Category Archives: Trivia

Geometry and The Moon

Please do not run away. We are about to use adult language here. For example we will be using the word trigonometry. Still here? Good.  Here is a very pedestrian looking lunar eclipse photo taken with a 280mm lens*, cropped.

Near and Distant Neighbors

Very Ordinary Photo of the Lunar Eclipse with the planet Uranus in the lower left.

This past lunar eclipse several of us put our heads together to try to come up with a more creative photo than the one above. We had a trigonometry problem, however. On the West Coast the last moment of totality occurred at 4:24 AM PDT. We were brave enough to be out at any time of night – even if it meant extreme sleepiness in our day jobs but our problem was that the lowest the moon would be in the sky at the last bit of totality was 32.6 degrees above the horizon. We determined that angle using Stellarium, by the way. Unfortunately there is pretty much nowhere to go to get a nice large moon near an interesting object when the moon is almost 33 degrees high.

Wait: Why do we want the moon and the object to be similarly sized? Here is why… we want the moon to be noticeable like the Fantasy version below, not merely “present” like the real photo on the right. Even bigger would be better, right!?


Notice above right (Reality) and below how tiny the moon is compared to the building in the foreground?  Indeed, if you see a photo taken from anywhere on the West Coast where the eclipsed moon is significantly lower in the sky or larger than shown against foreground, you know it has been “photoshopped“.

Plan C: San Jose City Hall Eclipse Sequence

In short, it is nigh impossible to get the large moon effect with an altitude (angle) of 32 degrees here is why:

Calculating the Angles

Calculating the Angles

Just how far away do we need to be in order to get the moon the same size as an object of interest:

114.6 x object size

In other words, an object that is one foot tall, requires us to stand 114.6 feet away to make the 1/2 a degree angular size of the moon the same angular size as that 1 foot tall object.  The number “114.6” is from this calculation:

1 / TAN (0.5 degrees)

Yeah, that is trigonometry. Using still more trigonometry it is possible to calculate how high above the horizon a 9 inch tall object has to be so that it is “moon sized”.  We did that for you in the “Calculating the Angles” diagram above. Once you calculate the distance from the camera of 85.9, you can multiply that by the sine of the angle to calculate a height of about 46 feet! Here is the trigonometry:

Height = 85.9′ * SIN (32 deg)

You can go one step farther and calculate the distance from the object with ‘distance = 85.9 * COS(32 deg)’.

Of course after all that calculating you will still need to find a location, have contingency plans for weather and so on. At StarCircleAcademy we have built some tools and put together materials to help in all these endeavors.  We teach these things in our NP111 Catching the Moon Webinar.

The Road To The Temple

Below is where we ended up. This image is from our friend and co-conspirator Andy Morris.

Lunar Eclipse over Temple by Andy Morris of PhotoshopScaresMe

Four of us plotted and schemed to get an interesting shot. Above is Andy Morris’ result.  Click the image and you can read a great article about how he created the shot using Photoshop Skills at his site: In fact, it’s a great article which we strongly encourage you to read. You’ll learn how he composited the images together in Photoshop as layers.

The Long Conversation to Pick a Location

Andy has more details including how alcohol played a part in the process. Mostly I, Steven, was the wet blanket explaining why the geometry was all wrong.

  • The Stanford (Hoover) Tower looks like it is shrouded in trees from the needed angle
  • Bank of Italy (formerly BofA) in SJC doesn’t work
  • The main problem with the wind turbines is that the angle to the top of them is something around 12 degrees above the horizon which is 40 moon diameters below the eclipse.
  • Here is why the GG Bridge doesn’t work…
  • This seems to be the best solution I could find: the Coit Tower…
  • Darn. It would appear the coast is out. Forecast calls for Fog from SF to HMB
  • This might make an interesting foreground (see below)… Somebody want to check if they will mind us being on their property in the wee hours?

*Ok, we lied, it was actually a 70-200mm lens with a 1.4 TC on a full frame camera, but the net is the same: 280 effective mm focal length.

