May is a month of autumn in the Southern Hemisphere and spring in the Northern Hemisphere (Summer in Europe). Therefore May in the Southern Hemisphere is the seasonal equivalent of November in the Northern Hemisphere and vice versa. No other month begins or ends on the same day of the week as May in any year. This month is the only month to have these two properties. However, May like all other months does share starting and ending days with various months of both previous and following years: every year, May starts and ends on the same day of the week as January of the following year.
Additionally, in years immediately before common years, May starts and ends on the same day of the week as October of the following year; it also ends on the same day of the week as February of the following year. In years immediately before leap years, May starts on the same day of the week as April of the following year; it also both starts and ends on the same day of the week as July of the following year.
In a common year, May both starts and ends on the same day of the week as August of the previous year; it also ends on the same day of the week as November of the previous year. In a leap year, May both starts and ends on the same day of the week as March of the previous year; it also starts on the same day of the week as November and ends on the same day of the week as June, both of the previous year. In a leap and a year immediately after that, May starts on the same day of the week as February of the previous year.
Late May typically marks the start of the summer vacation season in the U.S.
History and origin
The month May 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).
Events 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.)
- In the neopagan Wheel of the Year, May begins on Beltane in the northern hemisphere and Samhain in the southern hemisphere.
- May 1 is Lei Day in Hawai`i. The custom is to wear a lei throughout the day.
- May 1 is the feast of St. Joseph the worker in the Roman Catholic calendar. In the Catholic Church the month of May is dedicated to and honors the Blessed Virgin Mary.
- May 1 in the Irish calendar is Beltane (Bealtaine), the first day of Summer, and a public holiday is held on the first Monday in May.
- May 1 is May Day in many countries. This is also celebrated as Labour Day in many countries.
- May 1 is May Day in the United Kingdom, however the public holiday is held on the first Monday in May.
- The night before May 1 in Germany it is an old custom to plant a "Maypole" to honor someone. Often young men set up an adorned birch in front of their girlfriend's house.
- May 3 is when the Polish Constitution Day is celebrated in Poland.
- May 3 is Constitution Day in Japan.
- The first Saturday in May is the date of the annual Kentucky Derby, the most famous horse race in the United States.
- May 4 is the day of Remembrance of the Dead in the Netherlands, commemorating all the casualties in military conflicts involving the Netherlands.
- May 4 is Liberation Day in Denmark, celebrating the ending of the German occupation from April 9, 1940, to May 4, 1945.
- May 4 is considered by many Star Wars fans to be Star Wars Day for the pun "May the fourth be with you", which sounds similar to "May the force be with you".
- May 5 is when Cinco de Mayo or the Batalla de Puebla is celebrated in Mexico. It is also celebrated widely in the United States.
- May 5 is the Children's Day in Japan and Korea
- May 5 is Liberation Day in the Netherlands, celebrating the ending of the German occupation.
- May 5 is Europe Day in Europe (uncommon usage, largely replaced by May 9).
- May 8 is VE Day in Western Europe. In Eastern Europe it is celebrated on May 9.
- May 9 is Europe Day in the European Union.
- May 9 is Victory Day in the former Soviet Union, celebrating the capitulation of Nazi Germany.
- May 10 is Golden Spike Day (1869 – Completion of the First Transcontinental Railroad – Promontory Summit, Utah)
- May 10 is Mother's Day in Mexico, Guatemala, and El Salvador.
- May 12 is International Nurses Day.
- May 12 is the day of the Finnish language in Finland.
- May 12 is International Awareness Day for Chronic Immunological and Neurological Diseases (CIND). These diseases include Neurofibromatosis, Chronic Fatigue Immune Dysfunction Syndrome (CFIDS)/Myalgic Encephalomyelitis, Fibromyalgia, Gulf War Syndrome and Multiple Chemical Sensitivity.
- May 13 is when the Catholic Church honors the first apparition of Our Lady of Fatima to the three children of Fátima, Portugal – May 13, 1917.
- May 13 was Lemuria the day for seeing spirits to the other side in ancient Rome, the holiday was later moved to November 1st and called All Souls' Day.
- May 15 is the beginning of Tourette Syndrome awareness month. It ends on June 15th.
- May 17 is Norwegian Constitution Day.
- May 17 is Vesak full moon poya day (Buddhism's Holiest Day), The day of birth, enlightenment (nirvāna), and passing away (Parinirvāna) of Gautama Buddha.
- May 18 is International Day of Capitalism
- May 21 is when the Battle of Iquique (Combate Naval de Iquique) is celebrated in Chile, and it is a national holiday.
- May 24 is when Eritrea celebrates its Independence Day (Independence from Ethiopia).
- May 24 is remembered and celebrated in Ecuador as the day of the Battle of Pichincha – May 24, 1823.
- May 25 is the Liberation Day of Lebanon after the withdrawal of Israeli troops from south of Lebanon.
- May 25 is the May Revolution (or Revolución de Mayo), a national holiday in Argentina.
- May 25 is Towel Day, in tribute to Douglas Adams, author of The Hitchhiker's Guide to the Galaxy.
- May 28 is Republic day of Nepal- May 28, 2008.
- May 28 is Armenia's first independence, from the Ottoman Empire;- May 28, 1918.
- Under the French Ancien Régime, it was of habit to "plant a May" or a "tree of May" in the honor of somebody. The County of Nice saw girls and boys "turn the May" with the sound of fife and drum, i.e. to dance rounds of May around the tree of May planted on the place of the village.
