Trying to explain to a four and six year old why it’s cold in winter can be a challenge. I was getting into a long-winded dissertation about the northern hemisphere being tilted away from the sun in winter… and losing them fast. SOLIDWORKS to the rescue! Yes, I know there are hundreds of videos on YouTube explaining this, and Bill Nye even did a pretty cool episode on it, but what fun is that? My kids love when I break out SOLIDWORKS at home and we make “cool 3D stuff” on the computer.

So we started making a scale model of the solar system. Seeing as SOLIDWORKS has a physical limit of 1000m^3, the scale of the sun and earth would have to be roughly 1:149M. At this scale, navigating the “solar system” and even finding the earth became exceedingly time consuming (though pretty neat to see how small the earth is compared to the sun). So I just made the earth a 1m sphere and used a point light as the sun. It gets roughly the same effect without all the big numbers!

By finding an image of the earth (thanks again Google) I created a decal and wrapped it onto my sphere. Of course, it was critical that I tilted the decal 22.5deg, to actually show the seasons. Next, I created an assembly with the point light at the origin and a circle describing earth’s orbit. Again, very not-to-scale, but it’s OK.

Next, I used a Path Mate to describe the location of the earth on the orbit. Path Mate allows me to assign a percentage along the path [0% = Winter Solstice, 25% = Spring Equinox, 50% = Summer Solstice, 75% = Fall Equinox]. I made configurations of each of those values for easy switching. I also set up some camera views to see the effect better. With a “Pitch Black” background and PhotoView 360 rendering, it really brought the project to life for the kids and hopefully taught them a few lessons they will never forget!

### Let’s take a look at the results:

First, an overall view of earth’s orbit. Remember, the tilt of the earth stays in the same orientation all year.

Now a closer look at the earth at each of the locations.

### Spring Equinox (March 20th):

We can see that both the northern and southern hemispheres get the same amount of light.

### Summer Solstice (June 20th):

We see that the northern hemisphere is in more direct sunlight. Therefore, it is summer in the northern hemisphere and winter in the southern hemisphere.

### Fall Equinox (September 22nd):

Looks very similar to the Spring Equinox.

### Winter Solstice (December 21st):

We see that the southern hemisphere has more direct sunlight. Therefore, it is summer in the southern hemisphere and winter in the northern hemisphere.

This proved to be a fun little project to share with the kids.

It used extremely simple geometry mixed with some neat SOLIDWORKS tools and taught them about the seasons. Eventually I might put a star field in the background and make some nicer renderings and videos, but for now, I have to get back to real work!

Thanks for reading, and as always, Happy Modeling!