Wikipedia:Main Page history/2019 September 21
From today's featured articleHerbig–Haro objects are bright nebular patches formed when narrow jets of partially ionized gas ejected from newborn stars collide with clouds of gas and dust. Often aligned with a star's rotational axis, they are commonly found in star-forming regions. Most of them lie within a few light-years of the source. They are transient phenomena, lasting around a few tens of thousands of years. They can change visibly over just a few years, as they move rapidly away from their parent star. First observed in the late 19th century by Sherburne Wesley Burnham, Herbig–Haro objects were not recognized as distinct from other emission nebulas until the 1940s. The first astronomers to study them in detail were George Herbig and Guillermo Haro, who independently recognized that the objects were by-products of the star formation process. Although the objects emit visible wavelengths, many are hidden by dust and gas, and can only be seen at infrared wavelengths. (Full article...)
Recently featured:
Did you know...
|
In the news
On this daySeptember 21: International Day of Peace
Andrew II of Hungary (d. 1235) · Polyxena of Hesse-Rotenburg (b. 1706) · Florence Griffith Joyner (d. 1998)
More anniversaries:
|
Today's featured picture
Dried bark strips, bark powder and dried flowers of the small tree Cinnamomum verum. Native to Sri Lanka, C. verum, also known as true cinnamon, is an evergreen of the family Lauraceae. The tree's inner bark is used to make the spice cinnamon, although most of the world's supply comes from several other Cinnamomum species. Sri Lanka produces 80 to 90 per cent of C. verum cinnamon; the tree is also cultivated commercially in the Seychelles and Madagascar. Photograph credit: Simon A. Eugster
Recently featured:
|
Other areas of Wikipedia
- Community portal – Bulletin board, projects, resources and activities covering a wide range of Wikipedia areas.
- Help desk – Ask questions about using Wikipedia.
- Local embassy – For Wikipedia-related communication in languages other than English.
- Reference desk – Serving as virtual librarians, Wikipedia volunteers tackle your questions on a wide range of subjects.
- Site news – Announcements, updates, articles and press releases on Wikipedia and the Wikimedia Foundation.
- Village pump – For discussions about Wikipedia itself, including areas for technical issues and policies.
Wikipedia's sister projects
Wikipedia is hosted by the Wikimedia Foundation, a non-profit organization that also hosts a range of other projects:
Free media repository
Wiki software development
Wikimedia project coordination
Free textbooks and manuals
Free knowledge base
Free-content news
Collection of quotations
Free-content library
Directory of species
Free learning materials and activities
Free travel guide
Dictionary and thesaurus