May is a month of spring in the Northern Hemisphere and autumn in the Southern Hemisphere. Therefore, May in the Southern Hemisphere is the seasonal equivalent of November in the Northern Hemisphere and vice versa. Late May typically marks the start of the summer vacation season in the United States (Memorial Day) and Canada (Victoria Day) that ends on Labor Day, the first Monday of September.
May (in Latin, Maius) was named for the Greek goddess Maia, who was identified with the Roman era goddess of fertility, Bona Dea, whose festival was held in May. Conversely, the Roman poet Ovid provides a second etymology, in which he says that the month of May is named for the maiores, Latin for "elders," and that the following month (June) is named for the iuniores, or "young people" (Fasti VI.88).
Mayovka, in the context of the late Russian Empire, was a picnic in the countryside or in a park in the early days of May, hence the name. Eventually, "mayovka" (specifically, "proletarian mayovka") came to mean an illegal celebration of May 1 by revolutionary public, typically presented as an innocent picnic.
Eta Aquariids meteor shower appears in May. It is visible from about April 21 to about May 20 each year with peak activity on or around May 6. The Arietids shower from May 22 – July 2, and peaks on June 7. The Virginids also shower at various dates in May.
Ancient Roman observances
Under the calendar of ancient Rome, the festival of Bona Dea fell on May 1, Argei fell on May 14 or May 15, Agonalia fell on May 21, and Ambarvalia on May 29. Floralia was held April 27 during the Republican era, or April 28 on the Julian calendar, and lasted until May 3. Lemuria (festival) fell on 9,11, and 13 May under the Julian calendar. The College of Aesculapius and Hygia celebrated two festivals of Rosalia (festival), one on May 11 and one on May 22. Rosalia was also celebrated at Pergamon on May 24–26. A military Rosalia festival, Rosaliae signorum, also occurred on May 31. Ludi Fabarici was celebrated on May 29 – June 1. Mercury would receive a sacrifice on the Ides of May (May 15). Tubilustrium took place on May 23 as well as in March. These dates do not correspond to the modern Gregorian calendar.
- emerald which is emblematic of love and success.
- The May birth flowers are the Lily of the Valley and the Crataegus monogyna. Both are native throughout the cool temperate Northern Hemisphere in Asia, Europe, and in the southern Appalachian Mountains in the United States, but have been naturalized throughout the temperate climatic world.
- Epigaea repens is a North American harbinger of May, and the floral emblem of both Nova Scotia and Massachusetts. Its native range extends from Newfoundland south to Florida, west to Kentucky in the southern range, and to Northwest Territories in the north.
- Working class history month
- Better Hearing and Speech Month
- In Catholic tradition, May is the Month of the Blessed Virgin Mary. See May devotions to the Blessed Virgin Mary
- Celiac Awareness Month
- Cystic Fibrosis Awareness Month.
- Ehlers-Danlos Syndrome Awareness month
- Flores de Mayo (Philippines)
- Garden for Wildlife month
- Huntington's Disease Awareness Month (International)
- International Mediterranean Diet Month
- Kaamatan harvest festival (Labuan, Sabah)
- New Zealand Music Month (New Zealand)
- National Pet Month (United Kingdom)
- National Smile Month (United Kingdom)
- Season of Emancipation (April 14 to August 23) (Barbados)
- Skin Cancer Awareness Month
- South Asian Heritage Month (International)
- World Trade Month
- Asian Pacific American Heritage Month
- National ALS Awareness Month
- Bicycle Month
- National Brain Tumor Awareness Month 
- National Burger Month 
- Community Action Awareness Month (North Dakota)
- National Electrical Safety Month
- National Foster Care Month
- National Golf Month 
- Jewish American Heritage Month
- Haitian Heritage Month
- Hepatitis Awareness Month
- Mental Health Awareness Month
- National Military Appreciation Month
- National Moving Month 
- National Osteoporosis Month 
- National Stroke Awareness Month
- National Water Safety Month 
- Older Americans Month 
Non-Gregorian observances, 2020
(All Baha'i, Islamic, and Jewish observances begin at the sundown prior to the date listed, and end at sundown of the date in question unless otherwise noted.)
