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View Full Version : 4 Lunar Phases: 1st Quarter, Full Moon, 3rd Quarter, New Moon; each is ~7.4 days long



Brad Watson
2014-May-16, 04:19 PM
I've encountered many 'experts' who incorrectly state that the "4 phases of the Moon are New Moon, 1st Quarter, Full Moon, Last Quarter". 3rd Grade math has us place 1st Quarter first. The 2nd Quarter is the Full Moon. The 3rd Quarter is just that; it certainly is not the "Last Quarter"! And the 4th Quarter/Last Quarter is the New Moon. Hence, the 4 lunar phases are 1st Quarter, Full Moon, 3rd Quarter, New Moon. Ironically, I've seen astrologers get this right while professional astronomers get it wrong even in college textbooks! When the 4 Lunar Phases are divided into the 8 Lunar Phases, almost everyone starts their chart with the New Moon. Ok, but that's the '4th Quarter' or 'Last Quarter'. http://en.wikipedia.org/wiki/Lunar_phases

Lunar 'moonths' are 29.53 days long, therefore the 4 phases are roughly 7 days (~7.4 days) each varying due to apogee and perigee. This is where the 7 Day Creation Story of Genasis emanates from; the 4 lunar phases is where the 7 day week and 4 weeks in a month originated. The ancients didn't do fractions. They would keep track of the lunar months by alternating between 29 and 30 day cycles. At Stonehenge, there was one circle of 29 posts and another of 30. Lunar calendars like the Hebrew and Arabic Calendars alternate between 29 and 30 days. http://en.wikipedia.org/wiki/Arabic_calendar

The lunar year is 12 lunar months and ~354 days (29.53 x 12) long. Lunar year + 7 day week + 4 days = 365 day solar year. Every 19 years, the synodic (lunar) month and solar year align, i.e. a Full Moon on July 4th (7/4) won't reoccur again for 19 years. This is known as the Metonic Cycle. http://en.wikipedia.org/wiki/Metonic_cycle

Hornblower
2014-May-16, 06:13 PM
I've encountered many 'experts' who incorrectly state that the "4 phases of the Moon are New Moon, 1st Quarter, Full Moon, Last Quarter". 3rd Grade math has us place 1st Quarter first. The 2nd Quarter is the Full Moon. The 3rd Quarter is just that; it certainly is not the "Last Quarter"! And the 4th Quarter/Last Quarter is the New Moon. Ironically, I've see astrologers get this right while professional astronomers get it wrong even in college textbooks! When the 4 Lunar Phases are divided into the 8 Lunar Phases, almost everyone starts their chart with the New Moon. Ok, but that's the '4th Quarter' or 'Last Quarter'. http://en.wikipedia.org/wiki/Lunar_phases

Lunar 'moonths' are 29.5 days long, therefore the 4 phases are roughly 7 days (~7.4 days) each. This is where the 7 Day Creation Story of Genasis emanates from; the 4 lunar phases is where the 7 day week and 4 weeks in a month originated. The ancients didn't do fractions. They would keep track of the lunar months by alternating between 29 and 30 day cycles. At Stonehenge, there was one circle of 29 posts and another of 30. Lunar calendars like the Hebrew and Arabic Calendars alternate between 29 and 30 days. http://en.wikipedia.org/wiki/Arabic_calendar

The lunar year is 12 lunar months and 354 days (29.5 x 12) long. Lunar year + 7 day week + 4 days = 365 day solar year. Every 19 years, the lunar and solar year align, i.e. a Full Moon on July 4th (7/4) won't reoccur again for 19 years. This is known as the Metonic Cycle. http://en.wikipedia.org/wiki/Metonic_cycle

There is nothing inherently "correct" or "incorrect" about the choice of a standard reference point for reckoning the monthly cycle. Any point that is convenient for the task at hand will do. People who use the actual lunar cycle for the basis of their religious calendars, such as the Jews and the Muslims, mark the start of a new month shortly after New Moon, when a thin crescent becomes visible under good conditions.

