Can any of you engineer or scientific types (who seem to be the majority of the membership here) explain in layman's terms how to figure out where the sun is going to be on a particular date at a particular time at a particular location?
Let's say, for example, that I want to go to False Kiva and I want to shoot it on one of the days when the entire stone circle is in the sun. Or maybe I want to shoot a particular sandstone feature without the shadow of something else on it. How do I determine the date and time when that will occur? It's OK if I have to do a scouting trip and stand in the spot and take some kind of measurements to plug into an equation later.
Any help would be appreciated. Just keep in mind that my undergrad degree is in literature and post grad is law - and there is no math in either. Big words I understand; big numbers lose me fast!
Posted by Kalin Wilson on August 14, 2007 at 11:28 PM
CAZ,
First, Here is a tool that I've used several times before: Sun/Moon Calculator
You may have seen it before. It's been pretty accurate for me. I use google earth, or topo software to pick the lat/long of interest.
Also, my new GPS unit, the Delorme Earthmate, has a sunrise/sunset feature, so I use that now. I'm sure other units have similar capabilities.
But your questions is a little beyond sunrise/sunset times and locations. For info like you're asking, you would definately need to know the terrain features around your location to predict the effects of masking/shadows as well as the transit arc of the sun for a given date/season. Calculators like the above or an astronomy program can give you the arc or elevation angle of the sun. Using that and google earth, I bet you could pre-visualize pretty well.
Of course, local knowledge is usually king. When Rich and I went through Monument Valley, our guide told us the two dates to come back for the mitten's shadow alignment.
Good luck!
Posted by Kalin Wilson on August 14, 2007 at 11:34 PM
About half-way down you will find a link titled “Altitude and Azimuth of the Sun or Moon During One Day”
This page allows you to enter some data - date, location or coordinates - and it will give you a table of data where Sun (or Moon) will be located at any given time.
Plug in some numbers and check out the results. Then, take a look at the bottom of this page under “Notes on the Data” for an explanation. Hopefully, after a couple of tries, the whole thing should become fairly self-explanatory! (if not just ask some questions and some of us technical types will be happy to explain further)
Unfortunately, if you want to find out if a certain geographical feature is in light / shadow, you need to know its location and which way it is facing. This can be done by scouting and taking compass readings, or looking at a topo map. Keep in mind that certain features (mountains, canyons, False Kiva) might be blocked from sunlight by other objects in the landscape.
I have found that the scientific data may get you close, but you are going to gather the best data by actually visiting a spot and observing the light at various times of the year.
Posted by Jody Grigg on August 14, 2007 at 11:43 PM
I second Rene's comments.
Posted by Bob Falcone on August 15, 2007 at 12:55 AM
If you have a Palm based PDA a program called RiseSet will allow you to determine the setting and rising location/time of both the sun and moon. Works well.
Posted by Les Barstow on August 15, 2007 at 2:34 AM
My Garmin eTrex GPS has a Sun/Moon accessory that shows a crude graphic approximation of the compass locations for sunrise and sunset; it can be set to display a specific time/date or played through a timeframe. It also displays sun and moon rise and set times, but doesn't display altitude/azimuth.
There's nothing quite like being there - or getting a report from someone who's been there - Rene's right.
Posted by John Mumaw on August 15, 2007 at 7:34 AM
CAZ,
I use Rene's link all of the time to determine the location of the full moonrise.
I also used it to figure out when the MV event occurs in the Spring by adding six months to Sept. 13, then hunting through several days to find an exact match near sunset. I used Kayenta, AZ as my location. Anyplace close is good enough
Note that the standard compass bearing (NS 0º-90º EW) is given in azimuth (0º-360º) at this site. It also doesn't use Daylight Savings Time in its time/bearing calcs.
As noted, sun angles will be a bit more difficult. Knowing that most Anasazi ruins are in full sun during the Winter middays helps. For accuracy, you would need to use a clinometer (http://www.forestry-suppliers.com/product_pages/View_Catalog_Page.asp?mi=7086) to measure vertical azimuths, along with a compass.
As stated by others...the navy site is great for this info. Also, if you really want handy access to this information and you're out in the middle of no where...a GPS with sunrise and moonrise is also fantastic because it changes the time data no matter where you are. I used one on a road trip last year and it was very handy.
Cynthia Spence
www.geolightphoto.com
Posted by Phillip Noll on August 15, 2007 at 4:05 PM
Don't forget to factor in Daylight Savings time! Sounds obvious but I used the Navy charts once for moonrise and was an hour late. D'oh!
Posted by Mark Stahlke on August 15, 2007 at 5:58 PM
I like to use the sun/moon calculator in Kalin's link but I take the information with a grain of salt. One of the difficulties we Coloradoans face with tools like this is that they typically assume a flat, level horizon. Get up into the mountains and the horizon could be elevated 30 degrees or even more. That changes everything.
Posted by Les Barstow on August 15, 2007 at 6:34 PM
What Mark just said. However, if you've been to the location, you can pretty much figure based on degrees of elevation on the horizon just when sunrise will really be.
