Tag Archives: transit

ISS Predictions

Last Updated: May 2, 2021

I had set up a program to automatically compute the ISS transits for different places and upload the results once a day – at around 11:00 am each day. See Zoom-Zoom for the impetus for this as well as references. However, it grew difficult and cumbersome to keep it working since the behavior was to run a Java process on my home computer, compute the coordinates and up load to my website.

But, the good news is… I found two resources that you can use that are quite helpful.
One is an Android App called ISS Transit Prediction Pro by Ed Morana. There may be an IOS version as well. I find it a bit clunky, but it does help to have a portable source to do predictions.  For example, here is the result of running predictions for the San Jose, California Area. There is a Jupiter transit and a lunar transit depicted. You can adjust how far you’re willing to drive, as well as the altitude of the transit.  What you can’t do, at least I haven’t figured out how, is to fine tune the prediction for a specific location. I imagine you can literally go there, or use Google maps (or set the location using the location in the app), but those options are a bit tedious.  See the web based app below for a comparison. The ISS Transit Pro app does allow you to save and share predictions – a feature that doesn’t exist in the Transit-Finder web page below.  ISS Transit Prediction Pro ALSO calculates transits of planets like Jupiter (see below). I’m eager to try getting one of those!

ISS Transit Finder (Web)

Another app is the Transit Finder (https://transit-finder.com). This web app is pretty slick. It combines Google maps click-ability with clear information, and it is pretty easy to fine tune something you’re interested in. It does have a problem in that as of this writing you will get warnings about trouble loading Google maps, probably because the authors would need to pay Google a fee to use the data Google offers. When you start this web page you can have it auto-detect your location, or select it on a google map. You then set your other options and eventually click CALCULATE to see predictions.

If it FINDs any transits (and it might not!) You see a page like this:

Transit Predictions within the starting Location up to the maximum selected distance from the “observer”

You’ll notice above that there are two predictions shown out of three, one crossing the sun (just grazing it) and another that is a “close pass”. The good news is, it’s very easy to turn that grazing hit into a centerline hit… and that close pass into a hit as well by moving to the correct location. Indeed, the grazing solar crossing shown is what I could have observed from my home! After fine tuning a bit, I discovered a public place with an open area from which to set up instead.

You fine tune the prediction by using “Show On Map”, then finding/zooming and clicking on the centerline in an area that may prove useful for observing. For example, here I’ve zoomed in and scrolled to the street just outside the Apple Campus in Cupertino, California. The first image shows the boundaries of visibility superimposed on the map. Red indicates solar transits, blue indicates lunar transits.

In the second image below the entire background is red because the area shown lies between the boundaries where the ISS grazes the sun. The center line is where the transit goes right through the middle of the object (sun/moon).

The map of predictions, zoomed in quite a bit.
It’s not easy to see here, but the Apple Park Duck Pond is near the middle of the Apple “Space Ship” office. The green dot reflects where I clicked. NOTE that it shows the exact time of the transit (here 09:32:32.60) and the length of the transit which is a teeny bit more than 1 second! You SHOULD RECALCULATE for the location.

Because of the (current) limitations in the Transit Finder map, it’s helpful to pull up a second window with Google maps zoomed into the same area. I find a satellite view is helpful. Note a couple of other things… the window shows the exact time, the direction to face (Azimuth: 100.1 degrees which is 10 degrees south of East), and how high in the sky to look (Altitude: 38.5 degrees). HIGHER is better because it means the ISS will be closer to you and thus appear larger.

Using Satellite view in Google Maps (and Google Street view), you can get a good idea if there are likely to be impediments to your view in the desired direction. Here you’re looking at the Apple Campus in Cupertino. The place I picked earlier was N. Tantau Avenue.. given all the trees, you may have to find a parking lot with a view East-South-East.

After inspecting the map all along the center line, I chose the PruneYard shopping center parking lot as the go-to place because it’s a large flat lot. I originally planned to be closer to the street, but discovered that tall trees made that impractical.

Some Final Thoughts and Caveats

Remember that the International Space Station (ISS) is an in-use craft. As such it is subject to orbital changes – both of the routine kind and for special operations like adjusting for docking, or moving to a higher orbit. Because the orbit is changed fairly often, predictions longer than a few days in advance may be in accurate. It is a good idea to recalculate a few days before, and even a few hours before a planned event. In the case of the May 2nd event, for example, the centerline of transit went through the middle of a local park 24 hours before the actual event, but recalculation on the morning of the event showed a change large enough to affect the quality of the image (it still would have been a grazing hit, but not a center hit).

It is MUCH easier to catch the ISS traveling across the face of the moon (when it is lit by sunlight) because you can easily follow it with your eyes. Catching the ISS crossing the sun is MUCH, MUCH more difficult. You literally need time that is accurate to 1/10 of a second or less. Fortunately there are apps for that, too. I use Atomic Clock on my Android. I use a shutter release cable, set the camera to high speed capture and try to hit and hold down the shutter button 1/2 second before the scheduled time. Much sooner and I risk filling up my frame buffer before the event starts. I plan to try this all again but instead of shooting still images, I’m going to capture 8K video (and use a higher magnification)

Interestingly, rough aligning your telephoto/telescope in the daylight with the sun is pretty easy to do by paying attention to the shadow that is cast on the ground.

