Advertising R▼
Definition and meaning of 銀河年
Definition
⇨ definition of Wikipedia
Advertizing ▼
Wikipedia
銀河年
銀河年（GY），也稱為宇宙年，是太陽系在軌道上繞著銀河系中心公轉一周的時間[1]，估計在2.25億至2.5億“地球年”之間 [2]。
銀河年相較於地球年（地球在軌道上繞著太陽轉一圈的時間間隔）和月 （月球在軌道上繞著地球轉一圈的時間間隔），可以提供一個更“易於理解”的單位來說明宇宙和地質時代的期間。相較之下，“十億年”(billion years)的尺度對於地質是太大的單位而不適用，“百萬年”(million years)又太小會呈現相當大的數字。[3]。
銀河年的歷史年表
這份年表開始於太陽系的誕生，現在被認為是第20個銀河年。
- 4 GY：地球出現海洋
- 5 GY：生物出現
- 6 GY：原核生物出現
- 7 GY：細菌出現
- 10 GY：穩定的陸地出現
- 13 GY：真核生物出現
- 16 GY：多細胞生物體出現
- 17.8 GY：寒武紀大爆發
- 19 GY：大滅絕
- 19.6 GY：白垩纪-第三纪灭绝事件
- 20.0 GY：現代
相關條目
參考資料
- ^ Astronomy Knowledge Base
- ^ Leong, Stacy. Period of the Sun's Orbit around the Galaxy (Cosmic Year). The Physics Factbook.
- ^ Geologic Time Scale
Template:Time measurement and standards Template:Chronology
|
|||||||||||||||||||||||||||||
sensagent's content
- definitions
- synonyms
- antonyms
- encyclopedia
Webmaster Solution
Alexandria
A windows (pop-into) of information (full-content of Sensagent) triggered by double-clicking any word on your webpage. Give contextual explanation and translation from your sites !
SensagentBox
With a SensagentBox, visitors to your site can access reliable information on over 5 million pages provided by Sensagent.com. Choose the design that fits your site.
Business solution
Improve your site content
Add new content to your site from Sensagent by XML.
Crawl products or adds
Get XML access to reach the best products.
Index images and define metadata
Get XML access to fix the meaning of your metadata.
Please, email us to describe your idea.
Lettris
Lettris is a curious tetris-clone game where all the bricks have the same square shape but different content. Each square carries a letter. To make squares disappear and save space for other squares you have to assemble English words (left, right, up, down) from the falling squares.
boggle
Boggle gives you 3 minutes to find as many words (3 letters or more) as you can in a grid of 16 letters. You can also try the grid of 16 letters. Letters must be adjacent and longer words score better. See if you can get into the grid Hall of Fame !
English dictionary
Main references
Most English definitions are provided by WordNet .
English thesaurus is mainly derived from The Integral Dictionary (TID).
English Encyclopedia is licensed by Wikipedia (GNU).
Copyrights
The wordgames anagrams, crossword, Lettris and Boggle are provided by Memodata.
The web service Alexandria is granted from Memodata for the Ebay search.
The SensagentBox are offered by sensAgent.
Translation
Change the target language to find translations.
Tips: browse the semantic fields (see From ideas to words) in two languages to learn more.
computed in 0.015s