Observing Deep, Far Away, and Long Past
It is no surprise to experienced deep sky observers that locating and observing details of objects with magnitudes beyond 14 requires dark skies, visual acuity, and telescopes over 20 inches in aperture. With my ten-inch Dob, Herschel objects that are Magnitude 13 usually appear as faint fuzzy spots and observing detail requires averted vision or imagination or both. After completing the Messier list with my six-inch telescope and the Herschel 400 with my ten-inch telescope, I was looking for another challenge. I wanted to go deeper to observe objects with detail in the range above Magnitude 14. From my experience at various star parties, even the owners of much larger telescopes were not observing objects in the ranges I wanted to explore. My solution was to dive into CCD imaging, not with the intent of producing pretty pictures of bright objects, but as a tool to allow me to make detailed observations of faint objects and perhaps even discover a minor planet or supernova. With CCD imaging those with visual impairments or night blindness can observe objects they would be unable to see with a telescope, and image-stacking methods mean light pollution and moonlight are less of a problem.
After purchasing the required equipment and software and spending over a year to climb a steep learning curve, my spouse and I are making observations that I never thought possible. Our latest challenge has been to image the galaxy groups and clusters from a list published by the Astronomical League, The Galaxy Groups and Clusters Visual and CCD Observing Guide by Bob McGown and Miles Paul. The clusters and groups on the list contain as few as three galaxies or as many as 30. They are divided into 50 galaxy trios from The Atlas of Compact Galaxy Trios compiled by Miles Paul, 99 Hickson Compact Galaxy Groups, 50 additional galaxy groups (most located in the Virgo cluster), and 50 Abell clusters. Einstein’s Cross is included as a challenge object. To receive the Astromonical League’s Galaxy Clusters and Group Award one must observe 120 clusters, with 30 clusters (including each galaxy in the cluster) from each group. Either visual or CCD methods may be used to observe the clusters and member galaxies. When I first began observing galaxies a few years back, I saw them as individual objects. But as one goes deeper, further away and further back in time, single galaxies lose their individual identities and because of gravitational attraction are usually members of groups or clusters. Clusters can also group into super-clusters. Examples include those in Perseus, Coma Berenices, Virgo, and Corona Borealis. The universe is not uniform but is “lumpy” with clusters of galaxies from small, local groups to immense walls of galaxies.
Figure 1. Hickson cluster 96 taken at the Oregon Star Party 8/14/04. There are four galaxies: a. NGC 7674 mag. 13.5, b. NGC 7675 mag. 14.5, c. MCG +1-59-81 mag. 15.7, and d. PGC 1507 mag 16.6. NGC 7674 is a Sb spiral galaxy type showing two arms and NGC 7675 is a E0 elliptical galaxy type. MGC +1-59-81 is an E1 elliptical galaxy type. PGC 1507 is too faint to determine the type. The total integration time was 7.5 minutes. Apparent sizes of these galaxies are very small. Here the image field is less than 0.1 degrees.
One of the observation requirements of the award is to make an attempt to characterize each galaxy’s shape. Shape variation of individual galaxies within a cluster is complicated, but they can usually be placed into one of four structural types: elliptical galaxies, consisting of a nucleus, a central bulge, disc, and corona, ranging from spherical discs (E0) to elongated discs (E7); lenticular galaxies (SO) with a central disc but no spiral arms; spiral galaxies (Sa-Sd) with a nucleus and a thin or thick disc and a galactic halo that sometimes can take the form of arms; and barred spiral galaxies (SBa-SBd) with a barshaped nucleus across the spiral structure. Many clusters will have several types of galaxies ( Figure 1). Not all galaxy shapes fit the classic types as can be seen in the Hickson 93 cluster (Figure 2). In this cluster the nucleus of NGC 7549 has a curved shape and one arm seems to be missing.
Figure 2. Hickson cluster 93 taken at the Oregon Star Party 8/13/ 04. There are four galaxies in this cluster: a. NGC 7550 mag.12.6, b. NGC 7549 mag. 3.2, c. NGC 7547 mag 13.9, d. CGCG 454-15 mag. 15.3. NGC 7549 has a very distorted nucleus. The field of view is less 0.2 degrees. The image was the result of five stacked three-minute images.
Some clusters show clear interaction between galaxies similar to that observed in M51. For example, in the Hickson 92 cluster the nuclei of NGC 7318A and NGC 7318B are clearly interacting (Figure 3).
