LEGO Technic 42179 Planet Earth and Moon in Orbit – Finally an orrery! [Review]

As time goes by and LEGO Technic adds more and more elements to its repertoire, it becomes more and more of a force to be reckoned with in the world of STEM toys. Nowhere is this more evident than in the recent addition to their lineup: the LEGO Technic 42179 Planet Earth and Moon in Orbit. Some form of orrery (a model of the orbit of planets and moons around the sun) has been on many wish lists for a long time, and finally the wait is over. The kit will be available March 1st and retail for US $74.99 | CAN $99.99 UK £69.99. Join us as we build the 526-piece model and see if it’s everything we’ve hoped for. 

The LEGO Group sent The Brothers Brick an early copy of this set for review. Providing TBB with products for review guarantees neither coverage nor positive reviews.

Unboxing the parts, instructions, and sticker sheet

The box is on the smaller side. The front features the new “SPACE” banner with the classic logo, while the back shows how the model works.

Inside are 4 numbered paper bags and an unnumbered plastic bag. Loose are the new sphere halves for the sun and a couple of large Technic rings. The numbered bags have smaller numbered bags within them, all with their own QR codes and part numbers printed on them. It’s cool to see the switch to paper finally happening.

Because this is a basic Technic set and not an exclusive 18+ set, the instructions don’t have the details on the first several pages that we’ve become accustomed to seeing in those. It’s unfortunate, because this seems like a situation that would really benefit from some interesting information about the subject matter.

As for the stickers, we get a small sheet that includes the months and moon phases.

The build

First order of business is building the base for the orrery. It includes large black banana gears and heavy molded wheels that we haven’t seen for over a year. The center ring is in that lovely new red-orange color.

From there, we quickly start building a mechanism that includes a series of gears. The large banana gears that compose the outer ring are simply to provide a stable base, but are not used at all in the mechanisms.

Throughout the model gears are strategically placed in order to create a system that is being geared down (slowed from input to output). In the GIF below, you can see the beginnings of this system. A 36-tooth gear at the bottom will serve more than one purpose. Here, we have roughly a 5:1 gear ratio.

The sun will sit upon a framework that includes a large turntable.

From the previous group of gears, the top drives the turntable (by a further reduction of over 1.6:1), while the bottom is connected to an axle and gears that come up through the center to rotate the sun. In essence, the sun is being spun while also rotating, but the turntable (rotating) portion’s greater purpose is actually to rotate the large arm that the Earth is attached to. At this point a bevel gear also transfers the the motion perpendicular to the crank, which, of course, is actually the driver of the entire string of mechanisms. The GIF below is as fast as I could spin the crank, multiplied by 2.5.

Next, the upper ring is added and slopes are used to adorn the sides while also providing support. Beauty is sort of in the eye of the beholder here. Some might like that the core gets a bit covered, while others might wish all the gears were exposed for viewing.

After that, we turn our attention to the large arm. A pearl gold connector is used as a guide to provide stability, and we’ll come back to that in a moment.

The mechanism that sits just below the sun needs to transfer rotation on a perpendicular axis, while also going around that axle to feed motion to the sun. Bevel gears are used to accomplish this and a couple others are used to increase the input speed by a ration of 1:3. A small turntable at the top does not move but simply allows for the axle to pass through the center while still providing support underneath.

With that, we attach this chunk to the base and apply the month stickers to the upper ring.

The sun is added next. It’s composed of two new bright light yellow 11×11 sphere halves.

Once again, the GIF below shows an up-close look at the mechanism. Like the above, this is as fast as I could turn the crank times 2.5. December to February actually takes at least 12 seconds.

The Earth and moon part of the mechanism looks like it belongs inside a clock.

This is where it becomes even more complex and intriguing, with more than one things happening at the same time. Like the sun, we have both spin and separate rotation at play.  There is a gear reduction rotating the moon, and a gear overdrive (increase in speed) rotating the Earth.

The moon is represented by a little light bluish grey ball joint, while the Earth is made by a smaller version of the sun sphere (5×5), printed with the continents. A universal joint allows it to be tilted on an angle, just like the real thing. Additionally, a pearl gold tooth marks the moon phases.

While building this set, you do realize the importance of closely following the directions to make sure that everything lines up correctly. Fortunately there is a helpful diagram in the instruction manual for the final connections.

The completed model

With that, the orrery is finished! It truly is a marvel of LEGO construction. You can see from the photo and GIF below that there is the slightest bow to the arm. It’s not bowing the pieces, just using every bit of leeway there is in the connection points. The arm is relatively heavy, and the guide support that was mentioned early on is certainly needed. Regardless, it looks pretty nice and is compact enough to fit on a shelf for display.

Like the other GIFs, the one below is sped up significantly. Even with the use of a motor it takes several seconds to complete a revolution. Just like it should!

Conclusions and recommendations

You might be wondering, is it accurate though? And I’m glad you asked, but I cannot provide a 100% straightforward answer. If you make extra sure to line everything up perfectly and turn the crank at a reasonable speed without getting wild, yes it is surprisingly accurate. Considering it’s made within the constraints of LEGO, this is a true feat that is commendable. But there is give within the system. If you’re a couple gear teeth off in your final placement you could be the tiniest bit off. If you spin the crank as fast as possible, there might be a bit of slippage. The largest margin for error is if you mess with the Earth directly, trying to spin or rotate it by hand. This can create variability. Over time even if you’re kind to it, it might fade out of accuracy. However, generally speaking, I would give it good marks.

Some of us have asked for an orrery for a long time. A small few have even made their own. It was high time that LEGO designers gave it a whirl (no pun intended), and I would say they didn’t disappoint. Overall it’s a fun model to both build and admire. While an 18+ model would’ve been really cool to see, I’m not disappointed at the younger age suggestion. It feels like a fun kit for any experienced builder to tackle, and I would recommend it highly to anyone with interest.

If you like Technic and/or Classic Space, you’re in for a treat! We have loads of reviews coming down the pipeline within the next week. Stay tuned and follow along in our reviews archive!

LEGO 42179 Planet Earth and Moon in Orbit will be available starting March 1st and retail for US $74.99 | CAN $99.99 | UK £69.99.

The LEGO Group sent The Brothers Brick an early copy of this set for review. Providing TBB with products for review guarantees neither coverage nor positive reviews.

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