Total Solar Eclipse

The appearance of a total solar eclipse is so singular that it is impossible to appreciate it without having seen it for oneself. Unexpected eclipses have changes history in the past, although they can now be predicted. Even having an eclipse forecast in hand does not reduce the impact of the experience on witnesses.

And total eclipses are rare. The most recent time the moon’s shadow fell properly across the United States was in February 1979.

But just as eclipses can be predicted, they can also be simulated in the SciDome planetarium environment. Here is how to simulate the upcoming Great American Eclipse of August 21st, 2017 in your dome.

First you need to set the correct date in Starry Night Dome. Starting from the home location of your planetarium, if you are located in the United States, some time on August 21st the Sun will be at least partially eclipsed, but it probably won’t be totally blocked out.

An accurate simulation of a partial eclipse in SciDome without any magnification will probably look like a normal day as the Sun moves from the eastern to the western horizon across the blue sky and sets. Likewise, in the real world it is possible to not notice the progress of a partial solar eclipse unless the fraction of Sun covered is well over 50%. The shadows cast on the ground by sunlight shining through tree-leaves can reveal a partial solar eclipse, but the reduced amount of sunlight in the sky is only subtly perceptible.

Two steps need to be taken to appreciate a partial solar eclipse in SciDome. First, use the keystroke [Ctrl-D] to toggle daylight off. This will improve the contrast between the Sun and the black sky background.

If you are close to the zone of totality, looking at a hemispheric view, the blown-up image of the Moon we normally use in SciDome to show its phases will probably appear to cover the Sun totally during the partial phases, and toggling daylight back on again with the same keystroke will show that the remaining sunlight is still illuminating the sky above your location. Therefore please right-click on the Sun and select “Magnify”. This will center the Sun on the front of the dome and magnify it so that it’s zoomed in. In this way the “Enlarged Moon” effect used at wide fields of view is eliminated. Now the “bite” out of the Sun is properly simulated. Run time forward and back in steps of up to 300x actual speed to follow the event from start to finish.

To simulate the total phase of this solar eclipse, identify an observing site that will be in the zone of totality. Because the path will neatly bisect the United States, the nearest place where the eclipse will be total is never more than three states away from your location (excepting New England.)

Path of the 2017 Total Solar Eclipse

The following state capitals will be in the zone of totality:

  • Salem OR
  • Lincoln NE
  • Jefferson City MO
  • Nashville TN
  • Columbia SC

Major cities including Kansas City, St. Louis, and Charleston will also be in the zone. You can find alternate locations with the interactive Google Eclipse Map.

Hit the “Viewing Locations” button and enter the name of the town, or its latitude and longitude, or its ZIP code. Once Starry Night has “flown to” your destination, the northern horizon will probably be on the front of your dome, but you can still right-click and “Center” the field of view on the Sun without magnification, and then step forward and back in time in intervals of hours or minutes to find the moment when the sky starts to incrementally darken. The keystroke to advance in 1-hour steps is “h”, and to reverse in 1-hour steps is [Shift-h]. To advance in 1-minute steps, use the “t” key, and to reverse in 1-minute steps, just add the [Shift] key.

Starry Night will not appear to display other than a normal daylight sky until about 8 minutes before totality. During those 8 minutes the sky will start to appear darker and more violet, and extra objects will start to appear in the sky: Venus first, followed by the brighter stars. Then the darkening will accelerate and go into totality for up to 160 seconds of simulated time. The horizon will accurately represent the eerie appearance of the “360° Sunset”, and the occulting Moon will reveal the red solar chromosphere and the white corona surrounding it. After totality is finished, the appearance of the unmagnified sky will take about 8 minutes to return to normal. The partial phases and totality can be simulated accurately with magnification.

Shadow cones, a Starry Night feature to illustrate eclipses

Because SciDome can also accurately simulate travel through space, right-click on the Sun during the eclipse and select “Go there”. Without specifying a surface location, Starry Night will arrive at a point somewhere above the Sun’s surface, with no Earth or Moon in sight. Type in “Earth” in the Find Pane’s search engine field, and then you can right-click on it and select “Magnify”. The disk of the Earth should appear centered on the dome with the far side of the Moon superimposed on it, with the Moon’s shadow being cast on the United States below. By right-clicking on the Moon and selecting “Shadow Cones”, the dimensions of the shadow falling on the Earth will be demonstrated. Step forward and back in time with “t” to see the shadow move across the disk of the Earth.

Right-click on the Moon again and select “Orbit” to show the Moon’s orbital path falling in front of and behind the Earth from this observing location near the Sun. Zoom out a couple of degrees to see the whole arc of the Moon’s orbit to the left and right of the Earth. The keystroke “m” and [Shift-m] can be used to step forward and back by intervals of months, demonstrating that the Moon’s orbit is slightly tilted such that it rarely creates the perfect syzygy between the Earth and Sun to create a solar eclipse.

Eric Briggs

Eric Briggs

SciDome Support at Spitz, Inc.
Eric has been an expert user of the Starry Night astronomy simulation software since its original release in 1997. He joined Spitz in 2008, providing support and training for Starry Night Dome and other software on SciDome planetarium systems.

Eric is the co-discoverer of 10 supernovae (and counting).
Eric Briggs

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