Let's face it. Astronomers use quite a few questionable choices of words in their scientific jargon, some of which are holdovers from archaic common practice and/or superseded theories. The use of "last quarter" for the waning half Moon appears analogous to the old-fashioned timekeeping jargon of "quarter past 12" for 12:15 and "quarter 'til 1" for 12:45, to give numerical examples. The waxing half Moon marks the end of the first quarter of a month since the most recent new Moon, and the waning half Moon marks the beginning of the last quarter before the next new Moon.

Brad Watson
2014-May-16, 09:15 PM
Hornblower,

Wrong. Your analogy of 12:45 is often called, "Three quarters past 12". Using your illogic, we should call 12:45, "The Last quarter before 1". You would then 1, "The beginning of the 1st Quarter"? No.

Everyone calls the 4th Quarter the "Last Quarter", i.e. football, basketbol, hockey. And the 3rd Quarter is always called the "3rd Quarter". If an astronomer is using incorrect terms, they need to be corrected.


- Drum Beater

Hornblower
2014-May-16, 10:24 PM
Hornblower,

Wrong. Your analogy of 12:45 is often called, "Three quarters past 12". Using your illogic, we should call 12:45, "The Last quarter before 1". You would then 1, "The beginning of the 1st Quarter"? No.

Everyone calls the 4th Quarter the "Last Quarter", i.e. football, basketbol, hockey. And the 3rd Quarter is always called the "3rd Quarter". If an astronomer is using incorrect terms, they need to be corrected.


- Drum Beater

I agree that "last quarter" for the waning half Moon is a lousy choice of words in a mathematical sense, but I think it is a trifle compared with the use of "early" and "late" for stellar spectral types or spiral galaxy forms, or calling carbon, nitrogen, oxygen or silicon "metals".

Squink
2014-May-17, 01:34 PM
Should call em first half and last half. This quarter stuff is just nonsense, with the moon appearing visually full for only 3 days, and visually new for less than a day. Waxing and waning works well enough, with the special days full and new.

Brad Watson
2014-May-18, 08:30 PM
Hornblower,

So you'll 'blow your horn' while I 'beat the drum' for the 4 Lunar Phases: 1st Quarter, Full Moon, 3rd Quarter, New Moon?

Hornblower
2014-May-18, 11:00 PM
Hornblower,

So you'll 'blow your horn' while I 'beat the drum' for the 4 Lunar Phases: 1st Quarter, Full Moon, 3rd Quarter, New Moon?

Yes, provided we insert an adjective such as "principal" between 4 and Lunar. There are infinitely many phases between one New Moon and the next. The half and full phases, marking quarters of a revolution, simply are convenient visual benchmarks.

Ara Pacis
2014-May-23, 08:50 AM
I dunno, but I call the waxing crescent as the first quarter, the waxing gibbous as the second quarter, the waning gibbous as the third quarter, and the waning crescent as the fourth or last quarter.

Brad Watson
2014-Jul-04, 07:47 PM
Yes, provided we insert an adjective such as "principal" between 4 and Lunar. There are infinitely many phases between one New Moon and the next. The half and full phases, marking quarters of a revolution, simply are convenient visual benchmarks.
Hornblower,

That's unnecessary. 4 Lunar Phases carries the insinuation that they are the 4 principal lunar phases. Ok then, 4 lunar phases: 1st Quarter, Full Moon, 3rd Quarter, New Moon.

Brad Watson
2014-Jul-04, 07:50 PM
Everyone,

I tweaked the op by adding that "the 4 lunar phases are roughly 7 days (~7.4 days) each varying due to apogee and perigee.

grapes
2014-Jul-05, 01:40 AM
Everyone calls the 4th Quarter the "Last Quarter", i.e. football, basketbol, hockey. And the 3rd Quarter is always called the "3rd Quarter". If an astronomer is using incorrect terms, they need to be corrected.