Where did you go and what did you get in your planning efforts?  Post a comment and link below… we’d love to see what you came up with!

Hunting Comets and other faint objects in not-dark skies

AirGlow Comet [5_070386]

It turns out the much hyped PanSTARRS C/2011L4 Comet is not living up to the hype. Unfortunately failure to meet the over exhuberant expectations  is common since predicting brightness and visibility of an object like a comet is a difficult science. In fact, it’s part science, part black art and part good guessing – mostly the latter.

The photo above was taken on March 12 when the moon and PanSTARRS nestled closely together. The close quarters made finding the comet much easier despite the bands of clouds passing by.  The strategy for finding the comet in that case was simple: use a telephoto lens, put the moon at the right edge of the photo and take different exposures periodically and at different settings (e.g. +2, 0, and -2 stops). Then hunt for smudges.

The IDEAL telephoto lens would be one that was a few angular degrees wider than the difference between the moon’s position and the comet’s position. How to determine the position of each is discussed in the last section below. Figuring out the angular view of your lens is easy using online tools like this one from Tawbaware, makers of Image Stacker (like that program!). If you know the field of view at your minimum and maximum zoom, you can use that information to your advantage.

Finding the Comet with a Nearby Moon

The point at the moon strategy made finding the comet easy because:

  1. There is no way you’d be able to see the comet if you were not able to find the much brighter moon nearby.
  2. On that one night, the comet and the moon were within 4 degrees of one another.  That’s quite close.

I know some people tried to find the comet using wide angle lenses. That strategy might work, but the comet is such a tiny thing and it’s visibility is so tenuous based on the atmosphere, light pollution, and sky brightness that you may only realize – as many did – that you captured the comet after carefully inspecting your photos at home.

Contrails and Comet Tails [B_050938]

The truth is you are unlikely to see PanSTARRS by eye or in your camera’s view finder unless your conditions are nearly ideal.  Hopefully ISON which is coming in December will be brighter and better.

Finding the Comet when the Moon is Farther Away

The following night, both the comet and the moon had moved relative to the sky. On March 13, the moon was 12.5 degrees above the comet and about 4 degrees farther west (again, how I knew this is coming in just a minute).  So one simple strategy for finding the comet would be to zoom your telephoto lens so that it has a field of view of about 14 to 15 degrees in the long direction which for me, is 80 millimeters focal length on a 1.6 crop factor camera.

On a tripod with the camera in portrait orientation adjust the view so that the the moon is in the upper left of the frame. Shoot bracketed shots. Check the lower right corner of each one for the tell-tale comet smudge.  Keep readjusting the view so the moon remains in the upper left for each shot. Zoom out a little bit too, in case your geometry is a little off. Eventually as it gets dark enough or the sky clear enough you should find it.

In fact the way I found the comet last night without using my camera but by using my telescope. The program Clinometer (on my iPhone) measures angles. I sighted the moon with my 8″ Dobsonian telescope and measured the angle along the telescope barrel using the inclinometer program. I then lowered the altitude (elevation angle) of the telescope by 12 degrees to match the altitude of the comet. Then I slowly rotated the telescope northward until I found the comet.  It wasn’t easy from my urban location, but it wasn’t impossible either.  By the time I was able to find the comet it was only about 6 degrees high in the sky – that’s way too low if you have trees, hills, and houses nearby to deal with.  In theory, this strategy would work with a telephoto lens or with binoculars, however, binoculars need to be steady and where I spied from last night had streetlights in the distance and the flare and glare from those streetlights made finding the faint comet nigh impossible.

What if there is no Moon to Find the Comet With?

Unfortunately starting on March 14th, the moon will be quite far from the comet, so the opposite strategy is required:  Use a landmark in a known direction as the starting point and look “upward” from the horizon.  In other words, zoom your telephoto lens so that the field of view covers the angle from the horizon to the comets altitude (angle) above the horizon.  Don’t forget that as the earth spins this angle changes every minute! Orient you camera in landscape mode and point it as close as you can to the correct direction (azimuth). Look along the top of the frame to see if you’ve captured the comet.