- List of observances set by the Bahá'í calendar
- List of observances set by the Chinese calendar
- List of observances set by the Hebrew calendar
- List of observances set by the Islamic calendar
- List of observances set by the Solar Hijri calendar
Movable observances, 2020
- Phi Ta Khon (Dan Sai, Loei province, Isan, Thailand) Dates are selected by village mediums and can take place anywhere between March and July.
- National Small Business Week (United States): May 5 – 11
- National Hurricane Preparedness Week (United States): May 5 – 11
- New Zealand Sign Language Week: May 6 – 12
- Green Office Week (Britain, United States): May 13 – 17
- Walk Safely to School Day (Australia): May 17
- Emergency Medical Services Week (United States): May 19 – 25
- Bike to Work Week Victoria (May 27 – June 2)
Movable Western Christian observances, 2020 dates
Sunday after Divine Mercy Sunday: May 5
Monday and Tuesday in the week following the third Sunday of Easter: May 6–7
Fourth Sunday after Easter: May 12
Fourth Friday after Easter: May 17
Third Sunday of May: May 19
Sunday preceding the Rogation days: May 26
Monday, Tuesday, and Wednesday preceding Feast of the Ascension: May 27–29
- Minor Rogation days
39 days after Easter: May 30
- Feast of the Ascension
Movable Eastern Christian observances, 2020 dates
Wednesday after Pascha: May 1
Thursday after Pascha: May 2
Friday after Pascha: May 3
Saturday after Pascha: May 4
8th day after Pascha: May 5
2nd Tuesday of Pascha, or 2nd Monday of Pascha, depending on region: May 6 or May 7
2nd Sunday following Pascha: May 12
4th Sunday of Pascha: May 26
Wednesday after the Sunday of the Paralytic: May 29
Last Friday in April to the first Sunday in May: April 26 – May 5
First Thursday: May 2
- Arbour Day (Nova Scotia, Canada)
- National Day of Prayer (United States)
- National Day of Reason (United States)
First Saturday: May 4
- Kentucky Derby (moved to September 5, 2020)
- Free Comic Book Day
- Green Up Day (Vermont, United States)
- World Naked Gardening Day
First Sunday: May 5
- Mother's Day (Angola, Cape Verde, Hungary, Lithuania, Mozambique, Portugal, Spain)
- World Laughter Day
First full week: May 5–11
- National Teacher Appreciation Week (United States)
- North American Occupational Safety and Health Week
Tuesday of First full week: May 4
Wednesday of first full week: May 8
Second week in May: May 5–11
First Tuesday: May 7
Friday preceding Second Sunday in May: May 10
Saturday closest to May 10: May 11
Second Saturday: May 8
- International Migratory Bird Day (Canada, the United States, Mexico, Central and South America, and the Caribbean)
- National Tree Planting Day (Mongolia)
Second Weekend: May 11–12
Second Sunday: May 9
- National Nursing Home Week (United States)
- Children's Day (Spain)
- Father's Day (Romania)
- Mother's Day (Anguilla, Aruba, Australia, Austria, Bahamas, Barbados, Bangladesh, Belgium, Belize, Bermuda, Bonaire, Brazil, Brunei, Canada, Chile, Colombia, Cuba, Croatia, Curaçao, Czech Republic, Denmark, Ecuador, Estonia, Finland, Germany, Greece, Grenada, Honduras, Hong Kong, Iceland, India, Italy, Jamaica, Japan, Latvia, Malta, Malaysia, the Netherlands, New Zealand, Pakistan, Peru, Philippines, Puerto Rico, Singapore, Slovakia, South Africa, Suriname, Switzerland, Taiwan, Trinidad and Tobago, Turkey, United States, Uruguay, Venezuela, Zimbabwe)
- State Flag and State Emblem Day (Belarus)
- World Fair Trade Day
- National Nursing Week (United States)
Third Weekend, including Friday: May 14-16
Third Friday: May 21
- Arbour Day (Prince Edward Island, Canada)
- National Defense Transportation Day
- Endangered Species Day (United States)
- National Pizza Party Day (United States)
Third Saturday: May 15
- The Preakness Stakes is run, second jewel in the triple crown of horse racing.
