How To Predict the Times of Moonrise and Moonset

The most relevant factor in determining the times of moonrise and moonset is the phase of the moon.  Here is a first approximation based on moon phase (mean moon phase, corresponding to mean elongation of the moon, also the moonstick definition of moon phase).

 

    

moonrise

    

moonset

new moon new moon

 

06:00 AM

 

06:00 PM

young crescent moon young crescent

 

09:00 AM

 

09:00 PM

first quarter moon first quarter

 

12:00 PM

 

12:00 AM

waxing gibbous moon waxing gibbous

 

03:00 PM

 

03:00 AM

full moon full moon

 

06:00 PM

 

06:00 AM

waning gibbous moon waning gibbous

 

09:00 PM

 

09:00 AM

last quarter moon last quarter

 

12:00 AM

 

12:00 PM

old crescent moon old crescent

 

03:00 AM

 

03:00 PM

new moon new moon

 

06:00 AM

 

06:00 PM

At this point you should be aware that the time you keep on your watch may not be the actual time where you are.  This can be for several reasons.  The biggest reason is probably "Daylight Saving Time".  In the summer, many countries set their clocks one hour ahead of what they would otherwise be set at.  Weather or not your country does this is up to you to find out.  Another reason your watch may differ from actual time is if you set it to a particular time zone.  Take me for example; I live at 85W longitude, but I set my watch to United States Eastern Standard Time, which is reckoned from 75W longitude.  This 10 difference means that I am actually 40 minutes behind the longitude from which my watch is set.  So when my watch says it is 12:40PM, it is 12:00PM locally.  (A 15 change in longitude changes local time by one hour.)

The times in the above table indicate actual time, so you will need to determine the difference between your watch time and the actual time.  Let me give you an example.  There is a person that lives near Chicago, Illinois at 88W longitude.  He (like most other people in that area) sets his watch to United States Central Time, which is reckoned from 90W longitude (in the winter anyway).  So he sets his watch 2 behind his local time.  (Behind means to the west, of course, because the Earth turns to the east.)  As stated earlier, a 2 difference in longitude corresponds to an 8 minute difference in local time.  So if moonrise is determined to be at 6:29PM local time; his watch will read 6:21PM when the moon rises.  (As we said earlier, he sets his watch 8 minutes behind local time.)  If it were summertime, he (like most of the other people in that area) would have his watch set an additional one hour ahead, thus his watch would read 7:21PM when the moon rises. 

Now that that is out of the way, we can get back to the actual predicting.  Step one, determine the current moon phase precisely.  Step two, make a first approximation of the times of moonrise and moonset from the above table.  (You must, of course, interpolate where necessary.)  Step three, adjust these times for the particular way that you set your watch.  You now have the times of moonrise and moonset within about an hour.  (If you are near the equator, you probably have it better than an hour.  If you are near the poles, you probably have it a lot worse than one hour.)

To get better, we must incorporate the season and latitude of observation into our prediction.  To do this, we will first use the season (mean season, corresponding to the mean ecliptic longitude of the sun) together with the moon phase to determine the mean location angle of the moon (corresponds to the mean zodiacal sign of the moon).

   

winter
solstice

 

·

 

spring
equinox

 

·

 

summer
solstice

 

·

 

fall
equinox

 

·

 

winter
solstice

   

new moon

    

000

    

045

    

090

    

135

    

180

    

225

    

270

    

315

    

000

    

new moon

young crescent moon

 

045

 

090

 

135

 

180

 

225

 

270

 

315

 

000

 

045

 

young crescent moon

first quarter moon

 

090

 

135

 

180

 

225

 

270

 

315

 

000

 

045

 

090

 

first quarter moon

waxing gibbous moon

 

135

 

180

 

225

 

270

 

315

 

000

 

045

 

090

 

135

 

waxing gibbous moon

full moon

 

180

 

225

 

270

 

315

 

000

 

045

 

090

 

135

 

180

 

full moon

waning gibbous moon

 

225

 

270

 

315

 

000

 

045

 

090

 

135

 

180

 

225

 

waning gibbous moon

last quarter moon

 

270

 

315

 

000

 

045

 

090

 

135

 

180

 

225

 

270

 

last quarter moon

old crescent moon

 

315

 

000

 

045

 

090

 

135

 

180

 

225

 

270

 

315

 

old crescent moon

new moon

 

000

 

045

 

090

 

135

 

180

 

225

 

270

 

315

 

000

 

new moon

Now use the mean location angle of the moon together with the latitude of observation (your latitude) to determine the amount (h:mm) by which moonrise should be corrected.  (The word "up/down" indicates that the moon does not rise or set but is up/down continuously.)