SpyGlass’s view shows the direction the camera is facing (Azimuth) and the elevation angle (Altitude)

But what direction should you point your lens or telescope? Use a compass application or actual compass. BEWARE however as the compass applications have lots of gotchas and are only accurate to about 5-10 degrees.  And if you aren’t sure how to use a real compass your local magnetic declination might bite you. Better would be a GPS with a built-in calibrate-able compass.  And perhaps even better still would be to use an application like TPE (which I discuss in my Catching the Moon Webinars) to calculate the correct azimuth from the location you plan to stand.  An application that might help a lot is “SpyGlass
however don’t forget that I found the directional accuracy of my iPhone and iPad to be pretty poor.  Being off by 5 degrees may mean looking in the wrong place.

How Do I Know the Altitude and Azimuth for the Comet?


Unfortunately, that’s a tough one.  I use the free program Stellarium. I then added the comet to the “Solar System Data Base” (search around on the web and you’ll find instructions). I selected my viewing location, dialed in the time, did a search for good ‘ol C/2011 L4 and let it tell me the azimuth and altitude.


Above I’ve dialed up the time and clicked the moon. The highlighted line shows me the azimuth (direction) and altitude (angle above the horizon) for the moon which at that time are 264 degrees or just a little south of west, and 30.5 degrees high.  Clicking on the comet shows 272 degrees – a tiny bit north of west and 9.5 degrees.  So now we know that the comet will be 8 degrees north and 21 degrees south of the moon – and that won’t change significantly for the rest of the night.

Since we also know the direction for the comet is about due west at this time, we can apply the telephoto-lens horizon trick I described earlier.

Another way you can find the azimuth and altitude is by checking my animation HERE – note that the animation is correct for San Francisco  (and most places nearby).  There is also a table of the azimuth and elevation in the text of the Flickr post.


By the way, one way to find the right spot on the horizon is to use the sunset location as a guide.


Now Open: The Store

So many of our students at our webinars and workshops as well as our website visitors ask us about our Notes, Instructional Videos and Photoshop additions that it was time to make it possible to deliver them.  So we created a digital store integrated with this blog.  In fact, we’ve only had the store open for two weeks and already we have a clear bestseller:

Advanced Stacker PLUS [14E] with Online Video and Notes
Includes the even EASIER to install Advanced Photoshop action set version 14E, an unlimited viewing online video on creating star trails, notes (PDF) on creating star trails and practice files. The video is 2 hours long. This action is power. You can create star trails, cloud timestacks and stack images with a minimum of effort and a maximum of control. You can create "comets", "midgets" streaks and much more. And you can create intermediate files along the way to put interesting motion effects into your timelapse. Compatible with Photoshop CS6 (standard or extended), CC, CC 2014-2018. While we have every reason to believe compatibility with CS3, CS4, CS5, and CS5.5 still works, we have no means to test these.
**NOTE: MAC Users with Yosemite or El Capitan, or Sierra and PS CC 2015 or later are reporting installation problems. We recommend you do NOT purchase this product until we have been able to resolve this issue. NOTE: We believe ASP DOES work properly with High Sierra and CS6 and CC 2018.
NOT Compatible with Photoshop Elements, or Lightroom. Please specify your primary OS and Photoshop version when ordering. You will receive links to both Mac and Windows installers.

Making It So

But making it so was not a straight line path from where we were to where we wanted to go. We toyed with a variety of things to create a store. Using PayPal buttons directly – simple and maddeningly painful at the same time, using ZenCart, and looking at a few others solutions.

Ultimately we wanted something relatively simple. Something that could handle a small, but growing array of products – all digital, and that would be relatively easy to integrate into the BLOG without breaking off limbs or snapping frazzled nerves. We settled on WP E-Store. It’s neither flawless nor as spectacularly simple to get working as we would want it to be, but it is well featured and well supported.

