To report an error when this list is currently on the Main Page, see Main Page errors. Please remember that this list defers to the supporting articles, so it is best to achieve consensus and make any necessary changes there first.
Before making a suggestion, please read the selected anniversaries guidelines. Please remember that this list usually defers to supporting pages when there is disagreement, so it is best to achieve consensus and make any necessary changes there first.
Q1: Why is [Insert event here], an event that is "more important and significant" than all the others that are currently listed, not posted?
A1: Relative article quality along with the mix of topics already listed are often deciding factors in what gets posted. Any given day of the year can have a great many important or significant historical events. The problem is that there is generally only room on the Main Page to list about 5 events at a time, so not everything can be posted.
As stated on Wikipedia:FAQ/Main Page, the items and events posted on the Main Page are chosen based more on how well they are written, not based on how much important or significant their subjects are. It is easier for admins to select a well-written, cited, verifiable article over a poor one versus trying to determine objectively how much a subject is important or significant.
Keep in mind that the quality requirements only apply to the selected bolded article, not the other links. Thus, an event may qualify for multiple dates in a year if there is an article written in a summary style and an article providing detailed content; if one of those pages have cleanup issues, the other page can be bolded as an alternate.
Another criterion is to maintain some variety of topics, and not exhibit, just for example, tech-centrism, or the belief that the world stops at the edge of the English-speaking world. Many days have a large pool of potential articles, so they will rotate in and out every year to give each one some Main Page exposure. In addition, an event is not posted if it is also the subject of this year's scheduled featured article or featured picture.
Q2: There are way too many 20th-century events listed. Why aren't there more events from the 19th century and before?
Q3: This page seems to be biased toward events based in [Insert country or region here]. What can be done about it?
A3: This again is attributed to the systemic bias of Wikipedia. Many users are generally more interested in working on good, well-written articles pertaining to their home country. Since this is the English Wikipedia, there will be more English-speaking users, and thus more articles pertaining to English-speaking countries. And if there are more users who are from the United States, there will probably be more well-written articles about events based in the United States. Again, if you would like to further help mitigate the systemic bias in Wikipedia, see Wikipedia:WikiProject Countering systemic bias.
Q4: Why is the birthday of [Insert name here] not listed?
A4: Births and deaths can only be used on centennials, etc. Exceptions can be made if they are directly related to assassinations, executions, natural disasters, civil accidents, genocide/extinction, or other historically significant topics that frequently appear on the Selected Anniversaries pages.
Q5: Are the holidays/observances listed in any particular order?
A5: Yes, there is a specified order: International observances first, then alphabetically by where observed. But this is a recent change (1 June 2011), so not every page has been updated to reflect this.
Q6: Some of the holidays/observances that are listed have dates in parentheses beside them. What do they mean?
A6: There are two reasons that some holidays/observances have dates next to them:
Non-Gregorian-based holidays/observances are marked with the current year as a reminder to others that their dates do in fact vary from year to year.
National Days, Independence Days, and other holidays celebrating the nationhood of a country are generally marked by the year of the significant historic date being observed.
Included: Battle of Glasgow (2nd appearance, last in 2009; 150th anniversary); Dreyfus affair (first appearance; blurb previously featured Alfred Dreyfus which is currently ineligible and is making its 4th appearance, last in 2006; rescued from Ineligible); Mata Hari (7th appearance, last in 2011); Hurricane Hazel (2nd appearance, last in 2010; 60th anniversary; rescued from Ineligible)
Repeats: Edward Gibbon (3rd consecutive appearance, 3 total; 250th anniversary)