The Official Publication of the Bucks-Mont Astronomical Association, Inc ________________________________________________________________________________________________________________________________________
VOL XV, NO 7 JULY 2000 Scott Petersen, Editor
© 2000 BMAA, Inc
- by Jay Ryan
When my wife Debbie and I lived in Washington DC, we became good friends with a couple from New Zealand, Richard and Lynn, who were staying in the States for a time. Richard and I were observing buddies and also made telescopes. We visited them after they returned home in December, 1991, and it was the astronomy vacation of a lifetime. *
It was a cold winter morning when we left, in early February 1992. That morning I went jogging early before sunrise, and saw Venus, properly on the right side of the orange sunrise glow. We left Baltimore Washington International Airport and on the flight out to LA, we passed over Meteor Crater in Arizona. It looked great from the air, about one degree across. Using hand angles to measure sizes and separations, I figured we were flying at about 25,000 feet.
Our flight departed LA after dark. The fully booked flight from LA to New Zealand took 12 hours, quite a long time to be in an airborne sardine can! We crossed the Equator while I slept. It was the first time I ever could sleep on a plane! The plane kept pace with the Earth's rotation while staying in the Earth's shadow, so it was dark for the whole flight. We were in the dark for a total of 16 hrs, which having always lived near 40 north, was the longest night I'd ever had.
We arrived in Auckland before dawn the next 'day'. I completely lost track of time, but it was the next sunrise I'd seen after that morning run. As the plane taxied down the runway after landing, I looked out the window and again saw Venus, but now it was to the left of the sunrise! It then hit me like a load of bricks -- wow, we really were in the Southern Hemisphere!
The first thing that struck me was the reversal of seasons between the hemispheres. I noticed in comparison that winter is not only cold, but a very still and quiet season. When we arrived "Down Under", summer was in full swing, very warm, and a very noisy and active season in comparison. It seem that you don't notice the changes as much over the course of the year since the seasons come on slowly, but when you're suddenly dislocated to the opposite season, all the little nuances become very apparent.
In New Zealand, I could never get my bearings for the time of day, and it took nearly a whole year for my clock to get completely back on track. It was kinda disorienting. The Sun appeared to move the wrong way through the sky, seeming to rise in the west and set in the east. Of course, the Sun still rises east and sets west, it just transits in the north! It was especially hard around midday, as the 10:00a sky looked like a 2:00p sky, and visa-versa. It really turns you around. Also, since they drive on the left side of the road, you always feel like you're functioning in a mirror image of the real world. At least the street signs weren't mirrored!
Like a bonehead, I neglected to consider the Moon's phase when scheduling the trip, and we left home during the waxing crescent. We missed the New Moon completely! In the southern sky, everything appears upside down, so during our three week visit, I followed what appeared to be an old crescent, which waxed backwards to full and then diminished into a new crescent. Also, the Man in the Moon was upside down, just like everything else.
On our first night in, Richard showed me Crux, the Southern Cross. At first I was kinda disappointed. It was a bit smallish, not even 10 degrees across. Without the little connecting lines you see on a star map, it looks more like a kite than a cross. Somehow, I don't think "The Southern Kite" would sound very impressive! However, before we left, I came to love Crux and would love to see it again. Over the night, Crux rotates clockwise around an invisible pole. The starry sky in the south seems to roll the wrong way over the span of the night. Never could get used to that lack of a pole star though. We really rely a lot on Polaris here up north.
It was a bit peculiar seeing the new stars of the south. They were strangers to me and I was an astro-newbie all over again. I quickly
learned that there's a cross-shaped asterism in Carina, in the Milky Way very near Crux. It's called "The False Cross" and it's easy to get fooled. You find the real Crux by "The Pointers" - Alpha and Beta Centauri - which are very bright stars. Other than that, I didn't learn many constellations and was pretty worthless at pointing the scope. However, there are many more stars in the southern sky and the Milky Way is larger and brighter. Also, the southern Milky Way includes a very cool dark nebula called the Coal Sack, which is inside the Southern Cross.
