Andrew

What can go wrong?

I mentioned in another recent post that astrophotography is an art of details. Dozens of little issues must be dealt with, failure to properly address even one item, and hours of work can be lost. Each technical issue must be understood, and a solution found through technique and experience.

The saving grace of modern astrophotography is that once all the equipment has been set up and the details under control, the process becomes automatic. The computer, telescope mount, and camera operating for long periods of time, often hours, with no human intervention. One of the critical functions to long exposure photography is an autoguider, a small, automated secondary camera that keeps the telescope and mount pointed at exactly the same point in the sky for the entire exposure.

Guiding Error — An exposure of the Christmas Tree Cluster is guided into oblivion when the ST-4 autoguider loses the star

Last Sunday all was going well, several hours of exposures looked pretty good, at least on the little LCD display of the camera. The astrophoto gear had setup smoothly, all systems checked out and running well in just a few minutes after rolling the rig out of the garage. Mental checklist complete I hit the button to start exposures and left the gear to do it’s thing.

The first hint of trouble was the display on the autoguider. I did not see this until I went to stop the series of exposures I had hoped was complete. The guider was displaying large guide errors each cycle, where I should see zeros, or at least small numbers, it had E’s, a bad sign with the venerable ST-4 autoguider.

Hoping for the best, but fearing the worst, I rolled the ‘scope back into the garage and setup the camera to take calibration frames. I would discover the truth later, after I got a few hours of sleep.

When I downloaded the memory card the extent of the problem becomes apparent. Much of the last sequence of photos is ruined. The guider clearly lost the star somewhere into the third exposure, reason unknown. What resulted was twelve exposures with ziz-zag star trails across them, well over an hour and a half of wasted exposure time.

All of the evening’s early exposures were fine, only the last sequence was ruined. Thus, the evening was not a total loss, and I do have some new material to process. Now to figure out what went wrong with the autoguider, probably just some small detail I missed.

A Beam of Yellow to Pierce the Sky

Yellow light, specifically light at 589nm, the yellow glow of excited neutral sodium. A color of light familiar to anyone who has stood under the soft glow of low pressure sodium streetlights. A laser shining at 589nm, aimed high into the atmosphere, will encounter a layer of sodium atoms at an altitude of 90km (60miles). When the yellow light strikes this sodium it will excite the atoms and cause them to glow, creating a dot of light, an artificial ‘star’ in the sky.

Laser Optics — A sodium yellow laser propagating through the optics of the Beam Transfer Optical Bench

An artificial star, a useful thing if you want to analyze the distortion caused by the atmosphere. If you can understand these distortions you can use the information to correct the images of an instrument looking though the atmosphere, creating sharp views of stars and galaxies, views vastly better than were possible before the advent of adaptive optics. Such system are now routinely used on large telescopes across the globe to allow a clear view of the universe we live in.

First laser Light — The Keck 1 Laser piercing the sky for the first time on 28 Jan 2010

Adaptive optics systems are amazingly complex instruments. Hundreds of filters, lenses, mirrors and other optical surfaces interact with dozens of motorized stages and half a dozen cameras. Controlling the system are a horde of computers, some of which are specialized machines with impressive processing power. Everything must work in concert, the failure of one element can bring the whole system down.

A laser is not necessary for an operating AO system, but without it there is 70% of the sky that can not be observed, making a laser highly desirable. While the K2 AO laser has been operating for several years, Keck Observatory has never had a laser on the Keck 1 telescope.

Whitemouth

Zodiacal Light

A strange glow visible long after sunset, or well before dawn, along the path of the Sun in the sky. Called the “False Dawn” by Muhammad in Islamic texts and by other classical sources, this glow is often confused with the light of dawn, or simply overlooked by many.

Once thought to be the extended atmosphere of the Sun, the zodiacal light was recognized as something interesting by early scientists. The real reason for the glow was not understood until described by Nicolas Fatio de Duillier in 1684.

The answer is simply dust.

Space is not only very big and mostly empty, it can also be dirty. Dust from comets, dust from asteroid collisions, dust floating in orbit about the Sun, reflecting sunlight and glowing across the sky. Because this dust lies in the plane of the solar system the glow is visible as a band along the ecliptic and through the constellations of the zodiac. The dust is thickest, and the glow brightest nearer the Sun, thus the glowing dust is best seen when the Sun is just out of sight, after dusk, or before dawn. The light is simply reflected light. Looking at the spectrum of the zodiacal light shows it to be sunlight, with the same spectral features.

The zodiacal light can be quite bright, clearly visible to any who look in the hour after dusk, or before dawn. It can be bright enough to be a nuisance to amateur astronomers attempting to view through their telescopes. At the same time it is a sign of clear dark skies, as it is otherwise hidden by the glow of artificial light. The slightest amount of moonlight or light pollution and this glow disappears from sight.

The effect can be seen completely across the sky, along the ecliptic, as a very faint glowing band when viewed from the darkest of places. Directly opposite the Sun in the sky is a brighter spot in the glow, the gegenschein or counterglow. A form of glory, the dust reflects sunlight back in the direction it came.

The zodiacal band and the gegenschein are both visible from Mauna Kea on a dark night. From this dark place the most subtle of astronomical spectacles can be appreciated.

Lunar Halo

A lunar halo may be quite pretty, but along with pretty sunsets, it indicates lousy sky conditions for astronomy.

In this case a high layer of thin cirrus, consisting of small ice crystals, cover the sky. The crystal shape is just right to bend the light at a specific angle, creating a halo 22° from the light source. A faint hint of color can be seen at the inner edge of the halo.

