Yesterday was my first day on the Bicycle Astronomy cargo bike in many months. I rode to work and then to the grocery store to reprovision the Spartan Manor travel trailer.
When I left the store with three bags of groceries and loaded them into the giant pannier on the cargo bike, it was a beautiful evening. The western sky was a deep blue and Venus, following the setting sun, was shining at me brightly. The air was cold and crisp and dry. Overhead and to the South the Moon and Jupiter competed for attention.
My route took me past the house of my daughter’s friends, S (2nd grade) and B (fifth grade), both supporters of Bicycle Astronomy. B in particular has an interest in astronomy, and a few years ago she got her first telescope. I figured it was about their bed time, but maybe we could take a quick peak at Jupiter? I’ve been meaning to do this for a while, but planning astronomy in cloud-land is not easy.
I turned into the driveway and knocked on the door. They were just settling down, and their Mom had them quickly dressed and out the door. We set up B’s little telescope on a bench and B used the red dot finder to zero in Jupiter. We looked at it first at low power, then medium power.
At first we only saw three of it’s four large, visible moons. It took a minute of squinting (I think they might need better eyepieces, Mom and Dad!) but I found the fourth, tucked into the glare around the disk of the gas giant planet itself. B and S both could see it, once I told them where to look. S is doing a project on the solar system in school and she remembered one of the Galilean Moons’ names. B remembered another. I added the last two.
We took a quick look at the Moon (oohs and ahhs) and then it was time for the ladies to scamper back off to bed. I used their Mom’s computer to pull up a little Java applet that shows the positions of Jupiter’s moons for any given time and date. I wanted the kids to know the names and order of what they were seeing when they had a moment this morning.
Callisto was the moon that was hiding near Jupiter! The view in a Newtonian reflector looks like this, but upside down. So turn the computer over to see exactly what we saw through the eyepiece. If you have a desktop, sorry!
If the ladies had gotten up in the very early morning, and snuck out onto the porch to take another peek at Jupiter, now very much to the west, here is what they would have seen:
And, if they went out tonight (April 1st) at the same time as last night, here is what they would see:
What explains these observations?
I never get tired of looking at, or showing people, Jupiter. Saturn gets more wows, but the telescopic view of Jupiter and its four large moons is an image that changed the course of human history. Here’s a hint: we call them Galilean moons, after Galileo, the great astronomer…