The Magellanic Clouds were something to behold, and you never saw anything like them in this hemisphere. I expected them to look like detached pieces of Milky Way, but they were very different. The Small Cloud was a little fuzzy patch, like a naked eye deep sky object. However, the Large Cloud was amazing to see, as big as an extended fist, and very conspicuous. It looked to me at times very much like a big ghostly skull, kinda scary looking, and once when it was very dark and clear, I decided to go inside rather than stare it down! It's hard to believe that the Large Cloud is only 55 degrees to the south of Orion and it's only a bit too far below our horizon to be seen here in the mid-temperate northern latitudes.
Many familiar northern constellations were easy to spot, but also upside down. It was kinda sad to see an inverted Gemini grazing the treetops at the meridian. The good part is, Sagittarius and Scorpius reach high in the sky, but they never got too high for me as it was the wrong time of year. Still, I was amazed to see how high Saggie can get even on an early summer morning before sunrise.
As in this hemisphere, the truly amazing constellation was Orion. From where we were at 40 south, he looked to be in about the right part of the sky, and conspicuous as ever. Being a fairly symmetrical constellation, Orion still looks much like himself upside down, except his legs make too long a torso and the sword is above his belt. The New Zealanders see an asterism in Orion called the "Iron Pot" where the sword is the handle and the belt stars are three burners under the pot. It really looks like that upside down. Also, it was funny to see Sirius at the upper right instead of the lower left of Orion. A couple times, I leaned really far backwards to look at Orion and see him 'right-side-up'. He then looked like himself but with nothing but stars and the Large Cloud beneath him, I had a feeling like I could fall off the earth into space.
Another new friend was Canopus, the second brightest star, close to Sirius in brightness. In ancient times, Canopus was visible above the horizon from the Mediterranean, but it's high in the sky in the temperate latitudes south of the equator. This star was near the zenith in the evening during our visit and usually the first star I saw after sunset.
I believe the southern deep sky is better than ours up north. Richard's stepfather was the director of the Ward Observatory, which houses a classic 9 inch refractor. He showed me my first sights of many southern objects. Herschel's Jewel Box is a fascinating cluster as it includes several bright red and green stars. Omega Centauri near Crux is huge, appearing as a fuzzy star naked eye at about 4th mag. It's too big really, as we had a hard time getting the whole thing in a single eyepiece field. Plus, its rather indistinct, and I didn't find it too interesting after a couple views. I much rather preferred 47 Tucanae, a tight compact globular near the Small Cloud, and thus very easy to find.
Other excellent sights include Eta Carinae, not far from Crux in the southern Milky Way. The observatory was in the city and quite light polluted, and through Richard's 6 inch newtonian, Eta Car was quite faint. You could still see a lot of detail, though I had a hard time identifying the lobe structure always seen in astrophotos. Another gem is the Tarantula Nebula in the Large Cloud, a huge object easily seen naked eye within the cloud.
As to the actual 'vacation', Debbie and I saw New Zealand's sights, including geothermal springs and geysers, glow worm caves and other local sights. The highlight was climbing Mount Ruapehu, an active volcano that last erupted in '95, after our visit.
We flew home on Feb 29, 1992. Our flight didn't leave Aukland 'til about 8 or 9 that evening, and New Zealand is the first time zone past the International Date Line. During the 12 hour flight home, we crossed back over the Date Line, picked up a day, and landed in LA early morning on Feb 29! By the time we made it home back east, and midnight the next day finally arrived, we had spent 42 hours living through Feb 29! Leap year that time around was so long, we practically had a Feb 30!
The night before we left, Richard and I were out scoping and we saw the rising of the upside down waning crescent moon, looking just like a boreal waxing crescent. Back in LA, I caught a look out the window and once again saw the waning crescent, restored to its correct orientation. Once again, the sky confirmed for me which hemisphere I was in!