Also, sunrise is still sunrise, even if there's an obstacle in the way - the clouds will still light up at the listed sunrise time along with any unobstructed peaks, etc.; conversely, long shadows will provide definition long after sunrise if you're on a down-sloping hillside away from the Sun. In short, any tool you use is going to give you at best an approximation (until Google Earth can do 3D rendering with Sun-position-based lighting...).
Posted by Paul Wegemann on August 19, 2007 at 9:55 AM
I use a great little software package called Heavenly Opportunity.
http://weba.viawest.net/~fcs/ho/
OK, so this was a long time in coming but - Thank you to everyone who responded to my query! I really appreciate everyone's input.
I will certainly be sticking with the sites that provide the more basic information and calculations. However, while digging through some of the links Kalin provided, I found a page that claims that it is possible to determine when the sun will be blocked by topographical features - at least for those of the more technically-minded of you all.
For those who are so inclined, you may want to play around with the information provided on this page.
Discussion
13 repliesLet's say, for example, that I want to go to False Kiva and I want to shoot it on one of the days when the entire stone circle is in the sun. Or maybe I want to shoot a particular sandstone feature without the shadow of something else on it. How do I determine the date and time when that will occur? It's OK if I have to do a scouting trip and stand in the spot and take some kind of measurements to plug into an equation later.
Any help would be appreciated. Just keep in mind that my undergrad degree is in literature and post grad is law - and there is no math in either.
First, Here is a tool that I've used several times before:
Sun/Moon Calculator
You may have seen it before. It's been pretty accurate for me. I use google earth, or topo software to pick the lat/long of interest.
Also, my new GPS unit, the Delorme Earthmate, has a sunrise/sunset feature, so I use that now. I'm sure other units have similar capabilities.
But your questions is a little beyond sunrise/sunset times and locations. For info like you're asking, you would definately need to know the terrain features around your location to predict the effects of masking/shadows as well as the transit arc of the sun for a given date/season. Calculators like the above or an astronomy program can give you the arc or elevation angle of the sun. Using that and google earth, I bet you could pre-visualize pretty well.
Of course, local knowledge is usually king. When Rich and I went through Monument Valley, our guide told us the two dates to come back for the mitten's shadow alignment.
Good luck!
http://www.gearthhacks.com/forums/showthread.php?t=4086
http://bbs.keyhole.com/ubb/showflat.php/Cat/0/Number/55523/an/0/page/7
http://freegeographytools.com/2007/sun-position-during-the-day-for-any-location
Later!
http://aa.usno.navy.mil/data/
About half-way down you will find a link titled “Altitude and Azimuth of the Sun or Moon During One Day”
This page allows you to enter some data - date, location or coordinates - and it will give you a table of data where Sun (or Moon) will be located at any given time.
Plug in some numbers and check out the results. Then, take a look at the bottom of this page under “Notes on the Data” for an explanation. Hopefully, after a couple of tries, the whole thing should become fairly self-explanatory! (if not just ask some questions and some of us technical types will be happy to explain further)
Unfortunately, if you want to find out if a certain geographical feature is in light / shadow, you need to know its location and which way it is facing. This can be done by scouting and taking compass readings, or looking at a topo map. Keep in mind that certain features (mountains, canyons, False Kiva) might be blocked from sunlight by other objects in the landscape.
I have found that the scientific data may get you close, but you are going to gather the best data by actually visiting a spot and observing the light at various times of the year.
There's nothing quite like being there - or getting a report from someone who's been there - Rene's right.
I use Rene's link all of the time to determine the location of the full moonrise.
I also used it to figure out when the MV event occurs in the Spring by adding six months to Sept. 13, then hunting through several days to find an exact match near sunset. I used Kayenta, AZ as my location. Anyplace close is good enough
Note that the standard compass bearing (NS 0º-90º EW) is given in azimuth (0º-360º) at this site. It also doesn't use Daylight Savings Time in its time/bearing calcs.
As noted, sun angles will be a bit more difficult. Knowing that most Anasazi ruins are in full sun during the Winter middays helps. For accuracy, you would need to use a clinometer (http://www.forestry-suppliers.com/product_pages/View_Catalog_Page.asp?mi=7086) to measure vertical azimuths, along with a compass.
Cynthia Spence
www.geolightphoto.com
Also, sunrise is still sunrise, even if there's an obstacle in the way - the clouds will still light up at the listed sunrise time along with any unobstructed peaks, etc.; conversely, long shadows will provide definition long after sunrise if you're on a down-sloping hillside away from the Sun. In short, any tool you use is going to give you at best an approximation (until Google Earth can do 3D rendering with Sun-position-based lighting...).
http://weba.viawest.net/~fcs/ho/
It might be worth a look.
I will certainly be sticking with the sites that provide the more basic information and calculations. However, while digging through some of the links Kalin provided, I found a page that claims that it is possible to determine when the sun will be blocked by topographical features - at least for those of the more technically-minded of you all.
For those who are so inclined, you may want to play around with the information provided on this page.
Thanks all!