Thursday, July 30, 2009

Stellarium – Your Personal Planetarium

Late summer and early fall is a great time to get kids to look out the window of Space Ship Earth. Before even thinking about buying the kids or grandkids a telescope (subject of a later post), teach them first how to find the visible planets, the brighter stars, and the major constellations so they can comfortably move around the night and early morning sky.

Knowing how to locate objects with the naked eye is a prerequisite to learning how to use an optical telescope. Learning how to use Stellarium will teach kids (or interested adults) the basics of backyard astronomical observation. Kids need to know the basics so they can develop enough of an interest in astronomy to warrant buying them a telescope.

And, Stellarium is free! Go to and download the Mac or Windows version.

I will now help you set Stellarium to your geographical location and then take you through an example of how to use the program to set up a specific viewing scenario.

Assuming you've downloaded Stellarium, open the program by double-clicking on its icon.

Press the F6 key to open the Location window.

In the upper-right corner, type in your location. Your location (or locations near the one you typed) will appear in the window on the right. Move the cursor to this window, and click on the correct location (or nearest location). This sets Stellarium to your latitude, longitude, and time zone. ***IMPORTANT*** Be sure to check the Use as default box in the lower-left corner so that Stellarium loads your location every time you open the program.

Press the F5 key to bring up the Date and Time window. You can set Stellarium to any date and time, but for the viewing scenario I want to create, click on the small arrows to change the numbers in your Date and Time window to correspond to the numbers in the following picture.

It is now 5:40 AM. August 27, 2009 in Stellarium. Use the left or right arrow keys to look due east. This is what you will see.

The planets Mars and Venus are visible along with Orion's Belt and the bright stars Procyon and Sirius.

That's all there is to it. Use the Date and Time window to create any scenario you like, and then go outside and look at the real thing!

There are many other features that you and the kids will enjoy exploring.

For example, here's an uniteresting screen shot of the moon and star cluster NGC 6231(object 6231 in the New General Catalog of deep space objects).

Press the "c" key and the outlines of the constellations appear. That's a bit more interesting and informative.

Press the "v" key and the names of the constellations are added to the oulines. Okay. Now I have an idea as to what part of the sky I'm looking at.

Press the "r" key and artistic representations of the constellations are added to the sky. All of these keys are toggles so pressing them again turns off the features.

Documentation is included in the download but I made a list of the most-used functions. If you would like a PDF of Stellarium Quick Keys, email

Many thanks to Roger, a good friend, for getting me to think about an astronomy post. Also, many thanks to the Stellerium developers [listed on the Home page] for their gift.

Sunday, July 26, 2009

Water-grow Animals

Animals molded from polyacrylamide (the water-absorbing polymer used in diapers) will dramatically increase in size when immersed in water for several days. Such animals I call water-grow animals.

A great measurement activity for kids is to daily measure, record, and graph the change in length and width of a water-grow animal. Last summer, our two oldest grandkids, Joshua (Grade 3) and Jordann (Grade 2) placed a 15-inch alligator in grandmother’s bathtub and a week later it had grown to a length of 48 inches!

The kids liked the activity so much they wanted to repeat it during a recent visit. Only this time, each would choose a different animal.

Jordann chose a colorful frog that would fit in the palm of her hand.

Joshua liked a venomous cobra.

Before placing her frog in water, Jordann measured and recorded its length and width. As you can see in this picture, the frog is 3 1⁄2 inches long.

At this age, measuring to the nearest quarter-inch is sufficiently accurate. Later on, when measurement comparisons are made (e.g., the change in length from day to day), adding or subtracting quarters is easy for kids to compute.

Joshua’s snake measured 12 inches in length (no attempt was made to straighten the snake).

They recorded measurement data in separate tables and then graphed the data. I designed and printed the data and graph pages for them.

If you would like PDF files of these pages, email

Grandmotherscience was diligent in making sure Joshua and Jordann recorded and graphed measurements at the same time every day so that a daily growth rate could be computed.

At the end of their six-day visit, Joshua’s cobra had grown to over 48 inches!

And Jordann’s frog would no longer fit in the palm of her hand!

Both the snake and the frog are now drying on the patio and the kids will be eager to see if they return to normal size when they return in three or four weeks.

Water-grow animals can be purchased at most large retail outlets. If, like grandad, you like the convenience of ordering online, the following link has a large selection and good prices for water-grow animals.

Grandadscience will happily post water-grow animal pictures and measurement data from other kids (first names only).

Besides length and width, what other measurements could be made on a water-grow animal? What questions could be asked?

Friday, July 10, 2009

Figurate Numbers-Part 2-Pyramid Numbers

I introduced figurate numbers (see the May 2009 folder) as a hands-on way to introduce kids to the mathematical beauty and number patterns that can be discovered by arranging objects according to a rule.

As learned in the previous post, the rule for forming triangular numbers is to successively sum the counting (natural) numbers, starting with the number 1. How the first four triangular numbers are formed is shown in the following diagram.

In one of the April 2009 posts I described Paula’s Puzzle. Four golf balls are glued to form a triangular-based pyramid. Five of these form a larger, 20-ball pyramid (see below). The puzzle is to figure out how to build the larger pyramid from the five smaller pyramids.

Is there a simple relationship between the triangular numbers and Paula’s Puzzle? The answer is “yes” and the kids can easily demonstrate the relationship.


You need a glue gun and twenty plastic practice golf balls. The golf balls cost a couple of buck a dozen and are available at any of the chain stores.

If your kids constructed Paula’s Puzzle, then they already know how to safely use a hot glue gun. If not, this is a good time for them to learn.

Have them build the second triangular number (3) by gluing together two golf balls and then gluing the third in place as shown in this picture.

Help them to build the golf ball models for the triangular numbers 6 and 10.

Once the kids have built the models, have them arrange the models in order, as shown below.

Ask them to build successive triangular based pyramids. It will be so easy for them to do this that they will think it’s trivial. Oh, if only we could convince them much of math was as easy to do!


Triangular numbers are made by successively summing the set of counting numbers and pyramid numbers (tetrahedral numbers) are made by successively summing triangular numbers.

Give the kids a blank sheet of paper and help them make a record of the relationship between the triangular numbers and the pyramid numbers. Use the following table as a guide.

Here’s a short video that illustrates how pyramid numbers are built from triangular numbers.