Even in the short time we were gone, I came to miss my old friends the Big Dipper and Cassiopeia. Even though the northern sky doesn't have as much going for it as the southern sky, it's still 'our' sky! Anyway, I think that every astro buff oughta save his or her pennies and cross the equator at least once. You havent really seen the whole sky until you find out what you're missing.
clear skies!!! jay
* See related article elsewhere in this issue
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- Jay Ryan lives in Cleveland and produces 'SkyWise' for Sky & Telescope magazine. Prior to that, he provided 'StarMan' monthly in this newsletter. This article was received as an e-mail in November 1999 and is excerpted here by permission. [ -ed]
The next BMAA General Meeting is scheduled for Wednesday, July 5 at 8:00p
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ALAN'S (tongue-in-cheek) AMATEUR ASTRONOMER TEST
Answers from last month: 1 - A; 2 - A; 3 - A.
Tips for July
Eyepieces - part 2: aberrations and limits
- by Bernie Kosher
Eyepieces are just as important to the critical observer as the rest of the setup. The best scope in the world will perform poorly or not up to standards with inadequate eyepieces.
While good quality eyepieces (also called oculars) are not cheap, it is not always necessary to pay extreme prices. In some cases these expensive, wide field oculars will not perform as well as less expensive ones with simpler design.
So where do we go from here? The eyepiece best for your use is determined by. . .
1) the nature of the target,
2) the type of scope, and in most cases,
All eyepieces are a compromise of features. Eyepiece A may offer more field than B, while C may offer greater transmission. Or a longer eye relief. Or better correction of distortion and curvature of field. Which to pick?
Let's explain the common aberrations found in these eyepieces. Start with the simplest of all, a single positive lens. (A more complete explanation would require far more space and would be unnecessarily mathematical-while this is interesting to me, it most likely isn't to the person who wants a basic understanding)
The obvious aberrations are. . .
1) chromatic aberration (color errors)- the rays of different colors focus at different distances.The image is surrounded by a rainbow effect. Affects all of the field.
2) spherical aberration- the rays focus progressively closer to the lens from center to edge. There is no absolute 'focus', as the image is surrounded by a halo of out of focus rays. Affects the whole field. This is the prime cause of 'soft focus.'
3) curvature of field- if the center of the filed is in focus, the eyepiece must be moved in or out to focus off axis objects. This differs from 2) in that the rays are focused for some zone.
4) distortion- a straight line will appear to bend as it moves from the center to the edge. If the center of the line bows inward it is pincushion distortion, if outward it is barrel. Not a real problem for visual use, as it just shifts the position of off axis targets. In wide field photography it alters the appearance of the subject, and is very troublesome in photographic position measurements
5) coma- off axis images are fan shaped (see the literature for an explanation-it's a difficult concept, but easily seen). The fan can point in or out from the center. Affects off axis images.
6) astigmatism- the image is enlarged along one diameter more than one at right angles to the first. Oval images off axis.
There are others. For our purposes, we will be concerned with 1) and 2), the others to a lesser extent.
Bear in mind that these aberrations are all worse for shorter f/ratios, and are also caused by the objective of the telescope. In some cases, the eyepiece aberrations will partially negate the errors of the objective, but this is beyond the scope of this article. Many wartime surplus optics were designed as a pair, with the eyepiece annulling the objectives aberrations. These items should be tested carefully before being put to use in the amateur's scope.
A simple lens eyepiece will only be good in the very center of the field, as the chromatic and spherical aberrations would be intolerable for astronomical use.
Multi-element eyepieces are used to eliminate or minimize these aberrations. At least two elements are needed to even partially eliminate the flaws. Generally, the more elements the greater control the designer has over eliminating these errors. Different glass, spacings, and curves are methods used by designers, but this is far from simple and involves magic, intuition and pacts with the devil.
Not mentioned in the aberrations are such things as field of view and 'ghosts'. In theory, the larger the lenses the greater the field. However, in most designs only a limited amount of the field is usable due to color, spherical aberration etc. We'll talk about types of eyepieces and their limitations next month.
'Ghosts' are internal reflections caused by light bouncing off various elements. In modern coated examples, this is not a problem.
On older oculars it is extremely annoying.
Let's clear up something right now. A very expensive multi-element eyepiece is primarily designed to give a good image over a wide field. For use in short focus Newtonians, Dobsonians, and short ED refractors they are splendid and necessary for best wide field viewing. This does NOT mean it will perform better than a cheaper one for certain uses. In planetary and low contrast work the simpler eyepieces will actually outperform the 2 pound monsters. This is due to. . .
