Chatroom
 

If this is your first visit, be sure to check out the FAQ by clicking the link above. You may have to register before you can post: click the register link above to proceed. To start viewing messages, select the forum that you want to visit from the selection below.

Go Back   Bad Astronomy and Universe Today Forum > General > Questions and Answers
Register FAQ Members List Calendar Mark Forums Read

   

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
  #1 (permalink)  
Old 17-August-2006, 10:19 AM
max8166's Avatar
max8166 max8166 is offline
Senior Member
 
Join Date: Oct 2005
Location: Southampton, England
Posts: 227
Cool Where is the moon?

I know the moon circles the earth every 29.5 days, and that it has an eliptical orbit, but how can I find out where it will be? Does it follow the equator in its orbit? The sun has a solstice as the axis of the earth changes over a year but does the moon have a solstice too?

Is the information in here http://en.wikipedia.org/wiki/Moon ?
And Here http://en.wikipedia.org/wiki/Ecliptic#Ecliptic_and_Moon ?

Last edited by max8166; 17-August-2006 at 11:05 AM.
Reply With Quote
  #2 (permalink)  
Old 17-August-2006, 11:04 AM
trinitree88 trinitree88 is offline
Senior Member
 
Join Date: Sep 2005
Location: Massachusetts
Posts: 2,309
Wink ecliptic

Quote:
Originally Posted by max8166 View Post
I know the moon circles the earth every 29.5 days, and that it has an eliptical orbit, but how can I find out where it will be? Does it follow the equator in its orbit? The sun has a solstice as the axis of the earth changes over a year but does the moon have a solstice too?
max. If you sat on the same rock every sunrise, moonrise....the sun, moon, and the planets follow nearly the same path across the sky. If it was exact, there'd be an eclipse every month. It's approximate, so it isn't a line, but a band in the sky.. This band is divided into 12 sections. At sunrise, the sun appears to rise while in a constellation, that's the zodiacal "sun sign". 12 of them cover the year...hence, the signs of the zodiac.
When teaching the night sky, I sit a kid in a chair, facing ~ South, and have them follow the sweep of a laser pointer across the wall...motion of the sun. Successive sweeps rise slightly from Dec.21-June 21...drop slightly from June 21-Dec.21
If you pay attention to the daily sweeps, you should find the moon ~there at night, and the planets, too. You can naked eye see Mercury, Venus, Mars, Jupiter, Saturn (Earth)....This is the simplified version. Pete
__________________
A third rate theory forbids
A second rate theory explains after the fact
A first rate theory predicts...A. Lomonosov
Reply With Quote
Old 17-August-2006, 11:10 AM
trinitree88
This message has been deleted by Tinaa. Reason: by poster request
  #3 (permalink)  
Old 17-August-2006, 11:17 AM
gwiz's Avatar
gwiz gwiz is offline
Senior Member
 
Join Date: Oct 2005
Location: Cornwall
Posts: 965
Default

Most astronomy magazines publish monthly charts of where things are, including the moon. No doubt there are websites that do the same - suggest you google a bit - the word "ephemeris" might help.
__________________
"The truth may be out there, but lies are inside your head" Terry Pratchett
Reply With Quote
  #4 (permalink)  
Old 17-August-2006, 11:23 AM
cjbirch's Avatar
cjbirch cjbirch is offline
Member
 
Join Date: Dec 2005
Location: University of Hull
Posts: 68
Default

This website should help you find what your looking for!
http://www.fourmilab.ch/yoursky/
Reply With Quote
  #5 (permalink)  
Old 17-August-2006, 12:21 PM
grant hutchison grant hutchison is online now
Senior Member
 
Join Date: Jul 2005
Posts: 5,221
Default

The moon's orbit is inclined by about 5 degrees relative to the ecliptic plane. (The ecliptic plane follows the zodiacal band in the sky that trinitree88 described above.) The orbit twists around slowly in the ecliptic plane, maintaining a more or less constant tilt.
Within its orbital plane, the moon moves closer to the Earth (perigee) and farther from the Earth (apogee) at either end of its orbital ellipse. These points also migrate continuously around the orbital plane.
So its position in the sky is difficult to predict without some maths, and impossible to predict accurately without a lot of maths.
Websites or astronomy software are by far the easiest ways to find the moon's position.