 

    

000

    

045

    

090

    

135

    

180

    

225

    

270

    

315

    

000

    

 

90N

 

down

 

down

 

0:00

 

up

 

up

 

up

 

0:00

 

down

 

down

 

90N

80N

 

down

 

down

 

0:00

 

up

 

up

 

up

 

0:00

 

down

 

down

 

80N

70N

 

down

 

+3:44

 

0:00

 

–3:44

 

up

 

–3:25

 

0:00

 

+3:25

 

down

 

70N

60N

 

+3:15

 

+2:12

 

0:00

 

–2:12

 

–3:15

 

–1:52

 

0:00

 

+1:52

 

+3:15

 

60N

50N

 

+2:04

 

+1:32

 

0:00

 

–1:32

 

–2:04

 

–1:12

 

0:00

 

+1:12

 

+2:04

 

50N

40N

 

+1:25

 

+1:07

 

0:00

 

–1:07

 

–1:25

 

–0:47

 

0:00

 

+0:47

 

+1:25

 

40N

30N

 

+0:58

 

+0:49

 

0:00

 

–0:49

 

–0:58

 

–0:29

 

0:00

 

+0:29

 

+0:58

 

30N

20N

 

+0:36

 

+0:34

 

0:00

 

–0:34

 

–0:36

 

–0:15

 

0:00

 

+0:15

 

+0:36

 

20N

10N

 

+0:18

 

+0:22

 

0:00

 

–0:22

 

–0:18

 

–0:02

 

0:00

 

+0:02

 

+0:18

 

10N

00

 

0:00

 

+0:10

 

0:00

 

–0:10

 

0:00

 

+0:10

 

0:00

 

–0:10

 

0:00

 

00

10S

 

–0:18

 

–0:02

 

0:00

 

+0:02

 

+0:18

 

+0:22

 

0:00

 

–0:22

 

–0:18

 

10S

20S

 

–0:36

 

–0:15

 

0:00

 

+0:15

 

+0:36

 

+0:34

 

0:00

 

–0:34

 

–0:36

 

20S

30S

 

–0:58

 

–0:29

 

0:00

 

+0:29

 

+0:58

 

+0:49

 

0:00

 

–0:49

 

–0:58

 

30S

40S

 

–1:25

 

–0:47

 

0:00

 

+0:47

 

+1:25

 

+1:07

 

0:00

 

–1:07

 

–1:25

 

40S

50S

 

–2:04

 

–1:12

 

0:00

 

+1:12

 

+2:04

 

+1:32

 

0:00

 

–1:32

 

–2:04

 

50S

60S

 

–3:15

 

–1:52

 

0:00

 

+1:52

 

+3:15

 

+2:12

 

0:00

 

–2:12

 

–3:15

 

60S

70S

 

up

 

–3:25

 

0:00

 

+3:25

 

down

 

+3:44

 

0:00

 

–3:44

 

up

 

70S

80S

 

up

 

up

 

0:00

 

down

 

down

 

down

 

0:00

 

up

 

up

 

80S

90S

 

up

 

up

 

0:00

 

down

 

down

 

down

 

0:00

 

up

 

up

 

90S

 

    

000

    

045

    

090

    

135

    

180

    

225

    

270

    

315

    

000

    

 

To determine the correction for moonset, reverse the latitude of observation (swap north and south).  You now have the correct times for moonrise and moonset within about 30 minutes.  To do better, we will have to correct for the eccentricity of the moons orbit.

This page is part of the Moonstick Information Site.
copyright 2000 Sean Barton, all rights reserved

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