Misplaced Pages

Revision as of 22:07, 1 August 2008

The topic of this article may not meet Misplaced Pages's general notability guideline. Please help to demonstrate the notability of the topic by citing reliable secondary sources that are independent of the topic and provide significant coverage of it beyond a mere trivial mention. If notability cannot be shown, the article is likely to be merged, redirected, or deleted. Find sources: "Skygazing" – news · newspapers · books · scholar · JSTOR (November 2007) (Learn how and when to remove this message)

This article contains instructions, advice, or how-to content. Please help rewrite the content so that it is more encyclopedic or move it to Wikiversity, Wikibooks, or Wikivoyage.

This article may require copy editing for grammar, style, cohesion, tone, or spelling. You can assist by editing it. (January 2007) (Learn how and when to remove this message)

Skygazing is the act of observing the sky. It is done for pleasure or with an astronomical interest. Amateur astronomy observations are generally accomplished with the naked eye or with basic optical aids. When approached with a practical stance, skygazing quickly reveals the magnificence of celestial objects. Simple naked-eye observations of the sky can reveal a great deal about the basics of astronomy, a better understanding of the cosmos, and can be extended by using powerful instruments to study deep space.

Naked eye skygazing

Diurnal observation

The extreme brightness of the Sun saturates the sky and prevents naked eye observation of less luminous objects, with the exception of the Moon and occasionally Venus.

Sunspots and solar eclipses can be viewed during the day using a telescope or binoculars fitted with approved safety filters. Extreme caution must be exercised to avoid permanent blindness. Some solar filters supplied with cheaper telescopes are not safe enough. Only filters clearly identified as complying with current safety standards should be used. and

Eclipses

One of the sun's most spectacular phenomena is a partial or total eclipse. Solar eclipses only occur when the moon is in the New Moon phase (which occurs every 29.5 days), however, eclipses cannot always be seen in these periods, because the moon goes "above" or "below" the Earth as it orbits. The moon's orbit is tilted by about 5.2° away from the plane of the Earth's orbit around the sun. During this period, the Earth, sun, and moon are aligned only during certain times of the year. During eclipses, from the vantage point on Earth, viewers witness the moon slowly moving partially or totally past the sun, (one recent example being in France on August 11, 1999). The diameter of the moon and sun appear almost equal, although in reality the sun is much bigger, it is also much further than the moon and therefore appears smaller. This allows the moon to totally block out the sun during a solar eclipse. Sometimes a ring made by the sun shining past the outside of the diameter of the moon is also visible; this is a special type of total eclipse, called an annular eclipse. In the total eclipse zone, it is possible to see the most brilliant stars in the daytime, and especially Mercury, which is usually difficult to observe because it is always very close to the sun.

Sun

Sun spots

Sun spots are difficult to see with the naked eye. They are effectively solar disturbances on the sun's surface and can change over time as conditions within the sun change, somewhat like storms on the sun. By observing the sun over time the appearance of sun spots changes due to both the sun's rotation and each storm's evolution.

Advice for spotting sun spots

Looking directly at the sun during the day can be very damaging for your eyes. Not even sunglasses will prevent eye damage, so special filtered glasses fitted with materials such as metallized PET film are essential. These can also be used to observe solar eclipses. However, sun spots can be seen safely when there is a sufficient level of fog or cloud. Projecting an image of the sun on to a surface using a piece of card with a pinhole can also be very effective, and safe.

Aurora Viewing

Aurora is a typical skywatching activity especially at higher magnetic latitudes.

Cometary Viewing

Comets can be easy to locate and photograph and an excellent reason to skywatch.

Atmospheric Optical Phenomena

Phenomena linked to the Sun and Moon: Other interesting observations in relation to the Sun and Moon (even Venus at times) can be made, although their observation depends on the particular atmospheric conditions. These can be easier to observe since they do not always require any eye protection.

• The solar halo

Phenomenon that can be seen mainly in winter and in altitude, it presents itself under the form of a big luminous club, little extended in its width and centered on the Sun. It shapes itself by the refraction of the solar rays through a fine and uniform coat of high altitude clouds, the cirrostratus. Often requires eye protection, as the sun is within the field of view

• Rainbow

Visible during or after a rainy period with a partially clear sky, it is a bow of white light refracted into all the visible colours of the spectrum by solar rays through raindrops. In optimal conditions, a second bow less luminous, with reversed colours, can be observed (see picture at right), the space between the two being slightly darker than the rest of the sky.

• The parhelions

Invoked like the halo but by other clouds and more frequent, these are two luminous spots to the often defracted colors like in the rainbow and situated on both sides of the Sun to a similar distance very close to the club of the halo and capable to associate to this one.

Nocturnal observation

If you have a good view, don't hesitate to you start the conquest of the sky. Indeed, it is possible to distinguish in the celestial sphere, during a dark and moonless night, about 3000 stars.

Moon

The queen of the night - its observation by the naked eye permits us to approach our only natural satellite and to understand the alterations that affect it better.

• The phase of the Moon

They explain how to do themselves by the position of the Moon, the Earth and the Sun in the space.

Its light coming from the only reflection of the Sun's light on its surface, the Moon will present the appearance of one end visible crescent to it twilight or to the dawn when it will be located between the Earth and the Sun, a half visible disc during the half of the night when it will be to the same distance of the Sun that our planet and finally a present complete disc all night long when it will be to the contrary of our star in relation to the Earth. The entertainment of one end crescent moon on the blue sky sinks, at twilight, is worth to stay late for its contemplation.