I call the New Moon the 0th Quarter, for obvious reasons. :)

Jeff Root
2014-Jul-05, 09:53 AM
Brad,

How do you deal with the fact that 1/4 moon = 1/2 moon?

-- Jeff, in Minneapolis

Jeff Root
2014-Jul-05, 09:58 AM
Brad,

You are confusing an interval of time with a point in time.
They are different things. A quarter of a football game is
an interval of time. A Quarter Moon is a point in time.

-- Jeff, in Minneapolis

.

Brad Watson
2014-Jul-05, 11:38 AM
Should call em first half and last half. This quarter stuff is just nonsense, with the moon appearing visually full for only 3 days, and visually new for less than a day. Waxing and waning works well enough, with the special days full and new.

Squink,

No, the 4 lunar phases are NOT nonsense and it's been referred to for thousands of years by billions of observers. The lunar month of 29.53 days has 4 phases roughly 7 days (~7.4 days) each varying due to apogee and perigee. The ancients didn't do fractions and didn't know about apogee and perigee. Lunar months became the basis of the lunar calendar with alternating 29-day and 30-day months. 7-day-weeks are observed worldwide and have great historical influence, i.e. Genasis Creation Story of 7 days, 7th day Sabbath.

Brad Watson
2014-Jul-05, 12:10 PM
The ancients observed the heavens and seasonal changes. They began to count the days in the lunar months: alternating between 29 or 30 days. The ancients didn't do fractions, therefore they didn't recognize the lunar month as being 29.53 days. They recognized that there are 4 lunar phases: 1st Quarter, Full Moon, 3rd Quarter, New Moon and they recognized that each phase is a little more than 7 days (~7.4 days) each. The 7-day cycle was recognized as the week and this famously was used in the Hebrew Creation Story in Genasis. The ancients observed that there was a 12-month lunar year and they observed that this could not be relied on to keep track of the perceived 4 seasons. The Egyptians especially observed that the lunar calendar alone could not be relied on to accurately keep track of the periodic flooding of the Nile River. The ancient Mesopotamians were the first (c. 4000 BC) to keep astronomical/astrological records. They built their ziggurats (observatories/temples) to be 7 levels high so as to reflect the 7 moving objects seen in the heavens with the naked eye (7 Classical Planets): Moon, Mercury, Venus, Sun, Mars, Jupiter, and Saturn. The Mesopotamians first kept track of the 4 seasons. This information was vital to their farming. Around the same time, the Egyptians also recorded the solar year and could now predict the annual flooding of the Nile and use this information to aid their farming. One way to think of the relationship between the lunar year and solar year was to take the lunar year of 354 days add a 7 day week plus 4 days and you have the solar year.

Shaula
2014-Jul-05, 02:33 PM
The ancients didn't do fractions...
They did from about 1800BC. The Egyptians, Babylonians, Indian and Greek civilisations all used them for example.

Ara Pacis
2014-Jul-05, 02:54 PM
They did from about 1800BC. The Egyptians, Babylonians, Indian and Greek civilisations all used them for example.

Thank goodness for that, otherwise humanity would never have developed pie or pizza. :)

Ara Pacis
2014-Jul-05, 02:58 PM
But 4 days is a fraction of a week, but if they didn't do fractions...

Shaula
2014-Jul-05, 03:44 PM
Thank goodness for that, otherwise humanity would never have developed pie or pizza. :)
I get this image of four people in loincloths looking at a deer they caught. "There is one deer but four of us. How can we all eat?" "I don't know. We have no concept of subdivision. There are four of us but one deer. This is impossible." "Hang on a minute... I think... YES! I have invented fractions. We will not starve due to our inability to divide our catches!"

