2016
Scientific pantheism – main page.