Grant Hutchison
Reply With Quote
  #6 (permalink)  
Old 17-August-2006, 12:42 PM
max8166's Avatar
max8166 max8166 is offline
Senior Member
 
Join Date: Oct 2005
Location: Southampton, England
Posts: 227
Default

Oh this is good, this is just what I was looking for thanks
http://www.fourmilab.ch/earthview/moon_ap_per.html
Reply With Quote
  #7 (permalink)  
Old 17-August-2006, 02:36 PM
Blue Fire's Avatar
Blue Fire Blue Fire is offline
Senior Member
 
Join Date: Apr 2004
Location: Wyoming, NY
Posts: 445
Default 13 Constellations in Zodiac

From: http://www.astro.wisc.edu/~dolan/con...ra/Zodiac.html
Quote:
The Zodiac is the ring of constellations that the Sun seems to pass through each year as the Earth orbits around it. Contrary to popular belief, there are actually 13 zodiacal constellations, if you pay attention to the way astronomers define them. In addition to
Capricornus, Aquarius, Pisces, Aries, Taurus, Gemini, Cancer, Leo, Virgo, Libra, Scorpius, and Sagittarius,
the Sun also passes through
Ophiuchus
.
The bold is mine. Just thought I'd put my 2 cents in for the sake of being contrary.
__________________
How many times have you been about to grasp the truth when somebody else suddenly yanked it out of your reach?
Reply With Quote
  #8 (permalink)  
Old 17-August-2006, 02:57 PM
grant hutchison grant hutchison is online now
Senior Member
 
Join Date: Jul 2005
Posts: 5,221
Default

Quote:
Originally Posted by Blue Fire View Post
Quote:
Contrary to popular belief, there are actually 13 zodiacal constellations, if you pay attention to the way astronomers define them.
The twelve astrological "houses" familiar from newspaper horoscopes span 30 degrees each, so violate all the zodiacal constellation boundaries. Two of the houses (Scorpio and Capricorn) don't even have the same names as their parent constellations. The houses have also shifted relative to the background stars in the last few millennia, so that the astrological house of Ares is sitting in the constellation Pisces, and so on around the sky.

Grant Hutchison
Reply With Quote
  #9 (permalink)  
Old 17-August-2006, 10:27 PM
hhEb09'1's Avatar
hhEb09'1 hhEb09'1 is offline
Senior Member
 
Join Date: Apr 2005
Location: NC USA
Posts: 7,976
Default

Quote:
Originally Posted by max8166 View Post
I know the moon circles the earth every 29.5 days,
It actually circles the earth in a little over 27 days--so that it goes through the cycle of constellations in those 27 days.

Quote:
Originally Posted by trinitree88 View Post
This band is divided into 12 sections. At sunrise, the sun appears to rise while in a constellation, that's the zodiacal "sun sign". 12 of them cover the year...hence, the signs of the zodiac.
As grant hutchison mentions, astronomers use a different definition of the constellations than the astrologers do, but even then, the signs have shifted more than a whole sign because of precession so that the sun does appear in the current sun sign.
Quote:
When teaching the night sky, I sit a kid in a chair, facing ~ South, and have them follow the sweep of a laser pointer across the wall...motion of the sun. Successive sweeps rise slightly from Dec.21-June 21...drop slightly from June 21-Dec.21
If you pay attention to the daily sweeps, you should find the moon ~there at night, and the planets, too.
The difference in the height of the sun will vary as much as 47 degrees from early summer to early winter, but when the ecliptic is high in the day, it is low at night, so the height of the sun at local noon on the first day of summer can be 47 degrees higher than the height the moon or planets attain that night.
Reply With Quote
  #10 (permalink)  
Old 18-August-2006, 08:50 AM
max8166's Avatar
max8166 max8166 is offline
Senior Member
 