Figure 3.Hickson cluster 92 taken at the Oregon Star Party 8/13/ 04.Of the five galaxies in this cluster, NGC 7318 A and NGC 7318 B seem to have interaction: a. NGC 7320 mag.12.5, b. NGC 7318 B mag. 13.2, c. NGC 7319 mag. 13.3, d. NGC 7318 A mag. 13.6, and e. NGC 7317 mag. 14.0. The field of view of this cluster is less than 0.1 degrees. The image is made of five raw threeminute images that have been stacked and processed. The total integration time was 7.5 minutes.
It is often necessary to confirm a galaxy’s identification in a cluster. One way to do this is with direct comparison with Digital Sky Survey (DSS) images obtained from various sources on the Internet. This also allows comparison of our image results with those taken with telescope systems costing hundreds of thousands of dollars more. (Figures 4, 5). Yes there is a difference. Equipment: I purchased a Meade ten-inch LX200 GPS for the simple reason that the instrument provides both the OTA and GOTO mount in one package for a reasonable price. I have added upgrades to the basic telescope including a Milburn wedge, a 6.3 focal reducer, steel gears in the drives, and upgraded thrust bearings in the focus mechanism. Except for some minor problems initially, the telescope has performed as hoped. Our CCD camera is a Starlight Xpress MX 916, a very sensitive low noise camera designed for imaging deep sky objects.
Figure 4. A stacked image of a group of galaxies in Cetus from the Atlas of Compact Galaxy Trios, taken 10/14/04 at Sky View Acres near Goldendale, Washington: a. NGC 426 mag. 12.8, b. NGC 429 mag. 13.4, c. NGC 430 mag 12.5. Comparison of this image with the DSS image in Figure 5 confirms the identity of these objects.
Figure 5. A DSS image downloaded from the Internet of the same group of galaxies as those in Figure 4: a. NGC 426, b. NGC 429, c.NGC 430.
Telescope Control: We use Autostar II firmware for automatic alignment, focus control, and periodic error and backlash corrections in the drive system. Starry Night Pro software is used for synchronization and GOTO procedures. Star2000 interlaced guiding technology provides automatic guide corrections during imaging. Software: We use AstroArt 3.0 for camera control and image processing. Starry Night Pro is used for charting, telescope GOTO control and sync. Deep Sky 2000 is used for planning observation sessions. Cartes du Ciel produces detailed star charts for confirming an object’s identification and Live Sky links via Starry Night Pro provide DSS Internet images.
Procedure: Because the telescope and mount is equatorially mounted, all observation begins with polar alignment. With the LX200 the alignment location and timing is automated, but we still need to center Polaris using wedge adjustments. We also center selected alignment stars manually, and perform drift alignment to remove drift caused by errors in polar alignment. We center the telescope on a star in the range of Magnitude 7 – 9 using a 9 mm illuminated crosshair eyepiece, replace the eyepiece with the CCD camera, and focus with a Kendrick focus mask and fine adjustments controls on the Autostar II keypad. We use Starry Night Pro to locate and slew to objects. In some situations it is necessary to sync on a nearby star before slewing to an object. Test images confirm that the object is centered on the chip. We use AstroArt’s telescope command buttons to center an object. Then we select a guide star and start Star2000 guiding to track the object within one pixel, representing about 3 seconds of arc. We make a series of raw 180 second images, with the number of image frames depending on the sky conditions and the object brightness. The resulting images are stacked and calibrated with dark, flat, and bias frames using AstroArt.
Image processing means removing the background gradient and performing DDP (Digital Development Process). We can image 5-10 objects per night. Future Plans: We have just started to explore the capabilities of our equipment. Future plans include increasing image resolution by using high resolution binning methods, using imaging software for the detection of minor planets, and experimenting with filters to reduce light pollution and improve image detail. Automation of image acquiring procedures and remote control of telescope and CCD camera will also play a significant role. Amateur observers wishing to go deeper and far away with their observation programs might wish to consider CCD as an alternative to a larger telescope. The cost of CCD equipment continues to decline as the sensitivity and capability continues to increase. Cameras capable of deep sky imaging are now being marketed for less than $300. Could the era of the Big Dob be ending?
Reference: Galaxy Groups and Clusters : a Visual and CCD Observing Guide for the Advanced Amateur Astronomer, Bob McGown and Miles Paul (Astronomical League, 2003.)
Astrobiology: Mars News
I’ve almost lost track of what’s happening on Mars. We live in an unprecedented time for extraterrestrial exploration, with public access to most of the data and interpretation. Nevertheless, while the local weather was good, I was so absorbed by the world at my feet or just up the road, that I took little notice of the news from our neighboring planet. This fall at UW I’m on an oceanography tangent and miss most astronomy and astrobiology seminars. However I’d be there if anyone offered to review what’s emerged from the Mars missions, and I’ll eagerly enroll when a course on the subject is offered. (Paul Middents?)
