Tom

Jul 042017
 

After wrapping up the last JunoCam series on the 1st I noticed that the Moon was in a good position to get some terminator images. The Moon’s terminator is the line dividing the daytime side of the Moon from the nighttime side. So, at the terminator, the Sun appears to be rising. This puts the light from the Sun hitting that area of the Moon at a very low angle. At that low angle, mountains and crater walls cast long shadows providing a noticeable 3D effect.

The image below is a heavily cratered area of the south central section of the Moon. The large, deeply shadowed crater towards the top center of the image is crater Maginus. A notch in the crater wall allows a beam of sunlight to spear into the shadows illuminating an area of the crater floor.

Also visible toward the bottom, again deep in shadows, is a crater rim just catching the rising Sun. In fact, the illuminated rim looks like a sickle with the pointed end angled to the right. This is the rim of crater Hell. No, not that Hell. The crater is named for the Hungarian astronomer and Jesuit priest Maximilian Hell. He was appointed director of the Vienna Observatory in 1756.
 

Map generated with Virtual Moon Atlas

The next image is from a little farther north. The dark area to the lower left is the southern portion of the Sea of Tranquility. Of note in this image are the two rilles toward the bottom center and right. A rille is a long narrow depression that looks like a channel. The horizontal rille at center bottom is Rima Ariadaeus. Rima is the latin name for a rille. Rima Ariadaeus is over 180 miles long and was formed when the surface of the Moon pulled apart at parallel faults and the section of crust between sank.

The other rille, Rima Hyginus, is split into two sections by the crater Hyginus. However, this crater is not an impact crater. It is a volcanic caldera. So, the associated rille is thought to be formed by ancient collapsed lava tubes. It is most visible in the section to the right of the crater. Upon close examination it appears the roof of the tube collapsed in a series of connected craters.

Map generated with Virtual Moon Atlas

Also visible in the above image are the landing sites for Apollo 11 and 16. Apollo 11 is in the southern part of The Sea of Tranquility along with the three craters named in honor of the crew members. The Apollo 16 landing site is further south just to the right of the small but prominent crater Kant which is right of the largest crater Theophilus.

 Posted by at 16:18
Jul 032017
 

With my treeline obscuring Jupiter so quickly after sunset, I will reconfigure the PTO back to deep sky imaging tomorrow, the 2nd of July. So, this is the last JunoCam image until next year.
 

By mid March, Jupiter will become a morning target and rise above my eastern treeline by 0200. The PTO will resume supporting the JunoCam project then. How long the project lasts is all up to Jupiter’s radiation and NASA. The intense radiation is expected to eventually degrade each of the scientific instruments despite the spacecraft’s titanium shielding. If the instruments are no longer functional the Juno mission will end in July 2018. If some are still working it will be up to NASA to decide if additional funding is warranted to extend the mission.

 Posted by at 16:25
Jun 272017
 

The Earth’s orbit is taking us further and further from Jupiter. This means that the time I get to image Jupiter gets less and less as the Earth starts to round the Sun. Less time to image results in fewer candidate video streams.

Earlier in May it was dark before Jupiter cleared my eastern treeline and, once it was dark, I was able to get as many as 57 attempts. On the 22nd, I was only able to get 9 attempts before Jupiter hit the western treeline and after processing, only 1 of the 9 met the criteria for submission to NASA’s JunoCam site.

 Posted by at 17:05
Jun 192017
 

The sky last night was one of the darkest (and clearest) we have had in quite a few weeks. I was able to get a short JunoCam series before Jupiter hit my western tree line.
 

Ideally, if you want to image for an hour, the best time as far as the atmosphere is concerned, is the half-hour before the target gets to the zenith and the half-hour after it passes the zenith. But right now Jupiter gets only 55° high and is well past the meridian before the sky gets dark. That means the planet starts with less than optimal airmass and as the night progresses descends into ever increasing airmass.
 

Airmass is the length of the pathway through the atmosphere that the photons from the object you are looking at have to pass. The path length above the zenith is about 100 km and the path length along the horizon is about 1020 km. By definition, airmass is 1.0 for an object directly on the observer’s zenith. The lower in the sky, the higher the airmass gets. The longer atmospheric path means more distortion, absorption and refraction.

Close to the horizon, the object doesn’t look like it really does (distortion), isn’t as bright as it really is (absorption) and isn’t where it looks like it is (refraction).

 Posted by at 20:11
Jun 142017
 

Yesterday’s rain eased off and the clouds cleared around 2300. That gave me an opportunity to open up the dome and get a short series of Saturn images before the clouds closed back in. The atmosphere was fairly steady and the images showed it. Jupiter had already set below my western tree line so I was unable to get any additional images of Jupiter for NASA’s JunoCam project.
 

I was not the only one taking advantage of the clear sky. The other party posed for a selfie on the PTO’s all sky camera.

 Posted by at 20:06