- Armed Forces Day (United States)
- Culture Freedom Day
- Sanja Matsuri
- World Whisky Day
Third Sunday: May 16
- Commemoration Day of Fallen Soldiers
- Father's Day (Tonga)
- Feast of Our Lady of the Audience
- Sanja Matsuri (Tokyo, Japan)
Monday on or before May 24: May 24
Third Monday: May 17
Monday on or before May 25: May 24
Last Monday preceding May 25: May 24
May 24, or the nearest weekday if May 24 falls on a weekend: May 24
- Bermuda Day (Bermuda)
Saturday closest to May 30: May 29
- Armed Forces Day (Spain)
Last Weekend: May 29–30
Last Sunday: May 30
- Arbor Day (Venezuela)
- Children's Day (Hungary)
- Mother's Day (Algeria, Dominican Republic, Haiti, Mauritius, Morocco, Sweden, Tunisia)
- Turkmen Carpet Day (Turkmenistan)
Last Monday: May 31
- Heroes' Day (Turks and Caicos Islands)
- Memorial Day (United States), a public holiday, is on May 30, but observed on the last Monday in May.
- Ratu Sir Lala Sukuna Day (Fiji), removed as a national holiday in 2010.
Last Wednesday: May 26
Last Thursday: May 27
- Take a Girl Child to Work Day (South Africa)
Fixed observances in May
- April 29 to May 5 in Japan, which includes four different holidays, is called "Golden Week". Many workers have up to 10 days off. There is also 'May sickness', where new students or workers start to be tired of their new routine. (In Japan the school year and fiscal year start on April 1.)
- May 1
- May 2
- May 3
- May 4
- Anti-Bullying Day (United Nations)
- Bird Day (United States)
- Cassinga Day (Namibia)
- Death of Milan Rastislav Štefánik Day (Slovakia)
- Greenery Day (Japan)
- International Firefighters' Day
- May Fourth Movement commemorations:
- Remembrance Day for Martyrs and Disabled (Afghanistan)
- Remembrance of the Dead (Netherlands)
- Restoration of Independence day (Latvia)
- Star Wars Day (International observance)
- World Give Day
- Youth Day (Fiji)
- May 5
- Children's Day (Japan, Korea)
- Cinco de Mayo
- Constitution Day (Kyrgyzstan)
- Coronation Day (Thailand)
- Europe Day in Europe (uncommon usage, largely replaced by May 9).
- Feast of al-Khadr or Saint George (Palestinian people)
- Indian Arrival Day (Guyana)
- International Midwives' Day
- Liberation Day (Denmark)
- Liberation Day (Netherlands)
- Lusophone Culture Day (Community of Portuguese Language Countries)
- Martyrs' Day (Albania)
- Patriots' Victory Day (Ethiopia)
- Senior Citizens Day (Palau)
- Tango no sekku (Japan)
- May 6
- Martyrs' Day (Gabon)
- Martyrs' Day (Lebanon and Syria)
- International No Diet Day
- Teachers' Day (Jamaica)
- The first day of Hıdırellez (Turkey)
- St George's Day related observances (Eastern Orthodox Church):
- May 7
- May 8
- Miguel Hidalgo's birthday (Mexico)
- Parents' Day (South Korea)
- Time of Remembrance and Reconciliation for Those Who Lost Their Lives during the Second World War, continues to May 9
- Truman Day (Missouri, United States)
- White Lotus Day (Theosophy)
- World Red Cross and Red Crescent Day
- Veterans Day (Norway)
- VE Day in Western Europe. In Eastern Europe it is celebrated on May 9.
- May 9
- Anniversary of Dianetics (Church of Scientology)
- Europe Day (European Union)
- Liberation Day (Guernsey), commemorating the end of the German occupation of the Channel Islands during World War II.
- Liberation Day (Jersey), commemorating the end of the German occupation of the Channel Islands during World War II.
- Time of Remembrance and Reconciliation for Those Who Lost Their Lives during the Second World War, continued from May 8.
- Victory Day observances, celebration of the Soviet Union victory over Nazi Germany (Soviet Union, Azerbaijan, Belarus, Bosnia and Herzegovina, Georgia, Israel, Kazakhstan, Kyrgyzstan, Moldova, Russia, Serbia, Tajikistan, Turkmenistan, Uzbekistan)
- Victory Day over Nazism in World War II (Ukraine)
- Victory and Peace Day (Armenia) marks both the capture of Shusha (1992) in the First Nagorno-Karabakh War, and the end of World War II.