Swift
2014-Jul-05, 07:20 PM
Everyone,

I tweaked the op by adding that "the 4 lunar phases are roughly 7 days (~7.4 days) each varying due to apogee and perigee.
Brad Watson,

Don't do that again. Going back and editing a six week old post is considered revisionism and is a very serious rule violation (Rule 11). Please don't do that in the future.

tusenfem
2014-Jul-05, 07:23 PM
essentially same threads merged

Jerry
2014-Jul-05, 08:03 PM
If there is anything silly about this whole thread, it is the use of the term 'new moon'. There is no such thing; and the division of the quarters and names are quite arbitrary. As a kid, I thought a 'full moon' and a 'new moon' where the same - a newly completed moon.

Astronomers are quite notorious for using archaic, historical and field-specific terms rather than creating simple systems. The rings of Saturn and stellar evolution are good examples of poor nomenclature decisions. But you will never convince an astronomer the correct order of Saturn's rings is ABCDEFGH...

tusenfem
2014-Jul-05, 09:44 PM
... But you will never convince an astronomer the correct order of Saturn's rings is ABCDEFGH...

ah tooooo boring!
Oh Be A Fab Guy Kiss Me
who ever decided on the orderof the alphabet anyway ...

Shaula
2014-Jul-06, 05:27 AM
Astronomers are quite notorious for using archaic, historical and field-specific terms rather than creating simple systems. The rings of Saturn and stellar evolution are good examples of poor nomenclature decisions. But you will never convince an astronomer the correct order of Saturn's rings is ABCDEFGH...
In both those examples the apparent complexity is simply due to evolution. The original stellar classification order was ABC... based on the amount of hydrogen in their spectrum. Later it became apparent that in fact temperature was a more logical way to order the stars. There was already a numeric system (the MKK system) so there was basically a choice. Rename the classes so when you read a paper from prior to about 1905 you had to remember that now what they called A was in fact O, B was A and so on. And then when new stellar types were declared rejig it again so now a pre-1930 A is called a W ... ... or you could accept that the system was not in alphabetical order.

As for Saturn it was even easier. Originally 3 sections were known, A B C. More were found. Again, should we have changed the names so prior to 1979 the A ring referred to what we now call F etc etc? That would be confusing.

Imagine the confusion it would cause if we named all the countries on Earth A, B , C and so on starting with the furthest west. So in 1490 West Africa is A, Portugal is B, Ireland is C. Then Columbus happens. So now in 1492 Jamaica is A, West Africa is B, Portugal is C. In 1498 Venezuela is A ... ... Now is the ostensibly simple system actually simpler to use?

ngc3314
2014-Jul-06, 05:54 PM
Astronomers are quite notorious for using archaic, historical and field-specific terms rather than creating simple systems. The rings of Saturn and stellar evolution are good examples of poor nomenclature decisions. But you will never convince an astronomer the correct order of Saturn's rings is ABCDEFGH...

Yeah, we get dumped on a lot for this. But in a Universe where discovery unfolds at its own, what else should we do? Rename all Saturn's rings every time new technology finds another outer or intervening low-density rings? At what point are we justified in in taking Type Ia supernovae (which as a class have well-defined criteria which can be applied to data independent of the level of theoretical understanding) and calling them white-dwarf supernovae (skipping the question of whether that's one or two)? (This happens now, BTW, in a lot of introductory textbooks, a context where most of us have studiously deleted the magnitude scale as well for introducing confusion for no useful gain). Of course practitioners (in almost any specialist field with a long history) parse phrases whereas neophytes look at words - I certainly no longer separate "planetary nebula" or "open cluster" , for example.

Astronomers are not completely immune to change - with only moderate pain, the galactic coordinate system was revised once the IAU was pretty sure that we knew where the centre of the Galaxy is, so the zero point of longitude made physical sense. I can remember when careful discussions still used superscript I or II to be sure which system was in use. A nomenclatural shift needs to be worth the disruption and confusion it will cause in the short term (do I need to cite any more recent examples?)

