moonset variations

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dpdrake

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Having just moved to a location where I can see most moonsets, I have realized that where the moon sets on the horizon varies widely! It is almost as wide a range during a month as the sun is during the year. I can't tell if this is a regular pattern every month or only some months. I wonder if it is caused by the 5 degree offset of the moon's orbit? It seems to be a tilting of the elliptical rather than the orbit being higher in the sky. This is mostly observed in the summer in Bellingham, WA.
 
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MeteorWayne

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Welcome to Space.com!<br />I'm working on some real data for your location.<br />Briefly, you have 3 factors at work here.<br />One is the seasonal 23 1/2 degree tilt. (47 degrees over a year)<br />The other is the +/- 5 degree moon offset to the earth's 23 1/2 degree tilt.<br /><br />Finally, there is the angle of the ecliptic and how much of it is above the horizon.<br /><br />I picked a location in Washington, haven't had a chance to find Billingham. When I have more time later <img src="/images/icons/smile.gif" /><br /><br />I suspect you have underestimated the annual sunrise and sunset angles.<br /><br />Here's some data. Again, when I have time, I'll give more accurate numbers. First, the sun.<br /><br />Sunrise.... Sunset (I feel a song coming on)<br />---------<br />Time (not accounting for "savings time")<br />Azimuth.<br /><br />Winter Solstice <br />07:55 125 (ESE).......1620...235 (SW)<br />Summer Solstice<br />04:11 055 (ENE).......2011...305 (NW)<br /><br />Maximum Elevation Winter 19 degrees, Summer 66 degrees.<br /><br />So, during the year, the sunrise and sunset locations shift ~70 degrees, much more than the interseasonal shift in maximum elevation, since when the sun is higher, more of the path is above the horizon.<br /><br />The moonrise and set can be 5 degrees more in either direction....but the "more path above the horizon" also applies. So, napkin calculations here, in a month the moonrise and set positions can vary maybe 20 degrees, if I'm right. <br />The sun location varies by 70 degrees or more.<br /><br />If you don't mind, can I ask a few questions? Feel free not to answer if you wish, but I'm trying to understand your perception.<br /><br />How long have you lived there? Less than a year or many years?<br />Is it a flat area, or is it more mountainous where some directions have a higher horizon?<br />Where did you live before (just the state)<br /><br />Finally, how long ago did you notice this? I find it an interesting insight into our perceptions on the first imp <div class="Discussion_UserSignature"> <p><font color="#000080"><em><font color="#000000">But the Krell forgot one thing John. Monsters. Monsters from the Id.</font></em> </font></p><p><font color="#000080">I really, really, really, really miss the "first unread post" function</font><font color="#000080"> </font></p> </div>
 
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dpdrake

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wow! that was a wonderful reply! I wonder what you'll come up with? <br />Bellingham is just below the Canadian Border, so approx 45 degrees N. I'm observing over the water, mostly, at a height of about 300 ft. There is a higher point on the westernmost edge of my visual. (I'm looking northwest).<br />I admit I was exaggerating the moonset range in relation to the sun's, but the range is at least two thirds the range of the sun's, and happens within a month. I would say I have observed about 25 moonsets during the course of my stay here, since april 2006, with maybe 5 days in a row on occasion. I have some pictures that could demonstrate the range and the extent of the moonsets. <br />I've lived here for 30 years and took a long time to get used to the sun cycles, but am now fairly comfortable with them, especially having been to Alaska to compare. I moved up to this hill recently, and am amazed at the variations I've observed in Moon cycles. The simple idea that the moon eliptic lowers as the sun's gets higher and vice versa in the winter gets complicated in the summer here. The moon is much higher overhead now, and seems more consistant, but the weather is bad, so no moonsets to observe.<br />Thanks so much for your help and ideas!<br />
 
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nexium

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My guess is meteorwayne gave a good (but not perfect) answer. If 19 degrees is the correct December 22 maximum altitude for Washington State, then the Moon should not rise at all, 22 degrees farther North in December and early January. Was that your observation when you were in Alaska?
 