Join Date: Oct 2005
Location: Southampton, England
Posts: 227
Default

Quote:
Originally Posted by hhEb09'1 View Post
It actually circles the earth in a little over 27 days--so that it goes through the cycle of constellations in those 27 days.
Yes this is confusing me. On one hand we have:
Revolution period(Sidereal period)=27.32166155 days (27 d 7 h 43.2 min)
and on the other:
Synodic period = 29.530 588 days (29 d 12 h 44.0 min)

Any explaination would be gratefully received
Reply With Quote
  #11 (permalink)  
Old 18-August-2006, 09:25 AM
hhEb09'1's Avatar
hhEb09'1 hhEb09'1 is offline
Senior Member
 
Join Date: Apr 2005
Location: NC USA
Posts: 7,976
Default

Quote:
Originally Posted by max8166 View Post
Yes this is confusing me. On one hand we have:
Revolution period(Sidereal period)=27.32166155 days (27 d 7 h 43.2 min)
and on the other:
Synodic period = 29.530 588 days (29 d 12 h 44.0 min)

Any explaination would be gratefully received
The 29.5 days is the time between full moons, more or less. Since the earth and moon are revolving about the sun, the moon takes a couple more days to "catch up" to the point where it can be full again.

Similarly, the earth rotates in 23h 56m--it takes an additional 4 minutes to "catch up". If you add up those four minutes per day, over the entire year, you find that there is an additional day/rotation that is "lost" because of the revolution about the sun. Those extra couple days in the case of the moon add up to one full "lost" revolution.
Reply With Quote
  #12 (permalink)  
Old 18-August-2006, 10:07 AM
max8166's Avatar
max8166 max8166 is offline
Senior Member
 
Join Date: Oct 2005
Location: Southampton, England
Posts: 227
Default

So to position the moon in the longitudinal sense, in other words ignoring the latitude. Can I say that for every earth day (24 hours) the moon moves about 13.179 degrees ** in the sky? (just in the longitude plane)

** 360/27.32166155
Reply With Quote
  #13 (permalink)  
Old 18-August-2006, 10:58 AM
grant hutchison grant hutchison is online now
Senior Member
 
Join Date: Jul 2005
Posts: 5,221
Default

Quote:
Originally Posted by max8166 View Post
So to position the moon in the longitudinal sense, in other words ignoring the latitude. Can I say that for every earth day (24 hours) the moon moves about 13.179 degrees ** in the sky? (just in the longitude plane)
Afraid not.
1) Because the moon has an elliptical orbit, it moves alternately faster and slower across the sky.
2) When the moon is far from the celestial equator, it will cross more lines of celestial longitude for a given angular movement than it does when it's near the equator: the lines of longitude are closer together (as they converge towards the pole), and the moon is moving more nearly orthogonal to them.

Grant Hutchison
Reply With Quote
  #14 (permalink)  
Old 18-August-2006, 03:19 PM
max8166's Avatar
max8166 max8166 is offline
Senior Member
 
Join Date: Oct 2005
Location: Southampton, England
Posts: 227
Default

13.179 degrees, I meant just as an approximation, how many degrees would I be out by in the worst case? I was only trying to approximate. Also as the moon crosses the Ecliptic twice an orbit or is it twice a month, can you approximate the Latitude by making it equal to the latitude of the sun (plus or minus 5 degrees)
Reply With Quote
  #15 (permalink)  
Old 18-August-2006, 04:31 PM
grant hutchison grant hutchison is online now
Senior Member
 
Join Date: Jul 2005
Posts: 5,221
Default

Quote:
Originally Posted by max8166 View Post
13.179 degrees, I meant just as an approximation, how many degrees would I be out by in the worst case? I was only trying to approximate.
Approximate to a thousandth of a degree? .
I don't know the size of the error, and of course the calculations to determine that are almost as complicated as the calculations to get an exact position for the moon. But I'd guess on the order of a few degrees.

