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Fall SAVY 2012 Week 5: Astronomy

Posted by on Monday, October 22, 2012 in SAVY blog.

Week 5: Astronomy

Another fun week doing Astronomy at SAVY!

While we sadly didn’t get to go out looking at the Sun with our solar filters (for the second week in a row!), we had lots of other things to talk about!

First, we discussed the possibilities for having a clear night for the Adventure Science Center Star Party that we piggy-backed on. The websites we used were WeatherSpark-Nashville and ClearSkyClock-Nashville. Fast-forward to Saturday night and those of you I saw on that CHILLY evening were having a great time 🙂 We’ll try to have an on-Vanderbilt-campus star party on FRIDAY, October 26 – more info as the date gets closer.

After finding out about observing, we used Stellarium again to look at how the North Star changes over time! Just turn off the atmosphere, push “Fast Forward” a few times, and watch the sky rotate around the North Star. Then change the year (by thousands of years!) and see if Polaris is still the North Star. We observed this and it is evidence for precession (i.e. Earth’s tilt is wobbling around just like a top wobbles just before it falls down – NASA animation here and a good blog post here) – Wikipedia “Axial Precession” and “Precession”. The big thing to remember is that it’s not that Earth’s axial tilt changes from ~23.5deg, it just changes where it’s pointing. Oh, and because there is no friction in space, Earth will never “fall down” like a spinning top would. Another thing we noticed here is that over thousands of years, the positions of stars change because we’re all going around the Galactic Center and some things are closer to us than others so it seems like they move faster. Stellarium is awesome 🙂

While we were looking at Stellarium, the students wanted to know about particular stars and then we started talking about how far away they are and that the number of light-years at star is from us tells us how long it’s taken that light to get to us! It boggles the mind that we’re ALWAYS looking at the past! We also talked about how long WE have been sending signals into space and I (belatedly) found a neat cartoon to show this (original here, with some commentary here). We also talked about why we can see the beginning of the Universe – ask your kid!

One of the most popular topics in astronomy is black holes and so we needed to talk about it! But as a little aside, we started talking about astronomical symbols (because I was using the symbol for the Sun to talk about the large masses of black holes) – one can find the major symbols on this Wikipedia page. In our black hole discussion, we talked about how black holes bend spacetime (diagrams here and here) and about how big the Schwarzchild Radius is (i.e. how close you can get and not be able to get away) – for a black hole the size of our Sun, the S.R. is only 3 kilometers!! You have to AIM for that black hole! We also talked about evidence for the fact that gravity bends light – it’s called “gravitational lensing” (images here and here). If you want a pretty good (if a little dated) website for basic black hole information, try here.

After a break from all of that space-time warping, we went to the computer lab to learn about planets going around other stars (a.k.a. extrasolar planets or exoplanets). We looked at the definitive website for known exoplanets called We looked at the data tables, made histograms and scatter plots and just kind of played around with what is out there. Astronomy is a huge subject and there is a great deal of information just online that you can “harvest” for projects if you just want to try.

Remember that we’re hopefully going to observe on FRIDAY (not Saturday as Vandy’s Homecoming game starts at 6 p.m.). More info to come!

– Dr. G 🙂


  • Norwood Boyce

    October 11th, 2013

    This is a great topics about Astronomy guys!!