Jerry
2014-Jul-07, 12:20 AM
Assuming the original choices were in some kind of order, a decimal system would work: -A.2, -A.1, A.0 A.1 A.12 A.2 Or you could add addition rings with flats and sharps like Beethoven did A- A+ B- B+ He didn't stick a H between C and D because he knew music was hard enough already.

Since temperatures are now used for stars, there are plenty of colors to go around, or why not just a 200K Kelvin star?

Swift
2014-Jul-07, 02:20 AM
I think we have enough examples of nomenclature in other systems, both astronomical and otherwise. Let's get back to the OP's ideas about the phases of the moon. Thanks,

Brad Watson
2014-Jul-07, 12:39 PM
I call the New Moon the 0th Quarter, for obvious reasons. :)
grapes,

Seriously, the "0th Quarter"? No one will agree with that ridiculous term.

Why can't you simply agree with the 4 phases of the Moon: 1st Quarter, Full Moon, 3rd Quarter, New Moon. Most people agree with this very simple and logical terminology.

Strange
2014-Jul-07, 12:45 PM
Seriously, the "0th Quarter"? No one will agree with that ridiculous term.

We already have a 0th law of thermodynamics (and robotics?), so it doesn't seem unreasonable.


Why can't you simply agree with the 4 phases of the Moon: 1st Quarter, Full Moon, 3rd Quarter, New Moon. Most people agree with this very simple and logical terminology.

Most people?

Anyway, arguing to change the conventional starting point is a bit of a lost cause. You might as well argue that electrons should be defined to have a positive charge or that the value of pi should be doubled.

Brad Watson
2014-Jul-07, 12:47 PM
They did from about 1800BC. The Egyptians, Babylonians, Indian and Greek civilisations all used them for example.
Shaula,

"1800 BC"? Please provide a source/link for that. Even if that date is accurate, before that "the ancients did not use fractions" is correct. In tracking the lunar months, they alternated between 29 & 30 days and the Hebrew, Arabic, and Chinese Calendars still do.

Brad Watson
2014-Jul-07, 12:49 PM
We already have a 0th law of thermodynamics (and robotics?), so it doesn't seem unreasonable.

Most people?

Anyway, arguing to change the conventional starting point is a bit of a lost cause. You might as well argue that electrons should be defined to have a positive charge or that the value of pi should be doubled.

I agree, you are Strange.

Hornblower
2014-Jul-07, 12:49 PM
grapes,

Seriously, the "0th Quarter"? No one will agree with that ridiculous term.

Why can't you simply agree with the 4 phases of the Moon: 1st Quarter, Full Moon, 3rd Quarter, New Moon. Most people agree with this very simple and logical terminology.
My underscore. Once again, the set of phases of the Moon includes those four familiar benchmarks but is not limited to them. A crescent or gibbous of any magnitude is a phase in the sense that is being used geometrically. Technically, phase is the angle between the line of conjunction with the Sun and the current Earth-Moon line.

If anyone thinks I am being verbally pedantic, please fire away.

Brad Watson
2014-Jul-07, 12:53 PM
I dunno, but I call the waxing crescent as the first quarter, the waxing gibbous as the second quarter, the waning gibbous as the third quarter, and the waning crescent as the fourth or last quarter.

Ara Pacis,

Please keep your posts ON-TOPIC. You agree with the obvious: the 4th quarter is the last quarter. Anyone who disagrees with this should be forced to take 3rd Grade math again.

Brad Watson
2014-Jul-07, 12:56 PM
If there is anything silly about this whole thread
Jerry,

No, there is NOT anything silly about using the correct names of the 4 phases of the Moon: 1st Quarter, Full Moon, 3rd Quarter, New Moon. This should be obvious to all those who think logically. I think those that are arguing here just like to argue.

