Stargazing

[stickmaker]

 

 

 

The Joy of High Tech

 

by

 

Rodford Edmiston

 

 

    Being the occasionally interesting ramblings of a major-league technophile.

 

 

Please note that while I am an engineer (BSCE) and do my research, I am not a professional in this field. Do not take anything here as gospel; check the facts I give. If you find a mistake, please let me know about it.

 

 

 

 

 

Stargazing

 

 

There is a saying about the sky: that on a clear night out in the country, you can see millions of stars with just your eyes. This isn't exactly right. On a clear night, in an area away from artificial lights with a full view of the sky and no light from Moon, someone with good eyesight can resolve about 3000 individual sources of light.

Perhaps the myth comes from the fact that under these conditions this person can also see multiple globular clusters, which - due to their distance - appear to be single sources of light. References mention that each of these clusters contains tens or hundreds of thousands of stars, leaving the impression in the uncritical mind that all of them can be seen individually. However, to the unaided human eye globular clusters actually show as - at best - fuzzy blobs, with no distinct points of light (except, perhaps, for nearer, individual stars between the observer and the cluster). There are no globular clusters close enough to our solar system for the individual stars to be resolvable without magnification.

Or perhaps people hear about the number of stars which can be seen with a telescope or good pair of binoculars under these conditions and simply accept that as the number which can be seen. Or perhaps most people who look up at night simply go "Ohhhh..." and don't bother counting.

(By the way, there's a similar myth that someone at the bottom of a deep shaft or tall smokestack can look up and see stars during the day. No, they can't. Even the thin air on mountain tops diffuses so much light that the brightest stars of the night sky are invisible during the day even well away from the Sun. Though occupants of aircraft at high altitudes (generally higher than 15 kilometers, which lets out people on airliners) can see stars during the day, due to being above most of that atmosphere.)

Under the ideal conditions described above a person with good eyesight which is dark adapted can note that many stars have a distinct color. Actually, most of them do, but the color is usually too faint to stand out, so the stars appear white. (Even the sun appears white when high in the sky and viewed through a neutral gray filter. (Do not look at the Sun directly with your eyes! Use a projection method or a sun-rated optical filter. Ordinary sunglasses or camera filters can actually make the damage worse.) The closer the sun is to the horizon the more its blue wavelengths are scattered, because the slant angle means a longer path through the air for the light. Therefore the Sun looks redder in the morning or evening.) 

Looking at stars can be deceptive in other ways, too. For instance, "empty" patches of sky appear that way not because of a lack of stars, but because dark clouds of gas and dust are between us and them. Many of these large clouds are stellar foundries, where vast, tenuous realms of gas and dust are slowly collapsing into new stars, bright and hot. (Remember the Hubble images of stars forming in nebulae?) Note that this activity is happening deep inside such clouds and is not usually visible outside. Once fusion starts the radiation pressure drives most of the remaining gas and dust away, "evaporating" the progenitor cloud. 

Even the brightest of these new stars may still be invisible to us if enough cold, dark material remains between them and the Earth. Fortunately, gas and dust are selective in what they block and what they pass. Depending on the makeup and density of the cloud, our instruments may see stars in radio or infrared which are invisible at shorter wavelengths. 

There are other reasons why a star may not be seen. Some very hot stars may shine brightly in UV but be invisibly dim - usually due to distance - in the narrow range of frequencies humans can see. A very cool star may shine brightly in the infrared but not be bright enough at visible frequencies to notice. If the source of electromagnetic energy is a black hole most of what comes out can be x-rays or even higher frequencies.

  Gravity, though, comes through regardless. Some massive bodies are known to exist only because of their effects on other objects. If a cloud is collapsing radially inwards, there's got to be something inside with a lot of mass, even if it's just an unusually dense (though still more tenuous on average than the "vacuum" a high school physics class vacuum bell jar can produce) clump of material which will eventually form a star. 

