Astronomy

Astronomy is bigger than all of us. It's looking up into the sky and wondering. It's Stonehenge and the Transit of Venus. Astronomy is Polynesians using the stars and calmly setting sail across the Pacific at a time when European navigators didn't believe it was possible. Astronomy is ancient civilisations working out if the gods were on their side. Astronomy is stories, songs and poetry - it's all written in the stars.

The greatest explorations of our times are in space. We are learning more about our universe right now than at any other time in our history. Carter Observatory

Much of the astronomy carried out by professional astronomers these days occurs in remote areas, far from the lights of civilisation, either on remote mountain tops, or above the light polluted atmosphere of our planet - in space itself.

Amateur astronomers and the general public are not usually so fortunate. With trends towards city and urban dwelling, most of the world's population in developed areas, do not see the richness of a sky filled with stellar treasures. In New Zealand 87% of the population live in Urban areas.

Today, even remote areas are being exposed to increased illumination from light pollution or "sky glow," the combined lights of cities and towns, sometimes hundreds of miles away that produce a dull glow in the night sky.

The southern winter sky includes the constellations of Sagitarius, Scorpius and the Southern Cross.

Select a zone to see the available night sky.

Rural Sky

Figure 1

"If something is not understood, it is not valued;
if it is not valued, it is not loved;
if it is not loved, it is not protected,
and if it is not protected, it is lost."
Unknown

"The views of the night-sky from Dumpling were stunning on clear nights and this was a great opportunity to point out some of the stellar features to those from light and air polluted habitations. Dark Skies for most people can now be placed on the rare and endangered species list!"
Hut warden, Dumpling Hut, Milford Track, Fiordland, New Zealand.

Limiting Magnitude

Night skies can be rated by their limiting magnitude--a term astronomers use to describe the faintest star visible to the naked eye. A total of 15,000 stars are visible under a magnitude 7 sky, characteristic of a sky without light pollution. Heavily lighted urban areas typically have a limiting magnitude of 3 or 4, where only a couple hundred stars are visible. Click on the zones above to show the Milky Way under magnitude 7, 5.5 and 3.5 skies.

Astronomers were the first to notice the effects of sky glow, as faint celestial objects billions of miles away began to disappear from their telescopes. Now other scientists, primarily ecologists, are realizing that the ecosystem effects of artificial night light can be subtle to severe. For billions of years, life has evolved with established day and night cycles that both nocturnal and diurnal species have adapted to. For example, many birds migrate at night using the stars and glow of dusk and dawn for directional orientation. Many nocturnal reptiles and amphibians use darkness to their advantage to hunt and forage. For diurnal species, those that are awake during the day and sleep at night, nighttime is important for finding shelter and hiding. Ecologically, light pollution changes these normal behaviors, especially for organisms that require certain degrees of darkness and are far more sensitive to light levels than humans are. These organisms are correspondingly more affected by light level changes. In addition to having ecological effects, light pollution affects Wilderness character. It's difficult to imagine camping "underneath the stars" without the view of the cosmos above. Even today, one must often travel to the most remote places to experience truly dark skies.

To Observe the Night Sky

First, as often as possible, observe away from city lights.

Through all of history - until the 20th and 21st centuries - the sky was dark at night even in the world's major cities, and (ignoring chimney smoke) the stars shone as brightly over Auckland as over a rural Southland town. Our modern cities are bathed in a perpetual twilight from the millions of lights that illuminate the air itself, not to mention any dust, smoke, and smog in the air, and this lets us see only the brighter stars.

Astronomers refer to this unwanted stray light as light pollution and the RASNZ campaigns against inefficient lighting. Children who grow up in the city do not know what the stars look like and have no appreciation for the beauty of the sky, and even adults often forget. It is common to hear an audience gasp and even applaud when the stars come out in an urban planetarium show.

People are most aware of the poor quality of an urban sky when a bright comet appears and they are told by the news media to "go to a dark site" to see it properly. Even if a comet can be seen from within a city, it is a pale shadow of what people see from a dark location.

Many people conduct their most rewarding stargazing while on vacation. The national parks and national forests are generally exceptionally dark at night, and the sky becomes an attraction once darkness has settled over the trees, meadows, and waterfalls. Take binoculars or a spotting telescope on your next vacation and continue to sightsee after sunset.

Star Magnitudes

For professional, amateur and recreational astronomers the visibility of sky objects is paramount. If you can't see it you can't study it without using advanced and expensive technologies such as radio, infra-red, x-ray or gamma-ray telescopes.

The brightness of a star, or its visibility, is expressed in magnitudes. The brightest visible stars were intended to be first magnitude, the faintest seen by the eye, sixth magnitude. In clear, dark skies good eyesight will see down to about magnitude 6.5. Each 5 magnitude step is a hundredfold change in intensity. Thus 10 magnitudes are 10,000, 15 magnitudes one million. Each 2.5 magnitude step multiplies or divides by 10. The scale is negative, with the brightest objects having the smallest magnitudes. See Figure 2.

Star Magnitudes

Figure 2

The realm, beyond the naked eye barrier of 6.5, was at first explored in 1609 when Galileo aimed a telescope skyward. By focussing extra light into your pupil, even a small telescope takes you to the 12th magnitude. A $100 telescope can increase every star's apparent luminosity a few hundred times. Compared with the naked eye, this is a gain of five or six magnitudes at a cost of just $17 per magnitude. As telescopes get bigger, the cost per magnitude climbs dramatically. A 600mm telescope costing $40,000 will brighten things by just 1.5 magnitudes over a 300mm scope that costs $4,000. The Palomar (5 metres) or Keck class cost millions of dollars per magnitude. Brightness is not cheap.

Figure 2 shows one effect of light pollution of night skies. The figure shows the range of the stellar apparent magnitude system. The left column holds the numerical magnitude range while the second column lists objects that appear at that magnitude level. The 'Comments' column presents some further information at each level. Included in this column are indications of the range of advantage that telescopes of various sizes can give. Indications of costs for these telescopes are included.

The fourth column indicates the effects of a polluted sky. If the naked eye limiting magnitude is reduced to around 3, from 6.5, the sky has been brightened by a factor of 2.51^3.5 or 25 times. This imposes a cost on the astronomer who needs to purchase larger more expensive telescopes to see stars that should normally be visible. Other alternatives for astronomers are to travel to dark sites, which imposes costs including time and travel, or when using photographic or similar equipment extending the duration of the exposure in order to capture the faint stellar image.

Figure 3