Brad Watson
2014-Jul-07, 01:00 PM
My underscore. Once again, the set of phases of the Moon includes those four familiar benchmarks but is not limited to them. A crescent or gibbous of any magnitude is a phase in the sense that is being used geometrically. Technically, phase is the angle between the line of conjunction with the Sun and the current Earth-Moon line.

If anyone thinks I am being verbally pedantic, please fire away.
Hornblower,

I think you are being verbally pedantic. Please STOP!

Brad Watson
2014-Jul-07, 01:06 PM
Brad,

How do you deal with the fact that 1/4 moon = 1/2 moon?

-- Jeff, in Minneapolis
Jeff,

I never said that "1/4 moon = 1/2 moon" and I've never seen that anywhere before until now. Are you trying to intentionally confuse things? If so, why? Please STOP! It's very simple...

There are 4 primary lunar phases: 1st Quarter, Full Moon, 3rd Quarter, New Moon.

Swift
2014-Jul-07, 01:41 PM
Ara Pacis,

Please keep your posts ON-TOPIC. You agree with the obvious: the 4th quarter is the last quarter. Anyone who disagrees with this should be forced to take 3rd Grade math again.



Jerry,

No, there is NOT anything silly about using the correct names of the 4 phases of the Moon: 1st Quarter, Full Moon, 3rd Quarter, New Moon. This should be obvious to all those who think logically. I think those that are arguing here just like to argue.


Hornblower,

I think you are being verbally pedantic. Please STOP!
Brad Watson,

Three posts in a row, each worthy of an infraction.

Do not play Moderator, by telling other people what they may or may not post. If you think someone's post is inappropriate, you Report it (black triange with the ! in the lower left of every post) and let the Moderation Team deal with it. And you do not question other members' logic or their motives for posting; that's inpolite.

Jeff Root
2014-Jul-07, 02:47 PM
Jeff,

I never said that "1/4 moon = 1/2 moon" and I've never
seen that anywhere before until now.
Really? It is pretty obvious, and should have been obvious
to you long ago if you have given the phases of the Moon
a significant amount of thought. A Quarter Moon is a Half
Moon. And vice-versa. I'm not saying that one term is
better than the other, as Squink did in post #5. I'm just
asking you how you deal with it.

So, now that you are aware of it, how do you deal with the
fact that 1/4 moon = 1/2 moon?



Are you trying to intentionally confuse things?
Certainly not. I'm trying to help you better understand a
subject that you are evidently interested in: nomenclature
for the phases of the Moon.

-- Jeff, in Minneapolis

Hornblower
2014-Jul-07, 02:53 PM
Jeff,

I never said that "1/4 moon = 1/2 moon" and I've never seen that anywhere before until now. Are you trying to intentionally confuse things? If so, why? Please STOP! It's very simple...

There are 4 primary lunar phases: 1st Quarter, Full Moon, 3rd Quarter, New Moon.My underscore. The simple addition of that adjective primary completely resolves my misgivings about your earlier remarks. I stand by my opinion that phase is a legitimate term for the illumination-angle-related shape and extent of the visible illuminated portion at any position in the monthly cycle.

grapes
2014-Jul-07, 06:12 PM
I call the New Moon the 0th Quarter, for obvious reasons.

grapes,

Seriously, the "0th Quarter"? No one will agree with that ridiculous term.

It's not ridiculous. Others have given similar examples too.


Why can't you simply agree with the 4 phases of the Moon: 1st Quarter, Full Moon, 3rd Quarter, New Moon. Most people agree with this very simple and logical terminology.
But I agree with that.

So does the Wikipedia article on the phases of the moon. It just points out that it is common usage to call the third quarter "the last quarter".

The verbal problem that you haven't addressed is whether the "new moon" phase starts a new sequence or ends the sequence. Under your scheme, it does not. Wouldn't it be better to list the phases as new moon, first quarter, full moon, third quarter? That way, it starts with "new moon".

That does make the third quarter the last quarter, though.