Meteor Fireballs

Thanks to all of those folks who posted comments about meteor fireballs. As I mentioned, these sort of events are not all that uncommon, and occur regularly across the globe. What is unusual is good photos of the event. This did happen this week, a photographer had a good camera at the ready when a similar fireball came in over Groningen, Netherlands on October 13th. Great photos of an event much like the one we saw last week over Hualālai. Check out his page for the full set of photos including the final breakup, the website is in Dutch, but a Google translation will let you follow the description.

Mikaelyan Meteor — A meteor breaking up over Groningen, Netherlands, 18:57, 13 Oct 2009, photo by Author AndrewPosted on October 16, 2009April 28, 2013Categories Meteor ShowersTags fireball, meteorLeave a comment on Meteor Fireballs

Fireball Over Hualālai Update

Looks like several folks saw this meteor come in, including the entire evening crowd at the VIS. Another report from Kali on Maui emphasizes just how bright it was.

Larry O’Brian reports from the VIS…

The highlight of the evening was unquestionably a spectacular fireball that burned brilliant green, slow- moving, threw off at least one fragment, the whole enchilada. No sound, other than thirty people shouting ‘wow!’ I first caught it around, say, Aquila heading towards Ophiuchus, but people were already calling out about it.

Between Larry’s excellent report and my own sighting I can place this meteor coming in steeply somewhere over or just south of Hualālai. From around the summit to out to sea beyond Kealakekua, much closer than I would have thought. Given the breakup and low altitude the proximity implies there could have been pieces reaching the ground. Anyone in South Kona report something hitting their roof?

Any readers want to join me search an entire 9,000ft volcano for meteor fragments? Spotting dark fusion crusted meteors on top of fresh black a’a basalt ought to be easy… Not!!!

Fireball Over Hualalai

Nice meteor fireball just a few minutes ago. Just as Deb and I were driving down Waikoloa Road, about 8:06pm, due south over Hualalai. It lit up the landscape a bit, very bright, with fragments flying off as it came in.

Given the time, mid-evening with dinner events and Iron-Man festivities underway, I suspect more than a few people along the coast noticed this one.

Green Laser Trouble

Sounds like someone acting very foolishly has pointed a green laser at aircraft around the Hilo airport. Thanks to Baron for noting the HPD press release on the issue. I wonder if there is someone out there who is unaware that aiming a laser at an aircraft is a violation of federal law.

Lasers at the VIS — Green lasers in use at the Mauna Kea VIS nightly observing with the Milky Way high overhead

Green lasers have been in the news quite a bit over recent years, ever since they became inexpensive enough that people buy them on a whim. Lasers in the under 100mW range used to cost hundreds of dollars, can now be ordered on-line for less than fifty dollars. There have been multiple incidents of these lasers pointed at commercial and law enforcement aircraft. Fortunately the usual result is simply distraction for the pilot and no accidents have been reported from laser interference with flight operations.

These lasers are also immensely useful. At the VIS and other local star parties we use green lasers to point out the constellations and to educate our visitors about the sky. There is nothing like being able to point out a specific star, nebula or galaxy directly, you can instantly connect an entire audience with the sky without the usual confusion. Friday night it was a green laser that served as a link to the stars when I used it on the patio of the Mauna Kea VIS.

I use a laser under 30mW, bright enough to be seen by a large crowd, as well as being visible with a bright Moon in the sky, but with a low enough power to be reasonably safe. Above about 50mW these laser pointers become much more dangerous as the laser can inflict injury to the eye faster than you can blink and turn away. Fortunately there is almost no air traffic over Mauna Kea making this a place where you can use the lasers with little worry. Another personal rule I follow is to never let kids handle this laser, even though they always clamor to see this bright wonder of technology.

I can only hope this issue does not attract the attention of our reactionary county council, they have a tendency to ban anything that even seems dangerous. This would be another classic case of one stupid person creating problems for those of us who use a technology responsibly.

A Great Night at the VIS

Last night was the sort of evening we love, and the reason we volunteer at the Mauna Kea Visitor Information Station. One of those nights where the stars seem close enough to touch, we bring them within reach of those who came to the mountain to learn about the universe.

MKVIS at Night — The Mauna Kea VIS at night with a crowd at the telescopes

Conditions were near perfect, a dark, clear sky with no Moon, it would rise later. Not only was it dark, but the air was steady, allowing nice high magnification views of Jupiter and other objects. The air was still, it was cold, but without the wind that can make conditions miserable at 9,200ft. The result was a beautiful night that everyone cold enjoy to the fullest.

Joining us were visitors from around the world, I met people speaking German, Spanish and Czech, a British family living in Japan, and more. About fifty people were to be found on the patio when I did the evening star talk. Not only did they come, but they came with curious minds and a will to learn. The questions came from all sides, fast and furious, a constant stream of information.

With such beautiful sights in the telescope to see, the questions just come naturally. I used a C-14 on the Astro-Physics mount to jump from object to object, the Swan Nebula, the globular cluster of M22, the Andromeda Galaxy, the Wild Duck Cluster, the Ring Nebula, the Dumbell Nebula, Alberio. Everything looked so nice that even as jaded observer, I found myself lingering at the eyepiece to enjoy the view.

The evening was a series of personal conversations with one group or family. I would try to use little vignettes to put the knowledge in context, the shape and size of our galaxy, or the story of star birth and death. Trying to convey, in a few minutes, a little glimpse of a bigger picture and not just a mess of gee-whiz information. Sometimes this works, and you are rewarded with a moment of connection, where your audience suddenly understands.

That is what we come to the mountain for.