I should probably make a note that I, Steven, am capable of twiddling with HTML, circumspect of all CSS (because I’ve never found it to be pleasant to deal with), able to write JavaScript and PHP when needed – but prefer not to. If none of that makes sense to you, that might be fine unless you decide to embark on creating a store because I’ve already learned that I have needed all those skills in some form already.

We want a store secure against theft, hacks and intrusion, that is easy to use and easy to configure. We also want to offer discounts to people who attend our Webinars and Workshops as well as repeat customers. Using PayPal directly proved unmanageable. Our store also needs to manage the digital content that gets created on an almost daily basis. We had no expectation or illusion that we would sell prints or images through this store. In fact, Steven has a well featured means for selling hard goods through ZenFolio. Interestingly most Steven’s print sales occur in the United Kingdom – likely because they see Steven’s images in the Royal Observatory. ZenFolio is great for selling prints and mounted images – even iPhone cases!

WP eStore

What we like about WP eStore is that it does handle the key things we want: digital sales through PayPal (and credit cards), and secure encrypted links for digital goods and a nice simple interface for our clients and customers.

What WP eStore lacks, however are a number of things including a simple way to process refunds (always a painful thing through PayPal), more configurability of the display of products and the shopping cart and a few gotchas in the way you configure products. For example, with WP eStore you can specify a “thumbnail” image for a product – but by default the thumbnail will be clickable and go to the thumbnail image. That’s completely silly.

Of course since we purchased WP eStore we’ve also noticed a lot of other competitors, including WooCommerce which looks snazzy, but it appears you get nickeled and dimed to death to get all the pieces together.

Biggest Obstacle

The biggest impediment to our eStore is our theme.  Theme? Yes, the page layouts are controlled by a WordPress theme. Unfortunately the theme we like is not as customizable as we’d like. That spiffy graphic at the top, for example clutters up the store so we are planning to either switch themes or hack up the Twenty-Ten theme we are using.

What is Ahead?

One day we hope to also offer free and paid Webinar registration through the store. And perhaps even workshops, too. Please check out our store. Here is another resource of interest:

>Photography with Harold Davis obviously this is Harold’s spot and covers much more than night photography.

Oh, and if you would like to see if a Webinar will work for you and your set up, you can join a FREE webinar to kick the tires on March 12, 2013. We hope to see you there!

Untimely Battery Death: How to Avoid It.

As a night photographer I’m a proponent of the philosophy of “carry a big battery” and you’ll never miss that shot.  However I learned a hard lesson about my corral of batteries that I feel I must pass on before you too shriek in terror when you find your once reliable battery has met an untimely (and inconveniently timed) demise.

Lithium Batteries are Greatly Disturbed By Heat

This was the lesson I learned the hard way. I had a stable of five fully charged batteries ranging in size from 1800 milliamp hours all the way up to 8,000 milliamp hours. I kept them in a shaded part of my car through some summer days in the San Francisco Bay area.  And that was how I learned that Lithium + Fully Charged + Heat = premature death.  The two low capacity batteries previously allowed me two and a half hours worth of continuous night exposure. Now they each last about 12 and 15 minutes.  The three HUGE batteries that could easily power my camera all night long for continuous exposures now have about the same life in them as my regular 2000 mA hr batteries – that is, about 1/3 as long as they used to last.

I learned why my brutish batteries became so feeble at Battery University.  In a nutshell I discovered that storing batteries cool (less the 86 F) and at 40% charge is the most effective at prolonging their life.  What I do now is keep all of my batteries in a separate pouch which I take with me into my office or home – even if I leave my camera equipment in the car.

I’d like to heed the 40% storage method – but not all of my chargers accurately tell the battery capacity. And worse, when I’m running out for a night of exposures, I usually don’t have an extra hour or two to fully charge my workhorses.

And yes, repeated discharge and recharge of those batteries will diminish their life, but NOT as fast as fully loaded batteries baking at a mild 90 degrees or more.