The Excel plots how-to document I use for my classes is at www.astronomynotes.com/Excel-plots-howto.htm (case sensitive!) or as seen below. A word of warning I give my students: "Computers are extremely stupid; dumber than a grasshopper. They get easily confused and do precisely what you tell them, not what you WANT them to do. Follow the instructions without deviation or you could get Excel very confused. For example, click the <Next> button ONLY when the instructions tell you to do so."

Nick Strobel  nstrobel@bakersfieldcollege.edu

Astronomy Homepage:

http://www.astronomynotes.com

First make sure your time data is in 24-hour military time mode (so 1:30 PM would look like 13:30, etc.)!

1. Select just the data in the two columns you want to plot (e.g., the time and the altitude data). Do NOT select the entire column, but just select the numerical values.
2. Click on the chart wizard button in the toolbar (icon looks like a bar chart)
3. Under Chart Type, select the XY (Scatter), and then the sub-type that has the data points connected by smoothed lines. Click the <Next> button.
4. In the Chart Source window, be sure the "Columns" button is selected. It should have the time values along the X-axis. If not, then get the proper columns specified under the "Series" tab. Click the <Next> button.
5. Give a descriptive chart title and axes labels. Do NOT click the <Next> button until you have done the next two steps!
6. Get rid of the grid lines by unchecking the boxes in the "Gridlines" tab.
7. Get rid of the legend by unchecking the "Show legend" in the "Legend" tab. Click the <Next> button.
8. Choose the option that puts the chart in a new sheet. Click the <Finish> button.

Now in the Chart sheet you have to get Excel to make the graph look like a sensible scientific plot with a decent range on the X and Y axes and proper scaling of the axes. Here's how:

1. Double-click on the X axes. A "Format Axis" box will pop up. In the "Number" tab, select the option that puts the time in standard military 24-hour mode (so 1:30 PM would look like 13:30). Do NOT click the "OK" button at the bottom until the end of step 6 below!
2. In the "Scale" tab, unselect the "Minimum", "Maximum", "Major unit", "Minor unit" boxes.
3. In the field next to the "Minimum" box, enter the start of the time hour before your first shadow. For example, if your first shadow was at 9:45 AM, enter "9:00" in the field.
4. In the field next to the "Maximum" box, enter the start of the hour after your extrapolated sunset. For example, if your curve would extend to zero altitude at 7:32 PM (= 19:32 in 24-hour mode), enter "20:00 in the field.
5. In the field next to the "Major unit" box, enter 1:00 (note the colon!)
6. In the field next to the "Minor unit" box, enter 0:10 (note the first zero and the colon!). Click the "OK" button at the bottom.

If the Y-axis on your altitude vs. time plot does not start out at zero degrees, then double-click the Y-axis and adjust the Y-axis range using the "Scale" tab in the "Format Axis" box---unselect the "Minimum" box and enter 0 in the field next to the "Minimum" box.

After you print your graphs, hand draw in your extrapolated altitude curve to 0š altitude to get the sunset time and hand draw in your extrapolated azimuth curve to the sunset time to get the sunset position.