Many astronomers enjoy viewing or taking pictures of the crescent or full Moon sitting above an interesting landscape or foreground. Here are some examples of mine (copyright):
In the past it was not easy for me to plan for moments like these, especially when I had restricted access to nice vantage points, but that day is over! Before I had to use a planetarium program and step through each month, possibly each day to see if the Moon's altitude and azimuth were about right, and what the altitude of the Sun was. What if you had several different favorite locations, where the foreground monument or mountain was in a different azimuth range? That's a lot of time spent searching. What if you had dozens of locations? Now you simply enter the altitude and azimuth range for each place into a "photosite" file (once), set a constraint or two, click search, and just watch the dates, times, and the right viewing places scroll down your screen!
When you call up the Rise/Set Alt/Az Search through the Utilities menu
you will see a new window with choices lined up on tabs. Each one has a purpose to suit your photographic or visual requirements. From the menu, you can also choose "Evening" or "Morning" if you are interested in only one part of the day. I've separated crescent from non-crescent because of the solar altitude. For crescents, you need a twilight sky, the Sun being some 7 to 9 degrees below the horizon. For non-crescents (first or last quarter, gibbous or full), to avoid an overexposed disk, you need the local terrain to be illuminated by daylight, so the Sun needs to be above the horizon or just setting. Farther down, you will see how to create a "photosite" list, your observation points. Remember that due to different atmospheric conditions and local topography, that the times given may be off by a minute or two.
Retrieve the alt-az of the Moon and Sun from any time:
Put in the date and time of your observation or photo at upper left, then click on "Current Solar/Lunar Alt/Az Values" to use the numbers for future opportunities.
Elong is the elongation in degrees from the Sun to the Moon as viewed from your observation point. The geocentric value is typically less than a degree different.
Illum is the % illumination.
How to use non-crescent (first or last quarter, gibbous or full):
Choose the solar altitude (typically zero or greater), the number of months, and hit search. If you want to additionally constrain the Moon's altitude above a certain amount, you can do that here.
Whenever there is at least one site that matches criteria, there is a datetime header, listing the solar and lunar altitudes and azimuths. Underneath it is a list of all your "photosites" that would have a nice view. In the above example, I could get a view from home on the 21st, go to St George's Crescent on the 22nd, and watch from the 142 St North bridge on the 23rd.
You can of course copy and paste the text output into other programs by clicking and dragging to select and using the standard Ctrl-c to copy and Ctrl-v to paste.
How to use the crescent search
In this case, we're looking for nice twilight backgrounds, not the ultrathin crescents:
The default solar altitude is -7.5 degrees, giving a nice rich twilight color, hit search and there's the answer. In March I have a chance only from Strathearn site overlooking the legislature building, and in April, only over the Telus building. In March, the lunar azimuth is too far south for it to show up in the Telus view. The altitude will tell me where to expect the Moon in the picture.
Simple Rise/Set table, choose Moonrise/set Azimuth search
Here you see a classic list of events for each calendar day. Note on the 31st there is no moonrise, because it occurs after midnight, early the next day.
If you're into moonrises or sets to watch for cool atmospheric effects, like in this image:
uncheck the "Simple Rise/Set" box, and the utility will filter out most of the events, leaving only the ones that you can see from your "photosite" list:
Specific Altitude/Azimuth Search:
What if you want to see when the almost full Moon shines down the long corridor at MIT, or lines up with stones in a Medicine Wheel? When does a Moon of any phase at anytime of day cross above the Tour Eiffel as seen from the Arc de Triomphe? As long as you know the altitude and azimuth, you can search for it! Add a constraint on the altitude of the Sun in order to specify the rough time of day/night/twilight. The default is no constraint. It may be important to you what the phase of the Moon is, whether thin or almost full. 100 means full Moon. A + sign means waxing, and a - sign means waning (based on colongitude so this is approximate). And of course you can specify how tight your requirements are by controling the size of the circle. A 1 degree circle is going to be tough to hit and will give you few dates, but a 10 degree wide circle allows a greater chance of the Moon passing through.
Caveat: the accuracy diminishes as you search centuries away from current time. At a minimum deltaT will be different, but the equations used in Lunar Calculator were not intended to be used for historical times.
Creating a photosite list:
Click on the tab that reads "PhotoSite List" to see the list that comes with Lunar Calculator. Do NOT remove the first five lines! They are there to guide you, and the program ignores the first 5 lines in this file. Use spaces, not tabs to line up the columns. Just type over or delete the 8 sites that I use, and hit save. It may take a while to discover the ranges for each site you are interested in. The smaller the ranges, the less often the Moon will be placed just right! A standard 50mm lens gives a field 40 degrees azimuth x 27 degrees altitude in landscape orientation. A 135mm lens gives 15 degrees x 10 degrees. At 1/2 degree, the Moon is disappointingly small with a 50mm!
What if my other sites are not in the vicinity of my location?
Ideally, the rise/set times, altitudes and azimuths would be calculated specifically for each site. A change in latitude can have a significant effect. For example, in the far north, a winter full Moon never sets. However, as long as your other sites are within an hour's drive or so, the times given in the list will only be a few minutes difference and the alt/az within a degree or two. If another site is different by 5 degrees latitude or longitude, go to the settings menu, create another location and run the utility especially for it.
Surprises
Because the orbit of the Moon gradually changes during the 18 year Saros cycle, you may be surprised that what was a perfect alignment last year is not possible this year. The twilight crescent shot above, I took the first spring after arriving in Edmonton, and 13 years later I still have not been able to equal it, partly due to bad luck with cloudy weather, but mostly because it is either too high, already set, or too far one side or the other! If I move location, then the legislature is blocked by other buildings.
Good luck on your adventures!
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