Tag Archives: Tycho

Rayed craters make tonight’s full moon spectacular

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At full moon, the sun, Earth and moon are nearly in a straight line. An observer on Earth (blue) sees sunlight illuminating the moon's face from directly behind. Illustration: Bob King

Tonight’s the Full Hunter’s Moon, so be sure to spend a bit of time polishing up your moon tan with a stroll outdoors. A full moon is always directly opposite the sun in the sky and rises around sunset.  For Duluth, Minn., moonrise is at 5:57 p.m. or 32 minutes before sunset. To find moonrise time for your location, click HERE and key in your city, state or country. Be sure to add one hour to the times shown to convert to Daylight Saving Time.

During other lunar phases, we only see a part of the moon because of the varying angles between Earth, sun and moon. At full phase, all three orbs are lined up. The sun shines over the Earth’s “shoulder” hitting the moon’s face square on and lighting up one whole side of the lunar globe. Just as a light shining directly in your face hides the shadows cast by your nose, cheekbones and yes, your wrinkles, so the sun shining in the moon’s face hides all shadow detail. The result: a flat, pasty, two-dimensional-looking moon.

Without shadows to reveal lunar contours and the craggy details of crater walls and mountain peaks, most amateur astronomers don’t bother looking at the full moon. Besides, it’s about the only time we can get some rest, right? But I’m here to tell you that I’ve been smitten the past few years by the spectacle of all the rayed craters that come into their own when the moon hits your eye like a big pizza pie.

The four biggest and easiest to see rayed craters are visible in all their glory during tonight's full moon. Credit: Frank Barrett

Rayed craters are craters surrounded by halos of impact debris that were excavated when meteorites and asteroids struck the moon long ago. Pulverized rocks from those impacts shot out like fountains miles above the moon’s surface before falling back and blanketing the vicinity of the newly-formed craters. Some of the falling rocks were large enough to create secondary impact craters which in turn exposed more fresh crustal materials. That’s why the rays are bright compared to much of the lunar surface – the impacts that made them happened relatively recently.

Recent in astronomy is always a dubious term. In the case of rayed craters, the impacts occurred in the past billion years compared to 3-4 billion for the majority of the craters we see. Over time, exposed material on the moon’s surface darkens due to a constant pounding by subatomic particles streaming from the sun called the solar wind.

The youngest and most magnificent rayed crater is Tycho located near the “bottom” or south end of the moon. It’s only 109 million years and its rays stretch across many hundreds of miles. Tycho and the trio of Copernicus, Kepler and Aristarchus comprise the best and the biggest of the rayed craters. All can be seen with the naked eye though any pair of binoculars will make the task much easier. While shadow detail may be compromised at full moon, rays shine their brightest then.

See all those tiny white spots? Through a telescope the moon offers up dozens more rayed craters. They speckle the disk like glitter - a sight to see! Photo: Bob King

If you own a telescope, I’m going to ask you to take the next step and examine the moon at low to medium magnification tonight. Yes, you’ll feel like you’re going blind in one eye but rest assured, it’ll be worth it. Splayed across the disk – especially the central area – are many dozens of additional rayed craters. There’s nothing like the sight of them. Centered on their respective, freshly-punched craters, I’m reminded of brilliant beacons, tiny explosions, stars and flares. What will you see? May your sky be clear tonight.

A Full Buck Moon and stroke-of-midnight asteroid encounter

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NASA's Dawn spacecraft obtained this image of the 329-mile diameter asteroid Vesta with its framing camera on July 9, 2011. Image credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA

Look how nicely the asteroid Vesta is coming into focus in this picture taken by the Dawn spacecraft on July 9 from a distance of 26,000 miles. In addition to craters, numerous troughs are visible around the raised ‘bump’ below center. It’s only an educated guess, but this area looks like the site of the giant impact that excavated a 290-mile diameter crater centered near the asteroid’s south pole. Unfortunately, no addition information was included with the caption.

Vesta’s gravity is expected to ‘capture’ Dawn around midnight CDT Friday night. At that time the two will be 9,900 miles apart and 188 million miles from Earth. Once in orbit, the spacecraft will study and photograph the asteroid for one year.

The full moon rides low in Sagittarius tonight. If you extend a line some 3 'fists' to its upper left, you'll meet up with Altair. From there, you can find the Summer Triangle. Created with Stellarium

Closer to home, tonight and tomorrow night mark the time of July’s Full Buck Moon. For observers in the Western Hemisphere the moon will look a bit fuller tonight than tomorrow night, because the moment of full phase happens at 1:39 a.m. CDT tomorrow morning. By Friday night, the moon will be 3/4 day past full.

The Buck Moon is named for buck deer, which start to grow their velvety horns this time of year. You might also hear it referred to as the Thunder Moon, a fitting seasonal name if there every was. The moon will rise around sunset both evenings in the constellation Sagittarius.

