Astronomy students hosted 35 first- through third-graders from Braintree’s Meeting House Montessori School for our fifth annual Astronomy Fair. Thayer students held planetarium shows, an observatory open-house, played astronomy themed games and activities and launched model rockets. Some images from this year’s astronomy fair, thanks to Joe DiVico for taking the photos.
Pictures of planets require very high magnification in order to see interesting details. This amplifies atmospheric distortion and makes precise focus tricky to maintain. Long exposures typical in astrophotography would result in a smeared subject if applied to planet imaging. Instead, thousands of short exposures are acquired and analyzed for good focus. Poor images are discarded, the remaining images are aligned and stacked. Stacking frames improves the signal-to-noise ratio in the resulting picture by a factor of the square root of the number of images in the stack.
Post-processing involves sharpening, some de-noising, exposure adjustments, image resizing and cropping. I used a similar technique to image Jupiter and sunspots. Future trials will involve imaging Saturn at higher altitudes to help with clarity and brightness.
The other day in Physics class we looked at the Sun through a couple of telescopes. The image was wavy, as if there were heat currents in the picture. That because there were: the atmosphere is an air mass with a lot of convective movement, especially when the sun is up.
Maintaining fine focus through a telescope at high magnification under these circumstances is difficult. This makes taking focused pictures of the Sun through a telescope difficult.
The way to get around this is to use video frame stacking. This morning I made a short video of the Sun; 1000 video frames at 30 frames per second. The original video shows a lot of waviness.
I used some software (Registax) to rank each video frame in terms of quality-of-focus. I threw away all of the wavy, out-of-focus frames, 963 out of the 1000. The remaining 37 frames were aligned, stacked, averaged and processed. Here’s the result- a good picture of a sunspot pair.
Sunspots are regions of the Sun’s surface that are somewhat cooler than their surroundings. Surface plasma gets trapped around magnetic field lines that pierce through the surface. Those field lines typically loop back into the Sun’s surface, which is why there are usually two spots together. One would be a ‘north’ pole, the other a ‘south’. Here’s a nice simulation showing this.
It can be tough to take pictures of the sky from the city, but with a little planning, clear skies and some equipment you can capture some nice shots. Tonight the thin waxing crescent Moon and Venus were close together in the southwest just after sunset. I set up my tripod, put on the telephoto lens and took a bunch of shots. I experimented with various ISO settings and exposure times so I could see the earthshine reflecting off of the unlit parts of the Moon’s surface. I set the lens to its maximum aperture so the depth of field would be as narrow as possible. Then the trees in the foreground would be far out of focus and would be less likely to block the pinpoint Venus. Lightroom was used to do some white balance adjustments, sharpening and cropping.
This image was acquired with a simple digital camera placed lens-up on a driveway. I set the camera to ‘manual’ so I could control the shutter speed, which I set to 30 seconds. I also set the ISO to 800 so I could pick up the faint stars. When I imported the image to my computer it didn’t look like much, but there were lots of stars hidden in the details. I brought these out with the exposure slider, and this is the result. The dim glow in the background is the Milky Way, the hundreds of stars that are visible are nearby, in between us and the center of the galaxy. If I attempted this near a city like Boston, the whole sky would be a diffuse glow of scattered streetlights.
We often see these on either side of the Sun here in the winter, but I have never seen these caused by moonlight. In order to pick up the faint colors in the arcs I had to completely overexpose the full moon, which is why none of the details are visible on its face. I stabilized the camera by placing it on the porch railing and shot for several seconds.
The arcs are part of a family of geometric patterns formed when sun or moonlight gets refracted by ice crystals in our upper atmosphere. This is a neat reminder that while it may be warm down here on Earths surface in the summertime, that it is always cold in the upper atmosphere! To learn more about atmospheric optics, check out this great page: http://www.atoptics.co.uk/
Yesterday we hosted an ‘Astronomy Fair’ at school. The twelfth-grade astronomy students prepared lessons and activities for 1st through 3rd graders from a local elementary school. Activities included observatory tours, planetarium shows, scale-modeling the solar system using the school’s large fields, and a science-fair type gathering in Alumni gym. Students experienced weight on different planets, did a ‘Where’s Waldo’ activity with a Saturn V rocket poster, played around with astronomy software on ipads and more. Attached is a slideshow.
This year we also hosted several boy and girl scout troops from around the South Shore, hosted students from Epiphany School in Boston and held a class for Braintree Adult Education.
Jupiter is the main attraction in the evening sky this fall. Look southeast shortly after dark and there it is- a bright and steady yellow-white planetary light. Tonight we were lucky to catch the space station flying overhead as well. We looked at Jupiter through the telescope, and then placed a camera at the eyepiece and took some pictures.
This first picture is of Jupiter with four large moons. The large disk at the center is the planet, and the four points of light near it are the four ‘Galilean’ moons of Jupiter. Close together are Io and Europa, and on the other side are Callisto and Ganymede.
The disc of the planet is so much brighter than the moon themselves that its next to impossible to take a picture of both together. The above exposure lasted a few seconds, while the exposure below was a fraction of a second. This short exposure makes it so we can’t see the moons, but we can see details on the ‘surface’ of Jupiter, namely tops of cloud bands. Note that there is only one equatorial cloud band (there were two for the past several decades).