Monthly Archives: March 2012

Astronomically, it IS an early spring!!

So I read this article and I had to share it with you – I think it’s very good :)

Article:  Spring Arrives With Equinox Tuesday, Earliest in Over a Century
by Joe Rao, Skywatching Columnist

As an introduction, here in Nashville, we’ve been experiencing a really mild spring – personally, I’m pretty happy about it because I go observing with the lab students a lot and it’s been so nice to not have to bundle up ;)  Thus we’ve been having an early spring meteorologically.

But let’s think about what the start of spring means ASTRONOMICALLY.  The start of spring is technically the date of the vernal equinox which technically is when the Sun’s position in the sky goes from being in the southern celestial hemisphere to being in the northern celestial hemisphere.  You can see this with Stellarium!!  Plus you can see how the actual location of the equinox in the sky (comparing it to the constellations) changes over time – this is called the precession of the equinoxes and it is why we are entering the Age of Aquarius!

Heliocentric vernal equinox

The vernal equinox location (see arrow) according to the heliocentric perspective.

Geocentric vernal equinox

The location of the vernal equinox according to a geocentric view

Here’s a lovely graph from Wolfram Alpha that shows the date of the vernal (spring) equinox for certain time periods (see axes ;) ):

Date of the vernal equinox VS time - from Wolfram Alpha

Note that we’re bottoming out for our cycle in the left graph (stupid axes if you ask me so it is kinda hard to see).  The short-period cyclic nature on the left shows the “resetting” every leap year and then the big jumps on the right plot show the effect of not having a leap year during century years (i.e., 1800, 1900, 2100, 2200) unless those years are divisible by 400 (i.e., 2000).  To learn more about this (and to see a better graph), go to Wikipedia :)  Dudes, on Wikipedia, I learned about the Iranian calendar which has 8 leap days in every 33 year time period – it’s more accurate :)

Anyway, the aforementioned article is a good article – Dr. G approved! ;)


Awesome Planetary Formation Videos

Computer Model of Planetary Formation

In class on Monday, I showed a whole bunch of videos that show planetary formation – some showed certain parts better than others but they all are pretty awesome.  Just in case anyone wanted to look at them again, here they are:

  • Short, beginning of formation (from gas cloud to disk) from ESA – here
  • By NASA for the James Webb Space Telescope, uses data from computer models – here
  • Narration by Harrison Ford, I like that it has some timescale information in it, part of a larger series – here
  • From “Space with Sam Neill” Episode: “Star Stuff”, I really like how this one is done (I started it at 1:27) – here
  • If you liked the “Formation of the Moon” video from the end of class (it does happen to be one of my favorites despite the speeding up of some events that they did), it is here


Below is an image of the Orion Nebula (we can see it during our observations this semester ;) ) from the Hubble Space Telescope showing some of the protoplanetary disks that have been found in this nebula.  Look!!!  New baby planetary systems! :)

Click to go to the Astronomy Picture of the Day website for this image.

"Proplyds" (protoplanetary disks) in the Orion Nebula

Go outside on March 12 and 13!!

Mercury, Venus, and the Moon aligned. Taken from Paranal Observatory in Chile, March 2008 by Yuri Beletsky.

Right when we come back from Spring Break, we will be able to see a planetary conjunction!  You will be able to see Jupiter and Venus be within three degrees of each other and that’s an especially close separation and will be especially brilliant due to the biology of your eyeball – they will be so close that the “hi-def” part of your eye (the fovea) will be activated.  Here is a NASA article about it: Cold and Spellbinding: An Alignment of Planets in the Sunset Sky

Note that this conjunction is just the kind of thing that early astronomers were trying to predict using the Geocentric (Ptolemaic) model of the Solar System (with all of the epicycles and such).  To be honest, the geocentric model worked pretty well at the beginning, but errors combined over the centuries.  This conjunction is also the kind of thing that astronomers used the Heliocentric model of Copernicus to predict but was just as inaccurate due to Copernicus’ need for perfect circles.  Kepler’s models helped take care of the prediction problems thus the heliocentric model became the accepted model of the Solar System :)

To see how the conjunction works, I’ve put a line on this picture from the NASA/JPL Solar System Simulator.  Note that the line from Earth passes by both Venus and Jupiter :)

Solar System on March 12, 2012

Solar System diagram for March 12, 2012 to illustrate the conjunction of Jupiter and Venus. Note that Venus and Jupiter are along the same line-of-sight from Earth.