Spotty Sun!

Moon orbit Illustration by NASA/Spaceplace

I was doing my regular daily circle of on-line reading when I happened to catch Mr Bad Astronomer's post about today being the Earth's perihelion day!  Since the Earth and all planets, for that matter, orbit in an ellipse as (most of) you know, perihelion is the point of the orbit where the planet is at its point closest to the sun.  Reading Phil's post, interestingly, while the Earth's orbit is stable, the perihelion point can vary from year to year, mostly because of the Moon!  As the Moon orbits the earth, the Earth too circles the center-of-gravity of the system, called the barycenter, illustrated at left.  Because the Moon reaches the full phase in a day or so, the Earth is a little closer to the Sun than it normally is, and the phase of the moon can effect perihelion by a day or two...

As any blogger will tell you, you can get a lot more posts about certain concepts by having a variety of pictures in your library.  Like happening to catch the "smallest Full Moon" last January - I happened to have a picture of the "Supermoon" from 18 months earlier and could directly compare disk size for a powerful illustration!  So while I don't yet have a photo of the sun at aphelion, and I've never seen that comparison (!), you will likely see it here on July 6, the day that happens!

So getting started on that July post, I needed to take an image of the sun today.  I set up the TEC 140 on mount and tripod, along with the same solar filter setup I used 10 days ago to image the sunset. Even a casual glance at the Sun's disk showed a huge sunspot near the center - active region (AR) 2253. Sure enough, after an imaging session, I put on my eclipse glasses and found it was easy to see with the filtered naked eye!  The full-disk image at left was taken with the TEC 140 and Canon XSi on the non-tracking mount with 1/640th second.  You can see besides the new AR2253, there are lots of other, smaller sunspots as well.

Of course, with the image down-sampled for the web picture above, some of the data is lost, so a full-resolution image is shown here.  It is again the same single image as above, with just a little sharpening applied.  Click on the images to see a larger version.

It is always interesting to tell people that we are closer to the sun this first week of January while winter weather has us in its grip!  The effect is small, the eccentricity of the Earth's orbit is only about 3%.  Of course, the real reason for northern hemisphere winter is that the axis of the earth is pointed away from the sun and it appears lower in our sky, resulting in less illumination and shorter days, thus cooler temperatures. 

Come back in 6 months for a comparison of the sun's disk for perihelion/aphelion!