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pizzaguy

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Well, I am no astronomer, but I have eyes. <br /><br />I am suprised no one else has mentioned this, but the moon's elevation above the horizon varies a LOT in a month. <br /><br />For example: right now, we are at full moon. So, about midnight, go out and take a look at the moon - at that time, it'll be about directly south of you. Notice it's elevation above the horizon. <br /><br />Now, go out once a day (and you'll have to observe the moon about 30-45 minutes later each day) and observe the moon (in it's changing phase, but that's not the point) as it climbs to that same point (about due south). After a week or so, it'll be due south of you as a last-quarter moon in about that same position BUT IT'LL BE EITHER A BIG HIHGER OR LOWER IN THE SKY - still about due south, but not at the same distance from THE SOUTHERN HORIZON!<br /><br />I have observed this for 30 years or so, but it is VERY MUCH MORE OBVIOUS here in Georgia than in MIchigan. I have seen full moons almost directly overhead, and I"v seen them show up low in the sky in the trees. <br /><br />-----<br /><br />Here's another way to see what I mean. Go to your calendar, and IF the full moons are not already on it, get an almanac and label your calendar for each and every full moon for the next year.<br /><br />NOW, EVERY MONTH on the full moon, go outside at the same time EACH MONTH on the day of the full moon. 12 midnight is a good time. Notice the moon and try to measure it's distance to the horizon DIRECTLY SOUTH OF YOU. <br /><br />NOW, do the same the NEXT year, and you'll find that this is NOT just caused by the seasonal thing (the earth's tilt on it's axis) as the HIGHEST point above due south that the moon reaches won't be the same each year. In fact, the moon hits a low in the sky and a high in the sky several times a year.<br /><br />You will see something interesting: the moon varies between very low in the sky and quite high in the sky over the course of a month. <br /><br />W <div class="Discussion_UserSignature"> <font size="1"><em>Note to Dr. Henry:  The testosterone shots are working!</em></font> </div>
 
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rfoshaug

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A similar discussion occured here just a few weeks ago in this thread.<br /><br />I'll quote my post from that thread, which hopefully will shed some moonlight on the issue:<br /><br /><blockquote><font class="small">In reply to:</font><hr /><p><br />I live at 69° North, and this is how it looks from here:<br /><br />Each month there is a period when the moon is constantly above the horizon for several days. Then it gets lower in the sky, and there's a period when it rises and sets each day. Then there's a period when it is below the horizon and cannot be seen for several days until it starts going higher each night until it is constantly above the horizon again. This entire cycle takes about a month.<br /><br />The lunar phase at which these events occur vary with the season. This has a reason: At full moon, the sun and moon are in exact opposite parts of the sky (that's why we get to see the fully illuminated side of the moon). So at full moon, the moon is where (relative to the background stars) the sun will be in exactly 6 months, while at dark moon the moon is where the sun is at that time.<br /><br /><br />This means that at full moon in winter, the moon is going as high in the sky as the sun is in the summer, and at 69ºN this means that the full moons around christmas never sets. In the early summer, however (end of June), the full moon cannot be seen as it is constantly below the horizon just like the sun will be 6 months later.<br /><br />This is how the moon behaves as seen from north of the arctic circle ("normal" means it both sets and rises every day):<br /><br /><pre><br />Date | Dark moon | Waxing | Full moon | Waning<br />-------------|-------------|-------------|-------------|-------------<br />March 21 | Normal | Never sets | Normal | Never rises<br />June 21 | Neve</pre></p></blockquote> <div class="Discussion_UserSignature"> <p><font color="#ff9900">----------------------------------</font></p><p><font color="#ff9900">My minds have many opinions</font></p> </div>
 
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pizzaguy

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I never thought of the view you'd have so far north!<br />I thought the effect was more random - but I was wrong. I ran "MoonBrat" last night and it showed just what you described. <br /><br /><br /> <div class="Discussion_UserSignature"> <font size="1"><em>Note to Dr. Henry:  The testosterone shots are working!</em></font> </div>
 
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rfoshaug

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The downside of all this, is that it will now be a long time until next time I get to see Jupiter and Saturn again through my telescope, as they will be low in the sky or below the horizon for several years to come as they are moving into the part of the ecliptic that never rises above the horizon. <img src="/images/icons/frown.gif" /> <br /><br /><font color="orange"><br />BTW, Happy New Year, Pizzaguy! <img src="/images/icons/smile.gif" /><br /></font>/safety_wrapper> <div class="Discussion_UserSignature"> <p><font color="#ff9900">----------------------------------</font></p><p><font color="#ff9900">My minds have many opinions</font></p> </div>
 
