Making a tachometer for a grinding / polishing machine for telescope mirrors

When making a telescope mirror on the machine, two parameters are important: the rotation speed of the mirror, and the rotation speed of the overarm eccentric. Other environmental parameters also matter: temperature and humidity are foremost here. To more easily monitor and display these variables, I've built an electronic device that collects this data and shows it on the control panel. This is how to build the device.


How to see Sirius B

Note - this blog post got noticed and was reprinted by EarthSky:

Sirius is the brightest star in the night sky, visible anywhere on Earth except the far North. If you live in the northern hemisphere at a temperate latitude, Sirius is that very bright white star due south every winter in the evening. But did you know that Sirius is also a double star? The companion, Sirius B, also known as The Pup, is a very small star orbiting the primary, and can be seen using amateur telescopes, even small ones. It's not an easy observation to make, but it can be done if you follow certain guidelines. Here's how to do it.


I had no idea just how big the Solar System really is

So, we did a "science project" today, the kids and me. We made a scale model of the Solar System, out on the street, to get a visual impression of its true size. It was pretty amazing. It's a very easy project to do, takes a couple hours, and it's a lot of fun.

The Sun was a regular soccer ball, 23 cm (9") in diameter. Everything else was made to scale.

Mercury was a tiny 0.8 mm grain of sand, barely visible, about 10 m (30') away from the Sun.

Venus was a larger 2 mm grain of sand, 18 m (54') away from the Sun.


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