|
Top Document: [sci.astro] Time (Astronomy Frequently Asked Questions) (3/9) Previous Document: C.07.2 Can I calculate the date of Easter? Next Document: C.09 What is the Green Flash (or Green Ray)? See reader questions & answers on this topic! - Help others by sharing your knowledge Jay Respler <jrespler@superlink.net> Colloquially the term "blue moon" is used to mean "a very long time." In fact, there have been at least seven different uses of the term "blue moon" in the past several hundred years. The alt.usage.english FAQ discusses these different meanings of the term "blue moon." The two definitions most relevant to astronomy are the following: 1. Under certain conditions of atmospheric haze, the moon may actually look blue. A notable example occurred after the explosion of the volcano Krakatoa. The appropriate conditions are extremely rare. 2. The second full moon in a calendar month. Since the synodic month is 29.53 days, this kind of blue moon occurs roughly once out of 60 30-day months and once out of 21 31-day months or about once in 2.5 years on average. It can occur in January and the following March if there is no full moon at all in February. There are some indications that some calendars used to put the first moon in the month in red, the second in blue, hence the origin of the term. Philip Hiscock, writing in the 1999 March issue of Sky & Telescope, expands upon the history of this definition. This definition of "blue moon" is of fairly recent vintage and came into widespread use in the late 1980s as a result of the board game Trivial Pursuit. He was able to trace its origin to an (incorrect) entry in the 1937 edition of the _Maine Farmer's Almanac_. The alt.usage.english FAQ is available from <URL: ftp://rtfm.mit.edu/ pub/usenet-by-group/alt.usage.english/alt.usage.english_FAQ> or <URL: http://www.cis.ohio-state.edu/ hypertext/faq/usenet/alt-usage-english-faq/faq.html>. User Contributions:Comment about this article, ask questions, or add new information about this topic:Top Document: [sci.astro] Time (Astronomy Frequently Asked Questions) (3/9) Previous Document: C.07.2 Can I calculate the date of Easter? Next Document: C.09 What is the Green Flash (or Green Ray)? Part0 - Part1 - Part2 - Part3 - Part4 - Part5 - Part6 - Part7 - Part8 - Single Page [ Usenet FAQs | Web FAQs | Documents | RFC Index ] Send corrections/additions to the FAQ Maintainer: jlazio@patriot.net
Last Update March 27 2014 @ 02:11 PM
|
with stars, then every direction you looked would eventually end on
the surface of a star, and the whole sky would be as bright as the
surface of the Sun.
Why would anyone assume this? Certainly, we have directions where we look that are dark because something that does not emit light (is not a star) is between us and the light. A close example is in our own solar system. When we look at the Sun (a star) during a solar eclipse the Moon blocks the light. When we look at the inner planets of our solar system (Mercury and Venus) as they pass between us and the Sun, do we not get the same effect, i.e. in the direction of the planet we see no light from the Sun? Those planets simply look like dark spots on the Sun.
Olbers' paradox seems to assume that only stars exist in the universe, but what about the planets? Aren't there more planets than stars, thus more obstructions to light than sources of light?
What may be more interesting is why can we see certain stars seemingly continuously. Are there no planets or other obstructions between them and us? Or is the twinkle in stars just caused by the movement of obstructions across the path of light between the stars and us? I was always told the twinkle defines a star while the steady light reflected by our planets defines a planet. Is that because the planets of our solar system don't have the obstructions between Earth and them to cause a twinkle effect?
9-14-2024 KP