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MeteorWayne

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Saturn is 45 degrees above the horizon at 3 AM in the morning for Oslo. 33 degrees above at midnight.<br /><br />You comment about it missing for years makes no sense to me.<br /><br />Where in Norway are you? Which of these is closest? (Please excuse spelling errors)<br />Bergen, Narvik, Stavager, Tromso, Trondheim, or Oslo <div class="Discussion_UserSignature"> <p><font color="#000080"><em><font color="#000000">But the Krell forgot one thing John. Monsters. Monsters from the Id.</font></em> </font></p><p><font color="#000080">I really, really, really, really miss the "first unread post" function</font><font color="#000080"> </font></p> </div>
 
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dpdrake

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Sorry I've been away a few days and it seemed like space.com was down!<br />anyway, Pizza makes some great observations, I think. It sounds like the moon's orbital path (eliptic?)changes a lot in all seasons. it also sounds irregular. <br />I was down in olympia, wa, the last two days, where my friend can watch moonrises. there was maybe a 5 degree difference (further north) on the horizon. pretty surprising. maybe a foot sweep at the end of your outstretched arm. <br />I am very interested if there is any pattern to this.<br />thanks for all the input!<br />
 
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dpdrake

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to nexium,<br /><br />on the contrary, I believe the moon reaches its highest point in the sky on Dec 22.
 
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dpdrake

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dear meteorwayne,<br /><br />well, I am chastized... you were right to suggest I go back and verify observations. I just looked at my pictures and you are right to say that the moonset varies around 20 degrees during the month. maybe less! I confused my images with some others I took at solstice. However, 20 degrees in a month is still a lot! Is this mostly the 5 degrees offset of the orbit? I am still digesting your first post, but any clarifications for amateurs are welcome, ie. the solstice numbers.. ?
 
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MeteorWayne

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Hey, I didn't mean to chastize you <img src="/images/icons/smile.gif" /><br />But I'm glad you went back and checked.<br />Yes 20 degrees is a lot in one month, but it makes sense. It's a combination of the 5 degree offset, and the fact that when it is higher in the sky (i.e. +5 degrees) you can actually see more of the path.<br /><br />I'll try and make a diagram later this afternoon, if time permits.<br /><br /> <div class="Discussion_UserSignature"> <p><font color="#000080"><em><font color="#000000">But the Krell forgot one thing John. Monsters. Monsters from the Id.</font></em> </font></p><p><font color="#000080">I really, really, really, really miss the "first unread post" function</font><font color="#000080"> </font></p> </div>
 
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rfoshaug

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<blockquote><font class="small">In reply to:</font><hr /><p>Saturn is 45 degrees above the horizon at 3 AM in the morning for Oslo. 33 degrees above at midnight.<br /><br />You comment about it missing for years makes no sense to me.<br /><br />Where in Norway are you? Which of these is closest? (Please excuse spelling errors)<br />Bergen, Narvik, Stavager, Tromso, Trondheim, or Oslo<p><hr /></p></p></blockquote><br /><br />Sorry, MeteorWayne, I was totally wrong about Saturn.<br /><br />Jupiter will now be lost for some time, but Saturn will still be around for a few more years. I actually had a very nice view of it about 20 or so degrees east of the Moon on Friday night. Tromso is the Norwegian city that is closest to where I live, btw.<br /><br />When Saturn goes missing in a few years, it will be gone for some years before it again appears above the horizon. But you are correct - I was wrong when I claimed that Saturn was already gone (have had a lot of cloudy weather here so far this autumn/winter and haven't had a chance to do much observing), so sorry about that. <img src="/images/icons/wink.gif" /> <div class="Discussion_UserSignature"> <p><font color="#ff9900">----------------------------------</font></p><p><font color="#ff9900">My minds have many opinions</font></p> </div>
 
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MeteorWayne

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Just didn't want you to miss it while still visible <img src="/images/icons/smile.gif" /> <div class="Discussion_UserSignature"> <p><font color="#000080"><em><font color="#000000">But the Krell forgot one thing John. Monsters. Monsters from the Id.</font></em> </font></p><p><font color="#000080">I really, really, really, really miss the "first unread post" function</font><font color="#000080"> </font></p> </div>
 
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