Exploding Glass: Prince Rupert’s Drop

As anyone who has worked with glass knows, the material is fascinating. Glass is fragile, yet it can be extraordinarily strong. This is a seeming contradiction, but one that makes sense if you start to understand what makes glass crack.

Via Phil at Bad Astronomy, a truly awesome video on Prince Rupert’s Drop, a simple construct of glass that exhibits the strength and weakness of glass in a very visual way.

Science is cool!

Comet C/2011 L4 PanSTARRS

Well past perihelion comet C/2011 L4 continues to put on an impressive show. Amateur sky-watchers have been enjoying the impressive anti-tail reaching out a few degrees from the coma. True, you may need a telescope or at least good binoculars to see the comet. It may be dimming, but still worth the effort to observe.

Comet C/2011 L4 PanSTARRS
Comet C/2011 L4 PanSTARRS, 10x4min with TV-76 and Canon 60D @ISO2000

The iOptron ZEQ25

I had been looking to acquire another astrophoto toy. The desire is for a small, portable astrophoto setup. Yes, I am aware that the words “portable” and “astrophoto” do not really belong in the same sentence, all things are relative.

Thus I have decided on the new iOptron ZEQ25. It is a new design, with some radical differences from the more traditional German equatorial mounts.

The mount is pretty small, a mere 10 pounds of steel and aluminum. Compact enough to be packed into a suitcase for air travel. Performance sufficient to do wide field astrophotography with focal lengths up to 1000mm and a DLSR camera. Perfect for use with either my TV-76 or AT6RC. Unlike my old Losmady G-11 it features a modern GOTO system and can be run from the computer.

AT6RC & ZEQ25
AT6RC atop an iOptron ZEQ25 mount, note the additional counterweight necessary
The chatter over at Cloudy Nights was promising. A few early production mounts were in the hands of some stateside amateurs, and they have been posting their impressions and images. I was particularly impressed by the measurements of periodic error with results around two arc seconds. This was a small mount that could very easily be a good astrophoto option.

I ordered the mount from the good folks at OPT. It was not yet listed in the website catalog, but a phone call confirmed they were expecting delivery of three mounts shortly. I put down my deposit. A week later I had confirmation that the mount had been received and was ready for shipment to Hawaiʻi as promised.

Continue reading “The iOptron ZEQ25”

Mercury, Venus and Jupiter

This evening will see a line of bright planets in the sunset. Easiest to spot will be the brilliant Venus, shining at -4 magnitude and 15° above the setting Sun. 4°30′ below Venus will be Jupiter, quite low in the sunset, but bright enough to spot at -2 magnitude. 4°16′ above Venus will be Mercury, notably dimmer at -0.2 magnitude. The three will form an almost perfect line of bright objects in the glow of sunset, it should be a nice sight.

Three Hours on Two Tanks

I have had a few dives over 90 minutes, an hour and a half, on a standard 80 cubic foot aluminum tank. This time I managed two back to back dives totaling nearly three hours on two tanks. Not bad for air consumption! Admittedly I was moving slow, doing photography, on the other hand neither dive was all that shallow, averaging 30ft with deeper excursions.

Leaving Honokohau Harbor for a day of diving the Kona Coast
It was another day of diving off the Aqua Safari with the usual crew. Dennis, Sky, Pete and myself headed north from Honokohau for Kua Bay.

Kua Bay is the last public day use mooring north of Kona for a long distance, the next buoys are at Anemoʻohalu Bay, almost 10 miles further north. The mooring is adjacent to the popular Maniniʻowali Beach, a beautiful crescent of sand that is well loved and heavily used. A prominent finger of coral juts out from the shore north of the beach, creating a nice 20ft wall to explore.

I spent the entire dive poking along this wall, looking for small invertebrates. I was rewarded by an assortment of nudis and flatworms. Most were species I had seen before. One flatworm was something different, a species I am still trying to identify.

Dive Profile for Kua Bay
Dive Profile for Kua Bay on 26March 2013
For the second dive we headed north. There may be no further official day-use public moorings, but there are two large moorings just offshore the now closed Kona Village Resort. We tied up to the outer of these two moorings to see what we could find. The mooring is sited just outside of a coral shelf. While the mooring sits in 35ft of water, the shelf just inshore rises to about 15ft. Further out it appears the coral drops to a large sand flat, this we did not explore, spending the entire dive working the shallower wall of coral.

White Tip Shark
A white tipped reef shark (Triaenodon obesus) under a ledge in front of Old Kona Village
About 70 minutes into the dive I figured it was time for Pete to show up. I had not seen any sign of him for quite a while, he should be by any time now… He has had a habit of coming right over the top of me and trying to surprise me, it works with Mark, I think he is frustrated with my lack of reaction. Pete is right on time.

I signal to him, making a shark symbol, a flat hand held sideways to the forehead, that gets his attention. I lead him under a ledge a few feet away, where there is indeed a white tip shark hanging out. When we surface a few minutes later he sums up the encounter… “That is the biggest white tip I have ever seen!” Yeah, it was pretty big. Living up to the scientific name as well, Triaenodon obesus, a well fed shark, a little fat even.

After washing up the boat we head into Bite Me for dinner and to talk story. We thumb though the photos of the day reviewing all we had seen. It was an excellent day diving. The water conditions were notably better than a month ago. Summer is arriving, the swell settling down, bringing clearer water conditions. Looking forward to a summer of more diving!

Downpour

It looks like it may clear. There should be a few dark hours before moonrise. Maybe I can get the new astrophoto rig out and get everything working properly.

<Commence tropical downpour>

Nothing like two tenths of an inch of rain in half an hour to put a damper on astronomical plans.

Maybe it will clear later.

Scope and Rain
A tropical downpour ends plans to use the ‘scope.

Asteroid 2008 QE2 Ephemeris

Planning to make a go at photographing asteroid 2008 QE2 as it passes the Earth. Before I can do that a little planning is in order. Minor questions… Is it above the horizon near close approach, in my nighttime sky? It turns out this object will be available for observation.

The table below is a precision ephemeris generated by the NASA HORIZONS web interface for Mauna Kea on the island of Hawai’i. Listed are celestial coordinates, time, local elevation and azimuth, magnitude and distance. The marks after the time column indicate daylight (*), twilight (A) and moonlight (M).

From the data it is clear that the evening of May 30th (May 31st UT) allows observation from Hawai’i, at an elevation of ~46° a few hours after dark. Nicely placed and nicely timed for observation. Close approach is actually the next day, but the difference is minor. The next evening allows a second chance at the observation while the asteroid is still close.