In an attempt to catch up, I decided to compose a one-page summary and open the subject for comment. I’m sure no expert, but here goes. Hit me with your best shot (constructive/instructive criticism, that is).
l Maps are the tools and first fruits of exploration. Mars Global Surveyor (MGS), launched in November 1996, carried into stable orbit 250 miles above Mars a package of instruments that yielded data from which an extraordinary photo-montage has been constructed. A detailed topographic map of the entire planet was assembled by combining photos from its Mars Orbiter Camera (MOC) with data from its Mars Observer Laser Altimeter (MOLA). MOLA resolves features to 10 meters in height. The story of these instruments, and the people behind them, has been told very well in a book, published in 2002, by Oliver Morton, entitled Mapping Mars (available at Kitsap’s libraries).
The 50,000th image from NASA’s pair of Mars Exploration Rovers: it shows the camera’s calibration target,,with a glimpse past it to rocks and soil in the “Columbia Hills” ( NASA/JPL/Cornell)
A wall map drawn from the MOC-MOLA data, distributed with the February 2001 National Geographic, barely suggests the map’s fine detail. l MGS was succeeded by Mars Odyssey, launched in April 2001. It began producing useful data in Febuary 2002 and within a few months provided evidence of vast quantities of water (hydrogen atoms, at least) near the surface of Martian soil (40-70% ice by volume, compared to 30% for terrestrial permafrost) at mid-tohigh latitudes in both hemispheres. (Page 9, BPAA Newsletter July 2002, and NASA/JPL August 25th, Odyssey press release). Odyssey surveyed Mars for a full (23 Earth-month) year, and the mission was just extended through 2006 enabling it to look for climate change. Odyssey’s data, combined with MGS maps facilitated choice of significant landing sites for two amazing robots, which have gone on like Energizer Bunnies–nine months!
3-D Mesh Map represents the topography of Spirit’s location on sol 192.( NASA/ARC )
l Opportunity, although the second to arrive (January 24th), was the first to strike pay-dirt. It confirmed that the extensive flat region where it landed, Meridiani Planum, is covered with hematite, an iron mineral which commonly develops in aqueous environments. It spent two months examining layered sedimentary outcrops around the shallow Eagle Crater which appear to have been under water for quite awhile. Gray 1-2 mm diameter spherules, dubbed “Blueberries,” appear to be concretions like those that form terrestrially when hematite precipitates from mineral-laden water and coats sand grains. Significant amounts of the elements S, Cl and Br were found, as they are where salty brine has been evaporated; also a hydrated iron sulfate, jarosite, which forms only in acidic lake springs on Earth. Many of the Meridiani rocks contain small (<1 cm) linear cavities that could have formed when soft evaporite salt (e.g. CaSO4) crystals were leached or eroded from earlier deposits. Cross-bedding and ripple marks on several rocks support the interpretation that they accumulated in a salty body of water which flowed for substantial periods. Opportunity moved on (0.8 km in April) to explore Endurance, a large meteor crater. It is now traversing the inside rim. l Spirit landed on Jan. 4th in a less geologically-exciting environment at Gusev Crater.
It worked its way, examining numerous rock formations enroute, some 3.6 km to the “Columbia Hills,” where it recently encountered highly-altered soft rock (also containing elevated levels of S, Br & Cl), which appears to have been eroded by water. All this evidence of Mars’ aqueous history fosters hope that fossil signs of microscopic life (if there ever was any) may be found by future missions to the planet, while the water still under the surface bodes well for human exploration.
The Moon in the Shadow of the Earth, October 27, 2004 : An Eclipse Gallery
During a total eclipse the moon is in the darkest part of the earth’s shadow, the umbra. But it still reflects light. The earth’s atmosphere acts like a lens, and bends rays of sunlight into the umbra. The light the moon reflects during an eclipse is usually orange or red, even bloodred, because the lens of the atmosphere scatters blue wave-lengths, leaving the redder, longer wave lengths to travel to the moon. Conditions on earth, such as volcanic eruptions, can change the refractive properties of the atmospheric lens, and alter the color and brightness of a lunar eclipse.
Doug Tanaka/15xbinoculars and digital camera
George McCullough/Early Totality
Rik Shafer/digital camera and tripod
Don Willott/3X optical zoom
Doug Tanaka/Moon Over Puget Sound and Yellow Moon