1) more elements means more absorption and reflection at various surfaces
2) more elements means more optical surfaces to make perfectly, to polish perfectly and to be perfectly clean:
the mechanical end must keep the elements centered and spaced: more cemented surfaces
3) more coatings means more scattered light (I would be interested in seeing some solid figures on this).
For these reasons it is difficult to defend their use as planetary oculars. A good Plossl, orthoscopic or symmetrical will give greater contrast. Yes, the field in perfect focus will be less, but the central portion, of concern to the planetary observer, will be slightly better. Perhaps best is the very old solid ocular, not available today that I know of. It's field is very small, but being a single element or single cemented element, it should be about the best for high contrast applications.
More next time. . .
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- Bernie Kosher provides 'Tips' monthly in the CONSTELLATION. He can be reached at firstname.lastname@example.org . [ -ed]
- by Jay Ryan
I had an idea that requires your input. You might remember that New Zealand story I wrote a few months back. That trip was a great astronomy adventure as it as a wonderful opportunity to experience the southern sky. As I've always told people, you haven't seen the whole sky until you cross the equator. It's an experience everyone should have, especially people in the astro-community.
So I got to thinking, maybe I could organize a group for a New Zealand astronomy tour? We always see these astro tours in S&T, sometimes through the magazine, sometimes not. Seems like a lot of southern hemisphere tours wind up in Australia, but I think NZ would be a more desirable destination. For one it's closer, and air fare might be cheaper. Also, the exchange is at an all-time low ($NZ1.00 = US$ 0.45) so it will never be cheaper.
A trip might include visiting NZ observatories. On Mount John, the University of Canterbury houses NZ's largest telescope. The United States Naval Observatory operates the Black Birch facility, and they might welcome a group of Yank astronomers. The itinerary could also include a stop at Mercury Bay where Captain Cook observed a transit of Mercury.
And of course, there's observing! We could go scoping under dark skies every clear night (and away from the cities, the skies are VERY dark and clear!) Perhaps such a tour could be timed to coincide with a big NZ star party (if such a thing exists). Being at 40 south, the NZ sky and climate would be familiar to Yanks, only inverted!
The southern sky offers the Magellanic Clouds, Crux and its pointers, and a pole with no pole star! Deep sky wonders include amazing globulars such as Omega Centauri and 47 Tucanae, the strange Eta Carinae, the Large Cloud's Tarantula Nebula and the colorful open cluster, Herschel's Jewel Box.
Also, besides the sky, there is much to see and do during the daylight hours. New Zealand has beautiful mountains, extensive limestone cave systems, and many volcanic and geothermal sights, such as geysers and the like.
So anyhow, I have no idea what's entailed with organizing such a tour, and that's where I need your input. If you like the idea of such a tour, let me know what you think about the following:
* How long should the tour be? 6 days? 10 days? longer? shorter?
* What season? NZ winters are mild (at least by Cleveland standards!) In June, it's winter, the nights are long and airfares are cheap. Sagittarius and Scorpius are about 15 degrees from the zenith after sunset and Crux and the Large Cloud are well placed. However, I can't say right now how reliable the winter weather would be. On the other hand, during summer (Dec-Mar) skies are reliably clear all the time and Orion is seen upside down after sunset.
* Should the tour feature elegant accomodations or economy? Airfare to NZ isnt cheap, and though I haven't looked closely, I'd expect $1000-$2000 from LA to Auckland. A poor working slob from Cleveland, I favor a budget trip.
* Should the tour be a basic tour bus deal, or should it be less structured to allow more personal exploring with appointed rendezvous places? Maybe it should be a "roughing it" sort of nature tour, with a lot of hiking, etc?
Anyway, this idea is in the "exploratory" phase, and if maybe 40-50 people could be reeled in, it might be worth it. So let me know if you have any thoughts, or any other ideas to offer.
thanks and clear skies, jay
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- Jay Ryan can be reached at email@example.com. [ -ed]