Which brings up an important point. Even when you can believe your eyes, there's almost certainly more there than what they show you. Much of the universe went unnoticed by humans until they started developing the tools to spot effects which were not obvious to our unaided senses. Many of the earliest of these tools were mathematical. Carefully collecting and analyzing data will often reveal inobvious effects. Neptune, for example, was discovered because of the effects of its gravity on other planets. 

Unfortunately, many people won't believe anything which they can't see, hear, smell, taste or feel for themselves. Drawing inobvious conclusions from data strikes them as, at best, frivolous. In cultures making the first steps away from an animistic view of the world towards a pragmatic analysis of cause and effect, this trust in things unseen can even be thought of as a backwards step. This unfortunate characteristic applies to many fields besides astronomy, but it was there that some of the greatest clashes between what tradition taught and what new tools revealed have occurred. 

Building tools to look at something new is usually expensive and difficult. There were good reasons the 200" Hale Telescope was the largest in the world for decades, and remained the only effective telescope in that size range for decades after a larger one was built. The Hale pushed the state of the art for optics, control mechanisms, support mechanisms and several other technologies to new levels. (It did the same for funding!) For example, it was the first telescope to use Pyrex for the mirrors, and this only after attempts to make large blanks from fused quartz failed. While those same technologies could have been used for a still larger telescope, affording it and getting it right would have been incredibly difficult. (As the Soviets found out.) Building a good telescope with greater light-gathering power and being able to afford it required yet newer technologies. 

Those have been developed, and today there are several high-quality, large telescopes which outdo the Hale in aperture, with more planned. A few have the same type of single, monolithic mirror as the Hale, but most are two or more mirrors which work together. Some - using such tricks as adaptive optics to compensate for atmospheric distortion - rival the Hubble in sharpness, though unlike telescopes in space they are still dependent on good weather. Improvements in both sensors and data-analysis techniques mean that we can also squeeze more out of what older telescopes, such as the Hale, can do. Additionally, the Hale remains popular for testing new equipment, because a weighty, bulky prototype can be attached to it and the mounting barely notices. With these devices and their production versions, the Hale still does valuable work.

You don't need a huge telescope to make important contributions, either. Today even amateur astronomers have tools - both for observation and for analysis - which would have seemed like wizardry to Kepler, Galileo and Newton. Telescopes of large aperture (in comparison to professional instruments of even a century ago), low light loss mirrors and lenses, excellent precision and high physical and thermal stability are available for quite reasonable sums and in a short amount of time after placing the order. Even some surprisingly large-aperture telescopes made today are portable. Filters for various types of observing help block out what isn't wanted while allowing the important stuff through, making revealing observations easier. Cameras of various types - most of them high-quality digital devices these days - detect things which would escape the human eye or even hypoed photographic film, and they're attached to equipment which directly records the information these gather. Computers then organize that information. 

Yet, it is still the operator who makes all these tools capable of doing important work. While several automated telescopes for performing various types of sky surveys have been attempted and better ones are planned, even those which worked only did their jobs. Because a machine can only do what it is made to do. You need a living mind to take notice of something new. With the excellent equipment available these days to even amateurs, there are more well-equipped astronomers around the world now than at any previous time in history. These amateurs are doing far more than engaging in a moderately expensive, time consuming hobby. Most new comets are still discovered by amateurs, or by low-level professionals without access to major instruments. As are many asteroids. (Even naked-eye observations can still provide good data of some phenomena.)

Stargazing is under threat from many quarters these days. Light pollution is a concern even for the Hale Telescope at Mount Palomar, and current politics make people standing outside in the dark with large pieces of equipment targets of investigation. In spite of these problems, Astronomy still thrives, and continues to be a field where anyone with determination to learn and work can make an important contribution. 

Comments

[kengr]

One "interesting" bit of naked-eye astronomy occurred in the 50s. Back then the replacement lens used in cataract surgery were made of quartz and were thus transparent to UV. (Modern replacements block UV)

So one astronomer who'd had the surgery wrote a nice article for one of the astronomy mags on *naked eye* UV astronomy. Apparently the sky looks significantly different if you can see UV.