Shaula
2014-Jul-07, 07:34 PM
Shaula,

"1800 BC"? Please provide a source/link for that. Even if that date is accurate, before that "the ancients did not use fractions" is correct. In tracking the lunar months, they alternated between 29 & 30 days and the Hebrew, Arabic, and Chinese Calendars still do.
http://nrich.maths.org/2515 - 1800BC
http://en.wikipedia.org/wiki/Fraction_%28mathematics%29#History - at least by 1000BC
http://mitpress.mit.edu/books/mathematics-time-pharaohs - showing what the Egyptians did
http://www.basic-mathematics.com/history-of-fractions.html - 1600BC and a reference to Papyrus source

Hornblower
2014-Jul-07, 09:45 PM
It's not ridiculous. Others have given similar examples too.

But I agree with that.

So does the Wikipedia article on the phases of the moon. It just points out that it is common usage to call the third quarter "the last quarter".

The verbal problem that you haven't addressed is whether the "new moon" phase starts a new sequence or or ends the sequence. Under your scheme, it does not. Wouldn't it be better to list the phases as new moon, first quarter, full moon, third quarter? That way, it starts with "new moon".

That does make the third quarter the last quarter, though.
In a purely mathematical sense, a chosen point can simultaneously end one cycle and start a new one in any cyclical phenomenon. We can choose whatever point and give it whatever name we wish according to what is useful for the task at hand.

Brad Watson
2014-Jul-09, 10:27 PM
Hornblower,

If one starts with the New Moon, they will see the Full Moon in roughly 14 days: two weeks. This cycle was obvious to the ancients and they divided the lunar cycle into 4 phases each being slightly over 7 days (~7.4 days) each. But we should recognize the natural order of 1st Quarter, Full Moon, 3rd Quarter, New Moon.

grapes
2014-Jul-10, 04:51 AM
Hornblower,

If one starts with the New Moon, they will see the Full Moon in roughly 14 days: two weeks. This cycle was obvious to the ancients and they divided the lunar cycle into 4 phases each being slightly over 7 days (~7.4 days) each. But we should recognize the natural order of 1st Quarter, Full Moon, 3rd Quarter, New Moon.
If you start with 1st quarter, you see the full moon in seven days.

It makes sense to start the new sequence with a new moon, no?

Hornblower
2014-Jul-11, 12:26 PM
Hornblower,

If one starts with the New Moon, they will see the Full Moon in roughly 14 days: two weeks. This cycle was obvious to the ancients and they divided the lunar cycle into 4 phases each being slightly over 7 days (~7.4 days) each. But we should recognize the natural order of 1st Quarter, Full Moon, 3rd Quarter, New Moon. I agree, those are good choices of words for the respective points in the monthly cycle, and the sequence is mathematically consistent. I previously have said that the colloquial "last quarter" for the third quarter is mathematically lousy. Are you disagreeing with me on some point or am I overthinking your remarks?

Hornblower
2014-Jul-11, 12:41 PM
If you start with 1st quarter, you see the full moon in seven days.

It makes sense to start the new sequence with a new moon, no?
It made sense to the ancient Babylonians, Jews, Muslims, etc. to use the date of the first visible evening crescent as the start of a new month for religious and other civil purposes. That usually placed the moment of geometric full Moon sometime during the 14th day. The timing could have been off a bit in September, especially in years in which the Moon's path was well south of the Sun, at which time the visibility conditions for the emerging crescent were at their worst.

Jeff Root
2014-Jul-11, 12:59 PM
There are only two quarter moons, conventionally called
"First Quarter" and "Third Quarter" (or Last Quarter").
They are just names. My name is "Jeff". It isn't logical,
it is just a name. First Quarter can also be called "First
Half" and Third Quarter can also be called "Second Half".
Those names work just as well and their meanings are
equally clear.

The names refer to the appearance of the Moon at the
given point in time, not to the intervals between those
points.