- May 10
- Children's Day (Maldives)
- Confederate Memorial Day (North Carolina and South Carolina)
- Constitution Day (Federated States of Micronesia)
- Golden Spike Day (1869 – Completion of the First Transcontinental Railroad – Promontory Summit, Utah)
- Independence Day (Romania), celebrating the declaration of independence of Romania from the Ottoman Empire in 1877.
- Liberation Day (Sark), commemorating the end of the German occupation of the Channel Islands during World War II.
- May 11
- May 12
- May 13
- May 14
- May 15
- Beginning of Tourette Syndrome awareness month. It ends on June 15
- Army Day (Slovenia)
- Constituent Assembly Day (Lithuania)
- Independence Day (Paraguay)
- International Day of Families
- Nakba Day (Palestinian communities)
- Peace Officers Memorial Day (United States)
- Republic Day (Lithuania)
- Saint Ubaldo Day
- Teachers' Day (Colombia, Mexico, South Korea)
- May 16
- May 17
- National Day Against Homophobia (Canada)
- International Day Against Homophobia, Transphobia and Biphobia, also known as IDAHOT
- Birthday of the Raja (Perlis)
- Children's Day (Norway)
- Constitution Day (Nauru)
- Galician Literature Day (Galicia (Spain))
- World Hypertension Day
- World Information Society Day
- Liberation Day (Democratic Republic of the Congo)
- Navy Day (Argentina)
- Norwegian Constitution Day
- May 18
- Baltic Fleet Day (Russia)
- Battle of Las Piedras Day (Uruguay)
- Day of Remembrance of Crimean Tatar genocide (Ukraine)
- Flag and Universities Day (Haiti)
- Independence Day (Somaliland) (unrecognized)
- International Museum Day
- Mullivaikkal Remembrance Day (Sri Lankan Tamils)
- Revival, Unity, and Poetry of Magtymguly Day (Turkmenistan)
- Teacher's Day (Syria)
- Victory Day (Sri Lanka)
- World AIDS Vaccine Day
- May 19
- May 20
- May 21
- Afro-Colombian Day (Colombia)
- Circassian Day of Mourning (Circassians)
- Day of Patriots and Military (Hungary)
- Navy Day (Chile)
- Saint Helena Day, celebrates the discovery of Saint Helena in 1502.
- World Day for Cultural Diversity for Dialogue and Development (International)
- One of the three festivals of Vejovis (Roman Empire)
- May 22
- Abolition Day (Martinique)
- Harvey Milk Day (California)
- International Day for Biological Diversity (International)
- National Maritime Day (United States)
- National Sovereignty Day (Haiti)
- Republic Day (Sri Lanka)
- Translation of the Relics of Saint Nicholas from Myra to Bari (Ukraine)
- Unity Day (Yemen)
- World Goth Day
- May 23
- May 24
- Feast of Mary Help of Christians (Roman Catholicism)
- Aldersgate Day/Wesley Day (Methodism)
- Battle of Pichincha Day (Ecuador)
- Commonwealth Day (Belize)
- Independence Day (Eritrea)
- Lubiri Memorial Day (Buganda)
- Saints Cyril and Methodius Day (Eastern Orthodox Church) and its related observance:
- Bulgarian Education and Culture and Slavonic Literature Day (Bulgaria)
- Saints Cyril and Methodius, Slavonic Enlighteners' Day (North Macedonia)
- May 25
- Africa Day (African Union)
- African Liberation Day (African Union)
- Day of Youth
- Geek Pride Day
- Independence Day (Jordan)
- Liberation Day (Lebanon)
- May Revolution (or Revolución de Mayo), a national holiday in Argentina
- International Missing Children's Day
- Last bell (Russia, post-Soviet countries)
- Liberation Day (Lebanon)
- National Day (Argentina)
- National Missing Children's Day (United States)
- National Tap Dance Day (United States)
- Towel Day
- May 26
- May 27
- May 28
- May 29
- May 30
- May 31
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- The Earth passed the junction of the signs at 13:49 UT/GMT May 20, 2020, and will pass it again at 19:37 UT/GMT May 20, 2021.
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- "Raising awareness of Huntington's Disease".
- "International Mediterranean Diet Month". oldwayspt.org.
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- "May is Hepatitis Awareness Month". cdc.gov. 2 April 2021.
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- "National Osteoporosis Foundation". nof.org.
- "Stroke Awareness Resource Center". Stroke.org.
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