By 10 ‘o clock, it’s up high enough in the southeastern sky to enjoy a moonlit walk. As you’re strolling along, you’ll notice the moon is divided into two main types of landscapes: the bright lunar highlands or original crust of the moon, that formed some 4.5 billion years ago, and the darker maria (MAH-ree-uh) or lunar seas. These lava-flooded basins are some 500 million to a billion years younger.

The crust of the moon solidified some 4.5 billion years ago and is covered with craters from the impact of meteorites and small asteroids. The darker areas or seas formed more more recently when lava filled large basins left by asteroid impacts.

Near the bottom or south edge of the moon is a brighter spot that can just be detected with the naked eye. That’s the 54-mile diameter Tycho, a relatively fresh crater surrounded by rays of impact debris that reflect brilliantly around the time of full moon. In Tycho’s center is a pointy mountain peak that stands about a 1.2 miles above the crater’s floor. Tycho’s features are unusually sharp and fresh, because the crater’s only about 110 million years old. Compare that to the several billion year age of the average lunar crater.

Tycho crater's central peak complex, shown here, is about 9.3 miles wide, left to right. A curious boulder is just visible as a white spot near the pinnacle. Credit: NASA Goddard/ASU

Recently, the Lunar Reconnaissance Orbiter (LRO) took a magnificent closeup picture of the peak that is a MUST SEE. While the image hints at the detail recorded by the probe, please click on it to see the high resolution version. The scene is so rugged and real it will really open up your eyes.

To see more photos, including closeups of the big boulder sitting in the saddle between peaks, click HERE.

Take the plunge into that burnin’ ring of fire

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Individual dew drops line a blade of grass this morning. Photo: Bob King

Yesterday on a walk in Hawk Ridge Nature Reserve near my home, a flock of migrating nighthawks blew by headed south. I identified them right away by their white wing patches. Birds on the move, cool mornings lavish with dew. I like these hints of fall. Through the telescope last night, the nearly 12-day-old moon served as an illuminated stage for the passage of yet more birds. Over a period of five minutes, I saw some a dozen silhouetted avians zip across the cratered landscape on their way outta here.

Now through September is an ideal time to point your telescope at the waxing moon — especially around full phase — to watch birds migrate at night. We don’t think about it much, but many birds are busy migrating while you and I are out like a light. Hummingbirds, warblers and others not only avoid the heat of day by doing so but are less likely to get nailed by a predator under cover of darkness. To watch the show, all you need is a small telescope and a big moon. Plunk in your low power eyepiece and just wait. I saw my first bird within a minute. They fly by quickly, but since I’m no bird expert, I couldn’t identify the different species. Craters are my forte.

Numerous white rings, splashy bright patches and ray systems are best visible around the time of full moon. Credit: Frank Barrett

Some amateur astronomers scorn gibbous and full moons as worthy of study because they’re too bright, and the landscape is washed out due to the sun shining almost directly above the moon’s surface. When the sun shines from the side, as it does near sunset and sunrise both here and on the moon, everything casts a shadow and shows minute detail. Every bump, wrinkle and hair on a person’s face stands out in glaring detail. But shine a light directly at a person’s face – equivalent to the sun shining squarely over the full or nearly full moon – and shadows and those disturbing wrinkles disappear, lost in a flood of light.

A full moon offers no sense of depth or relief, but does reveal details otherwise invisible at other lunar phases. That includes many small craters which hardly anyone notices during lesser phases, but which are transformed into brilliant rings during the equivalent of lunar high noon.  Last night I lost count of how many of these “hot rings” I saw through the telescope at low power. They’re so brilliant they resemble white flares or fiery white-hot rings of lava. Johnny Cash’s “Ring of Fire” comes to mind.

What you’re seeing is high-angle sunlight reflected off fresher rocks and soils on crater rims and floors or from the tendrils of long rays (splashed rock) surrounding fresher craters. The rays and lighter soils truly shine around the time of full moon. Once you get into seeing these strange lunar lily pads, you’ll be surprised at how alien they look compared to the more familiar peaks and crater holes seen to advantage at other phases.

Proclus crater photographed by astronauts aboard Apollo 15. Credit: NASA

I was particularly struck by the fiery ring of Proclus crater and its peculiar off-center system of rays. Proclus, at 18 miles in diameter, is a young lunar crater, and the brilliance of its rim is clearly the result of fresh rock exposed by impact that has yet to darken under the influence of solar radiation. It contrasts beautifully with the older, surrounding moonscape called Palus Somni or the Marsh of Sleep. The weird forked appearance of the rays suggests that the asteroid that created Proclus struck the moon at an oblique angle.

Several of the brightest craters and their systems of rays (strings of fresh secondary craters formed by rock ejected during the main crater's creation) around the time of full moon include Tycho and its rays, Aristarchus and Proclus. Credit: Frank Barrett

Other brilliant craters and ray systems include Aristarchus (brightest crater on the moon) and Tycho, and there are many more. Like Proclus, they’re relatively fresh craters compared to most. With binoculars you can see all three of the aforementioned as bright spots, while any telescope will show their ring-like forms and feathery rays in far more detail. Between moon and birds, you may find yourself staying at the telescope side later than you thought tonight.