-- Jeff, in Minneapolis

DaveC426913
2014-Jul-11, 02:04 PM
I have always under the impression that the New Moon starts each cycle. Afterall, it's new, not ending or dying.

That being the case: you get new Moon, 1st quarter, full, last quarter (third quarter works, but is more ambiguous that simply 'last').

Ara Pacis
2014-Jul-11, 06:05 PM
The New moon and Full moon, as well as the quarters (half disk illumination) are specific observations lasting from seconds to hours to a day or so. The moon obviously doesn't stay that way. So, I suggest we don't name week-long periods after them.

When will the IAU get on this and make a definition of the monthly phases?

Hornblower
2014-Jul-12, 11:25 PM
The New moon and Full moon, as well as the quarters (half disk illumination) are specific observations lasting from seconds to hours to a day or so. The moon obviously doesn't stay that way. So, I suggest we don't name week-long periods after them.

When will the IAU get on this and make a definition of the monthly phases?
I think your naming-after line of thought is backward. Any ancient observer could have seen that the week-long period from conjunction with the Sun was about one quarter of the lunar month. Calling the waxing visual half phase "first quarter" could be shorthand for "the phase that marks the completion of the first quarter of the month."

Hornblower
2014-Jul-12, 11:27 PM
The New moon and Full moon, as well as the quarters (half disk illumination) are specific observations lasting from seconds to hours to a day or so. The moon obviously doesn't stay that way. So, I suggest we don't name week-long periods after them.

When will the IAU get on this and make a definition of the monthly phases?No such action is needed for calculating a good ephemeris of the Moon.

Ara Pacis
2014-Jul-13, 07:00 AM
I think your naming-after line of thought is backward. Any ancient observer could have seen that the week-long period from conjunction with the Sun was about one quarter of the lunar month. Calling the waxing visual half phase "first quarter" could be shorthand for "the phase that marks the completion of the first quarter of the month."

So.... are you agreeing with me? I'm referring to new moon to half-illumination as first quarter of the month.

Ara Pacis
2014-Jul-13, 07:01 AM
No such action is needed for calculating a good ephemeris of the Moon.

Other definition issues did not revolve around calculating ephemerides.

Hornblower
2014-Jul-13, 09:58 AM
Other definition issues did not revolve around calculating ephemerides.
But they did involve the classification of various types of bodies, which is not an issue here.

Ara Pacis
2014-Jul-13, 07:02 PM
But they did involve the classification of various types of bodies, which is not an issue here.

But it does involve the visibility of various types of body, which is the mainstay of astronomy.

Brad Watson
2014-Sep-01, 03:24 PM
No such action is needed for calculating a good ephemeris of the Moon.
Horn blower,

What does ephemeris mean? (My BIG dictionary is across the room.)

glappkaeft
2014-Sep-01, 04:30 PM
Have you tried Google?

walker1001
2014-Sep-01, 09:24 PM
Opinions vs factual use??

http://en.wikipedia.org/wiki/New_moon


In astronomy, new moon is the first phase of the Moon, when it lies closest to the Sun in the sky as seen from the Earth. More precisely, it is the instant when the Moon and the Sun have the same ecliptical longitude [1] The Moon is not normally visible at this time except when it is seen in silhouette during a solar eclipse. See the article on phases of the Moon for further details.

and

http://en.wikipedia.org/wiki/Lunar_phase


The four principal lunar phases are first quarter, full moon, third quarter, and new moon (third quarter moon is also known as last quarter moon.) Each of the four lunar phases is roughly 7 days (~7.4 days) each, but varies slightly due to lunar apogee and perigee.

This is true for the use in five other languages, and I would guess in most of the world's languages and unlikely to be changed to any method proposed or believed to be better/"true"/more logical that is proposed on this forum.

antoniseb
2014-Sep-01, 10:32 PM
... What does ephemeris mean? (My BIG dictionary is across the room.)
I'm closing this thread. It is pseudo science from someone too lazy to look up obvious words for himself/herself.