Watching an Eclipse From the Earth

The Set-up: A Tutorial

This is the first of two adventures about the total solar eclipse of July 2, 2019. In this one, we will be watching the eclipse in the conventional way, from the Earth.

The adventure will start with a series of short videos in tutorial format, in which we set everything up to watch the eclipse. You don't have to watch these, but I you want to learn about how to use the Planetarium, they will be the most important part. I suggest that you work through the Stargazing Tutorial before you watch them, at least its first segment about entering the planetarium for the first time. As usual for tutorials, I suggest that you open the planetarium in another window and follow along.

In the last video, we will just watch the eclipse, from just before the Moon first overlaps the Sun until just after totality. That video is intended as standalone, so if you just want to see what the Planetarium can do, start with that and just enjoy it.

So enter the planetarium and let us begin!

1. Initial Setup and Location.

  1. Right click to open the Control Panel. I suggest that you click the "All Defaults" button at the bottom to start from the default configuration (as I am doing). At least get into Stargazing mode by setting that in the Mode drop menu at the top.
  2. Left-click on Viewer Location to open that section. Set your location to 34.4 degrees S (-34.4) and 141 degrees west (-141). We can do that by typing in the boxes. Now left-click on Viewer Location again to close it.
  3. Leave the Control Panel open.
2. Initial Date and Time Setup.
  1. Open Date and Time and left-click Stop Clock. We will start the clock again When we have everything ready.
  2. Set the timezone offset to 0 so we are all using GMT, which is UTC + 0 hours.
  3. Set the date to July 2, 2019 (2019-7-2) at about 16:15 hours.
  4. How did I come up with this place and time? First, I want totality to occur when the Sun is low in the sky, so I can include the eclipse and the ground in one view. To make that happen, I want to be far to the west so that the eclipse will start soon after sunrise. As long as the sun rises after the moon, before it is eclipsed, there will be some latitude on which the eclipse will be total. We can find that latitude by feeling around for it in a systematic way – adjusting the latitude and the time until we find it.
  5. If you try this yourself, maybe for other eclipses, be warned that, in the planetarium, positions of objects in the sky are only accurate to about 1/10 of a degree. If you compare our positions and times for the eclipse to those actually observed, they will not be quite right. They may be off by several degrees and as much as half an hour.
3. Set Sun and Moon to have their real size.
  1. 16:15 hours is a good time to start watching the eclipse, but to continue setup, let's move forward in time to just after sunrise and move the Sun to where we can see it. It looks like the Sun is already almost totally eclipsed! But that's not right.
  2. To see what the problem is, left-click on Planets to open that section. Sun/Moon magnification is 5, which means that Sun and Moon appear 5 times larger in diameter than they should, given where we are and where they are. For a realistic eclipse, we need to turn Sun/Moon Magnification down to 1 – no magnification – so that they are their real size. Otherwise, the eclipse will start much earlier and last much longer than it really should. Left-click on Planets to close it again.
  3. Since Sun and moon now look rather small on screen, let's turn star size down, too, so the brighter stars don't look as big as the Sun and Moon. We do that by opening the Star settings and turning Brightness Boost down. Brightness boost primarily controls how bright stars are, but for brighter stars, the planetarium replaces brightness by size, so reducing brightness boost gives the brighter stars a smaller, more realistic size. Close Stars by left-clicking on that heading again.
  4. Our tutorial about the Control Panel goes into Planet and Star settings in more detail.
  5. Now, the Sun and Moon look quite tiny, so let's open View on the Control Panel and zoom in until Sun and Moon are a reasonable size. A zoom of 5 would make them the same size as when we started, but we will use 3.5, because we want the Sun and Earth both to be onscreen when the eclipse reaches totality. 3.5 is a number that will accomplish that. Close View again.
  6. Note that we can see the Moon against the black sky. That is because the near side of the Moon is enjoying a full Earth and the light reflected by the Earth faintly illuminates the Moon.
  7. It also helps that, in the Planetarium, the Sun is not nearly as bright as it is in the sky, so its light does not dazzle us when we look at the moon.
  8. Adjust the view so the sun will rise a bit to the right side of the screen, because it will ascend diagonally across the middle, more or less parallel to this line of latitude. Also make sure that the Earth is clearly visible at the bottom.
4. Final Setup.
  1. Now let's finish setting up.
  2. Put the time back to 16:15 GMT.
  3. Set the time rate to 60. That way each hour of the eclipse will go by in just a minute in the planetatium, so it won't take very long to watch the eclipse.
  4. Finally, I suggest that you open Screen Decorations by left clicking on that heading. Turn off the Lines, the Labels, the Direction Markings and possibly the Onscreen Controls, so that fewer things are cluttering the view. If you want, keep the Onscreen Controls on so you can see the time. I will turn them off. Close Screen Decorations by left clicking on the heading again.
5. Watch the Eclipse.

This section is written to be watched as a stand-alone video, independent of the preceding sections, so there will be some repetition of their material.

This video may look better full screen.

  1. We are somewhere in the South Pacific, southwest of Pitcairn Island. It is just before sunrise on 2 July, 2019 and we are set up to watch a total eclipse of the Sun from when it first starts to the end of totality.
  2. The clock is stopped. When we start it, the Sun will rise and the eclipse will begin just after that. The clock is set to run at 60 times its normal rate – so that each hour of the eclipse will go by in just one minute.
  3. We start the clock and Dismiss the control panel.
  4. In Planetarium World, we do not model the Earth's atmosphere, so the sky is always dark, the stars are always visible, and sunrises are not red, though they can still be dramatic.
  5. The eclipse is starting.
  6. Note that we can see the moon, faintly illuminated by the full Earth that is shining on its near side.
  7. What we see on the horizon is some combination of cloud and sea. As we approach totality, the horizon will gradually get darker.
  8. At totality, it briefly gets very dark - nighttime dark - until totality ends.
  9. As the Sun and Moon sail off the screen, the eclipse is ending, so I'll end the video here. Thanks for watching.
  1. Find a place even further southwest where the sun comes up totally eclipsed. Most total eclipses start when the Sun comes up somewhere totally eclipsed and end when it goes down somewhere totally eclipsed.
  2. Look up a recent annular eclipse and try watching that.