Astro Images | Ring Nebulae

Browsing the Hubble Legacy Archive, I was intrigued by a small ring shaped nebula NGC 6369. It is also known as the Little Ghost. Discovered by 18th century astronomer Sir William Herschel, it lies over 2000 lt-yrs away in the constellation Ophiucus. The sun-like star at the center explosively blasted away its outer layers creating the ring of glowing gases. The star radiates strongly in ultraviolet causing the glow of the nebula. The blast also reduced the star to a white dwarf. For this color image, I combined three blue, green, and red filtered grey-scale Hubble images. The colors illustrate the presence of ionized oxygen, hydrogen, and nitrogen atoms.

NGC6369 | Hubble Legacy Archive | My Version

Fellow amateur astronomer Roger captured an image of his own recently of a different ring-shaped nebula NGC 7293 in his southern hemisphere sky. It is published here in his blog Cosmic Focus.

Astronomy fans are likely familiar with Messier 57 high in the summer sky of the northern hemisphere. It is another fine example of a ring nebula. Follow the link for a beautiful image and description.

Galilean Moon Events | 15 Aug 2021

The four largest moons of Jupiter are Io, Europa, Ganymede, and Callisto. First seen by Galileo Galilei in December 1609 or January 1610, he described them as satellites in orbit of Jupiter in March 1610. They are easily seen near the planet using a simple telescope or a steadied pair of binoculars. They are currently well placed with Jupiter in the evening sky to the southeast soon after sunset.

Imagine being high above Jupiter looking down at the planet and the four moons. Desktop planetarium software is very helpful here. In this view, Jupiter is centered. The Sun is far to the left off-screen. The moons are labeled in each of their orbits. The fastest is Io closest to Jupiter. Callisto is the slowest. Three of the moon have shadow lines drawn in orange. Play the video and watch their movements. The shadows cast by each of those three moons are intercepted by Jupiter. The software speeded up the rate many times.

What would this event look like for viewers on Earth? Earth would be located far off-screen to the left toward the Sun. Could we see the shadows cast by the moons upon the cloud tops of Jupiter? Again, software can simulate the view accurately. The answer is yes. Earthlings with powerful amateur telescopes are capable of seeing the shadows.

Play the video and watch for several things in this simulation. The first is Callisto casting its shadow on Jupiter. Over the course of several hours, it moves across the entire face of the planet. Next, Ganymede and Europa approach from the left. At 24 sec in the video, both of their shadows are cast. Also, Callisto’s shadow moves off the planet and the moon Io disappears into the shadow of Jupiter just off the right limb of the planet.

Watch at the 30 sec time how Europa is occulted by Ganymede. Both shadows are still visible but they become one briefly at the 32 sec mark. Finally, at 38 sec, both moons and their shadows are off to the right. Did you notice how Io emerged to the left of Jupiter in the distance? You might need to view both of these videos a few times.

On 15 August 2021, the moons were actually positioned as in my simulation above for viewers in the western Pacific region. Christopher Go of Cebu City, Philippines, captured images that night. He was fortunate to enjoy clear sky conditions for the duration of these events. His images are posted on his site. Scroll down his page until you reach August 15, 2021. The Astronomy Picture of the Day APOD highlighted his work.

Mississippi River Lock & Dam 15

In 2016, we traveled to Scotland. A highlight of our trip was the week-long barge journey from Inverness to Banavie. It followed the route of the Caledonian Canal allowing us to traverse Lochs Dochfour, Ness, Lochy, and Oich from the North Sea to the Atlantic side of Scotland. The canal was finished in 1822. A fascinating part of the canal is the system of 29 locks used to raise and lower boats. The highest elevation reached is 106 ft above sea level. Our post is here about the lock system. Pictured below is one of the sets of lock gates viewed with Google Maps. The water level in the upper right is higher than at the lower left.

Last week, my friend David and I traveled to the Mississippi River at the Quad Cities to do a boat tour of Lock & Dam 15 conducted by two engineers with the U.S. Army Corps of Engineers. They explained much of the history of the river and early attempts to navigate boats through this region. They also described the maintenance of the dam and locks to further their useful life. They also discussed some of the history of the Rock Island Arsenal as we passed by.

The multiple gates of the dam are on the left in the next image. They control the river flow from upper right to lower left. There are two locks for river traffic just right of center. Our tour boat passed through the smaller of the two locks. Large tugboats and their barges pass through the larger lock.

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