Do not be afraid to play with adjusting off the center line. If you are shooting against a half full moon, for example, you may prefer the ISS to cross over the shadowed portion of the moon (or the lit side). You do get the most TIME to capture if you hit the center, however… but we are talking a difference of about 1/4 of a second or so!

Zoom Zoom

Last Updated: May 2, 2021

Phil McGrew had an out of this world idea. Capture the International Space Station as it hurtled across the face of the pre-dawn moon.  Great Idea – because it worked! How we figured out when and where to be to make this happen is described in the references below.

We agreed to meet at a spot that fell near the “blue line” (centerline) of the event: Muir Beach Overlook.  I woke up at 3:00 AM and arrived there at 4:45 AM. Everyone showed up on time at 5:00 am and we lugged our equipment into the conveniently located World War Two era machine gun bunkers which kept us out of the wind. There were 3 such bunkers and I took up residence in the closest one since I had the most gear to haul (and am the most lazy).

Bunkered Down for the Morning…

My companions picked two other bunkers, while Rick headed further North along the coast highway.  Note: Don’t let the term Highway confuse you it is a tortuous winding road hanging on sheer cliffs above the Pacific Ocean.


Resources and References

Notes about the Event

Before we left we had some discussions about whether the ISS would be visible and how to prevent it from “streaking” and smearing. The ISS is moving at  17,800 miles per hour. At its altitude from our location, that means it crosses the ½ a degree wide moon in under two seconds! At minimum I needed to select an fast enough shutter speed to max out the camera’s frames per second (more chances to get at least ONE hit) which on the Canon 50D is about 5.3 fps.  However we weren’t sure about the comparative brightness of the ISS compared to the moon.  If it were sufficiently dimmer then the moon brightness would overwhelm the ISS.

It’s interesting to try to get the ISS against both the lit and unlit portion of the moon – and we indeed got both.  The ISS trajectory and where you choose to go affects what you will see.  One of our group went farther north and got the ISS brushing the lit edge of the moon, though not crossing it.  This proved to be a quite interesting shot as it is definitely true that the ISS does not stand out well against the moon.

I went with about f/9. This is a rough calculation factoring the f/7.5 refractor  [80mm aperture with 600mm focal length], and a 1.4 teleconverter.  I had to tape over the pins on the camera-teleconverter or it would not let me take the shot “cannot communicate with lens” well – duh, the lens in this case is a TELESCOPE.  ISO 800, speed 1/500th of a second and the camera in BURST (continuous high speed exposure) mode.

We were not expecting a whole lot but were all high fives and thumbs up afterward.  Now that I’m groggy from sleep deprivation I’m wondering if driving about 4 hours round trip was worth 3 seconds of glory.  Yeah, I think so.

If you’re interested in catching the moon near your favorite STATIONARY object, I’ve got a well reviewed, well attended webinar on that.  Want to try some Astrophotography? I’ve got webinars and field shoots for that, too.  Join me and let’s do something unusual with night and low light shots.

For the latest predictions for the San Francisco Bay Area, Yosemite National Park, and Research Triangle North Carolina see this page.

Transit of Venus

Below is the the thought process I used to plan to take photos of the once-in-a-lifetime event – the Transit of Venus across the face of the sun. The event occurred on June 5, 2012. For some background, read here.

This is an especially useful tool:

A Goal

Get a recognizable foreground silhouetted against a large solar disk featuring the “dot” of Venus. To be useful, the sun needs to be large and the foreground recognizable. Here is what I actually achieved.

Drift Mode [composite]

With a Recognizable Silhouette (Here the Golden Gate Bridge)

Peek a Boo [C_037975]

Of course the sun would have to be higher so that the recognizable tower foreground would be visible as a silhouette. It should be possible to also process the shot like this one:

Rise and Shine [C_037951+77]

Imagine the “dot” on the face of the sun.

All this is possible if we catch the sun near sunset.  Sunset configuration rules out the Lick photo since that is facing east.

Important Factors

  1. Weather!
  2. Recognizable foreground
  3. Good distance from the target (to get a large sun diameter relative to the target)
  4. Long focal length.
  5. Weather!
  6. Sun azimuth will be about 300 degrees near set.

Possible Locations

  • Pigeon Point Lighthouse – alignment works. Fog might be a problem. NOTE the Lighthouse will be much smaller than shown here. Indeed, nearly the entire lighthouse will be present against the face of the sun due to the distance of two miles to the lighthouse.

  • Transamerica Building – probably won’t look like much in silhouette
  • Sutro Tower – wonder if it has the recognizableness, and if the thin towers will really show up against the sun.
    • Bristlecone Pine Tree – almost certainly doable somewhere!
    • Washington Monument?
    • US Capital Building?
    • Seattle Space Needle (Anything in Seattle is unlikely due to trees everywhere)

Locations Ruled Out

  • Most “mountain tops” as they are not easily recognized in silhouette – especially e.g. Half Dome (on the wrong side of the valley and so huge it’s not possible to get far enough away)
  • Golden Gate Bridge North Tower (mountains behind)
  • Coit Tower (unlikely – vantage is on Alameda and the Marin Headlands will be behind.)
  • Golden Gate Bridge South Tower (for the same reason as the North Tower)