Quote:
Originally Posted by max8166 View Post
Also as the moon crosses the Ecliptic twice an orbit or is it twice a month, can you approximate the Latitude by making it equal to the latitude of the sun (plus or minus 5 degrees)
Again, afraid not. While the new moon will have the same approximate latitude as the sun, the full moon will have approximately the opposite latitude: south of the equator if the sun is north, north of the equator if the sun is south. Other phases will have intermediate latitudes.

Grant Hutchison
Reply With Quote
  #16 (permalink)  
Old 18-August-2006, 11:51 PM
Lord Jubjub's Avatar
Lord Jubjub Lord Jubjub is offline
Senior Member
 
Join Date: Jan 2005
Location: Land of Storm and Chaos
Posts: 1,689
Default

The moon is October and November is very low in the northern sky. So low that from Europe or Canada, it never completely achieves whiteness. The full moon at its height is still somewhat orange.

Or so I've heard. I've never had the chance to see the Hunter or Harvest Moon from that far north.
__________________
Keeper of the Jabberwock
Reply With Quote
  #17 (permalink)  
Old 19-August-2006, 01:10 AM
hhEb09'1's Avatar
hhEb09'1 hhEb09'1 is offline
Senior Member
 
Join Date: Apr 2005
Location: NC USA
Posts: 7,976
Default

Quote:
Originally Posted by Lord Jubjub View Post
The moon is October and November is very low in the northern sky. So low that from Europe or Canada, it never completely achieves whiteness. The full moon at its height is still somewhat orange.

Or so I've heard. I've never had the chance to see the Hunter or Harvest Moon from that far north.
Not sure what you mean here. The moon tends to be higher then.

My astronomy software says that on Nov. 5, 2006, at 23h UT, from Paris, the moon will be at a height of 57 degrees.
Reply With Quote
  #18 (permalink)  
Old 19-August-2006, 09:32 AM
max8166's Avatar
max8166 max8166 is offline
Senior Member
 
Join Date: Oct 2005
Location: Southampton, England
Posts: 227
Default

Taking a step back and looking at it another way, can I locate the moon if I know where the Ecliptic Plane is and then locate the moon on this plane preceding the sun by an approx cumulative 13.178 degrees per day, with a 5 degree oscilation about the ecliptic (with an oscilation period of half a rotation)?
Reply With Quote
  #19 (permalink)  
Old 19-August-2006, 01:18 PM
hhEb09'1's Avatar
hhEb09'1 hhEb09'1 is offline
Senior Member
 
Join Date: Apr 2005
Location: NC USA
Posts: 7,976
Default

Quote:
Originally Posted by max8166 View Post
Taking a step back and looking at it another way, can I locate the moon if I know where the Ecliptic Plane is and then locate the moon on this plane preceding the sun by an approx cumulative 13.178 degrees per day, with a 5 degree oscilation about the ecliptic (with an oscilation period of half a rotation)?
Um, yes, but I'm not sure what you mean by "preceding the sun". I think you mean, starting with a known position, the moon will advance through the approximate region of the ecliptic at roughly 13 degrees per day. It won't be exact, but it'll get you in the ballpark, unless you try to use it for predictions over very long periods of time.
Reply With Quote
  #20 (permalink)  
Old 20-August-2006, 12:47 AM
Kaptain K's Avatar
Kaptain K Kaptain K is offline
Senior Member
 
Join Date: Oct 2001
Location: Elgin, Tx
Posts: 7,568
Default

Quote:
The moon is October and November is very low in the northern sky.
You've got it backward. In the winter, the full Moon is very high in the sky. Just the opposite of the Sun.
__________________