- The second Sunday in May is Mother's Day in the United States.
- Each year in May, the Eurovision Song Contest is held.
- The Indianapolis 500 is held on the Sunday before Memorial Day.
- In Canada, Victoria Day is celebrated on the last Monday on or before May 24.
- The last Monday of May is Memorial Day in the United States, first celebrated on May 5, 1866, in Waterloo, New York.
Monthlong events in May
- Haitian Heritage Month
- Asthma Awareness Month
- Celiac Awareness Month
- May is National Stroke Awareness Month
- May is Better Speech and Hearing Month. (From an SLP person with their master's degree)
- May is Cystic Fibrosis Awareness Month. 
- May is Pet Cancer Month.
- May is National Brain Tumor Awareness Month. (http://www.MilesForHope.org)
- May is Systemic Lupus Erythematosus Awareness Month.
- South Asian Heritage Month – celebration of Indian/South Asian peoples and peoples of Indian/South Asian descent worldwide
- Asian Pacific American Heritage Month – celebration of Asian and Pacific Islanders in the United States.
- Jewish American Heritage Month – celebration of Judaism in the United States.
- Mental Health Awareness Month – raising awareness about mental illness in the United States.
- National Military Appreciation Month – in the United States to recognize and honor the US Armed Forces.
- Skin Cancer Awareness Month
- May is traditionally devoted to the Blessed Virgin Mary in Roman Catholic traditions. May crowning occurs in some locales at the beginning of the month.
- In New Zealand, May is the New Zealand Music Month.
- Older Americans Month in the United States, established by John F. Kennedy in 1963.
- National Moving Month in the United States – recognizing America's mobile roots and kicking off the busiest moving season of the year.
- National Smile Month in the United Kingdom
- May is National amyotrophic lateral sclerosis (ALS, also known as Lou Gehrig’s Disease) Awareness Month in the United States.
- National Bike Month in the United States
- May is Drinking Water Month in the United States and Canada
- May is National Masturbation Month in the United States – a day out of the month is chosen for National Masturbation Day
- National Foster Care Month 
- National Electrical Safety Month 
- Garden for Wildlife month 
- International Mediterranean Diet Month 
- National Burger Month 
- Hepatitis Awareness Month 
- World Trade Month 
- Zombie Awareness Month 
- National Osteoporosis Month 
- National Pet Month 
- National Water Safety Month 
- National Golf Month 
- International Internal Audit Awareness Month 
- International Drum Month, Moved from November to May!
Weeklong events in May
1st Week of May
- New Zealand Sign Language Week happens once every year in May, Deaf Aotearoa New Zealand organises NZSL Week with over 500 events happening in New Zealand to help promote the language as well as raise awareness about New Zealand’s Deaf community.
2nd Week of May
- Bike Week (Bicycle Week) is a yearly international event that advocates the importance of bicycling as a means of transportation. Bike Week takes place during the second week of May or June and is typically an entire week of city-wide cycling supplemented with events.
3rd Week in May
- The League of American Bicyclists is promoting Bike-to-Work Week from May 14 to 18, 2012 and Bike-to-Work Day on Friday, May 18, 2012.
Last Week in May
- ALIA celebrates Library and Information week in May. Events are organised by libraries around Australia to encourage people to use their local libraries. Children's librarians hold a special event known as National Simultaneous Storytime, where public and school libraries read the same book, at 11 am EST, to children around Australia.
- International Headband Week runs from the Monday-Friday in the last week of May. People all around the world are encouraged to wear Headbands to work and other social events to promote character building and confidence in the workplace and other social environments.
May moving events
- Eastern Christianity celebrates Easter on a Sunday between April 4 and May 8.
- On the full moon of May, Vesak is celebrated in many southeast Asian countries; it commemorates Siddhartha Gautama.
- In Canada, Victoria Day is observed on the Monday on or before May 24. In Quebec, it is known as Patriots Day.
- Most common day of the year for local and general elections in the United Kingdom
First or second Friday
- In the United States, Military Spouse Day is observed on the Friday preceding Mother's Day.
- Is Mother's Day in 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.
- World Fair Trade Day is celebrated.
- The Preakness Stakes is run, second jewel in the triple crown of horse racing.
- Is Mother's Day in Algeria, Dominican Republic, France, Haiti, Mauritius, Morocco, Sweden, Tunisia.
- Is Children's Day in Hungary.
- In the United States, Memorial Day, a public holiday, is on May 30, but observed on the last Monday in May.
- May's birthstone is the emerald which is emblematic of love and success.
- The May birth flower is the Lily of the Valley and the Crataegus monogyna. It is native throughout the cool temperate Northern Hemisphere in Asia, Europe, and in the southern Appalachian Mountains in the United States, but has been naturalized throughout the temperate climactic world.
- The "mayflower" 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.
- The zodiac signs for the month of May are Taurus (until May 20) and Gemini (May 21 onwards).
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- "Ceremony at "Wedding of the Rails," May 10, 1869 at Promontory Point, Utah". World Digital Library. 1869-05-10. Retrieved 2013-07-20.
- National Military Appreciation Month 2006
- GovTrack.us: Tracking the U.S. Congress
- McGuire, Holly; Keil, Kathryn (2010). Chase's 2010 Calendar of Events. McGraw-Hill Companies, Inc.
- Bike Month Website
- State History Guide