A game of paths of luminous rays also carries the attention: in its first upward phase or its last downward phase, when it is only a crescent, one can notice that its dark side, to the shade, presents a weak gleam on all its surface permitting to distinguish the form of the complete disc. It is due to the solar rays, think a first time by the Earth toward the satellite, then a second time by this one toward us. This long course makes that a weak quantity of light reaches us, but sufficient to distinguish it.

• The lunar craters

These are pits or depressions in the surface of the Moon, produced by great impacts of gigantic meteoroids which mostly took place billions of years ago. They range in size from huge walled plains more than a hundred miles across to microscopic pits. The smallest craters which can be glimpsed through ordinary binoculars are about twenty miles across. These craters are most common in the light-colored Lunar highlands. They are named after historical figures, mostly scientists.

• The Lunar Maria (seas)

Of different and darker composition than the rest of the surface, the maria (singular "mare", Latin for sea) are composed of basalt. These flat areas of ancient frozen lava form the familiar pattern of dark spots which can be seen with the naked eye. They are given the names of fanciful bodies of water since early observers believed them to be literal seas. Charts of the Moon are available to aid the observer in identifying Lunar features.

• The eclipses

Following the same principle with the solar eclipses, the lunar eclipses only take place when the Moon is full and that the Earth is placed between the Moon and the Sun. The diameter of the shadow of our planet being a lot bigger than the one of our satellite, these take place more frequently and have the same appearance whatever is the position of the viewer on the Earth. At the time of the total phase, the Moon remains visible and has an orange color that is due to the deviated solar rays and tinted by the terrestrial atmosphere.

• The lunar halo

Invoked by the same meteorological phenomenon that for the solar halo, this one presents itself however under the appearance of a luminous disc in the more vivid diffuse side and a more reduced diameter than its diurnal equivalent.

The planets

As the night passes, a viewer will notice some stars move more quickly than others. They are actually planets. To distinguish a planet from a star, it is necessary to know that the stars flutter and the planets little, because of the a lot more important distance that separates us of the first. Once you found a planet, it is not uninteresting knowing about what it is and it is, even to the naked eyes, comfortably feasible. Indeed, all visible planets have some features peculiar to them:

• Mercury is rarely visible from Earth since its orbit keeps it very close to the Sun.

  

• Venus, also known as the "Shepherd's star", is white in color, and appears brighter than any object in the sky after the Sun and Moon. Visible near twilight and dawn, like Mercury, Venus is an interior planet (one whose orbit lies between the Sun and the Earth) and appears to follow the Sun relative to our perspective (its maximum elongation is 28°). Its apparent magnitude varies depending on its phase (very much like the Moon) as well as its distance from Earth.

• Mars is not unusually bright, but it can be distinguished from other celestial bodies by its reddish light. A casual observer (over the period of several days) may notice that it seems to make a U-turn (stops and then moves in retrograde): this is a property Mars shares with all the outer planets, and is owed to Earth's relative movement around the Sun. In the case of Mars, this takes place roughly every two years, with the period of greatest change in its apparent motion taking place over two months.

• Jupiter is pale in color. Although bright enough to be confused with Venus, a viewer can recognize it instantly: if one observes the equivalent of Venus in the middle of the night, it is Jupiter.

• Saturn is considerably less bright than Jupiter (Uranus and Neptune are dimmer still). Besides the planets, there are many other celestial curiosities:

The Milky Way

The Milky Way is constituted of a denser roundup of stars in relation to the rest of the sky and represents the bracket of our galaxy viewed from within.

Stay one night in a place far from the bright lights of big cities so that your eyes get used to darkness, and wait and relax, observing the celestial arch. Scanning the myriad of stars that constitute the Milky Way is one of the biggest spectacles of skygazing. In summer you will see a gigantic milky irregular bar crossing the arch, this appearance giving it its name since the Greek antiquity.

The constellations

These are not strictly speaking celestial objects since they constitute a grouping of stars making the shape of a figure, in general that of an animal or a mythological being, this nomenclature dating back to the Ancient Greek times for the stars seen in the Northern Hemisphere. Charts are available that show a complete view of what stars are visible at any given time on Earth. Astronomy 101 is based on these star charts, enabling the reader to navigate amongst the stars, using the Polaris star as a celestial north-pointing compass to be able to find the brightest of the stars: the Andromeda galaxy or the most luminous star of the sky (Sirius of Canis Major) for example. The Little Dipper (right photo) is not a constellation but is an asterism within the constellation Ursa Minor.

The other celestial objects

• The meteors

As extending your observation you will notice some light cells follow a trail crossing the sky quickly: the "falling stars". These are the meteoroids that often don't weigh more than one gram but ignite when heated up by the abrasive action at the time of their penetration into the denser terrestrial atmosphere. One can see several scores of them in one night. Some nights are especially favorable for their observation because the Earth, in its orbit, crosses regularly the clouds of meteoroids as it is well known to the astronomers (see the item "falling star" for the dates). Other phenomena are accessible to the naked eye, such as the comets, interesting and sometimes magnificent like Halley's comet as seen in 1910. There are also various objects (galaxies, star clusters and nebulas) visible to this level, but only under the appearance of milky spots save for the Pleiades in the constellation of Taurus where one can distinguish the different stars.

Advice for the nocturnal observation

The observation of the Moon adapts to practically any condition, but for all other skygazing endeavors, the first piece of advice is to move away from all artificial lights; avoid cities because of their strong lights and pollution-created haze. Move away from big towns to get the darkest possible sky. For the same reason, avoid moonlit nights, especially when the moon is full, because its intense clarity hurts the observation strongly. The eyes need time to adapt to the obscurity (about 15 to 30 minutes) to develop their full capacities in these conditions. Any intense luminous ray (headlight of car, pocket-size lamp, etc.) "destroys" this familiarization and reduces strongly its capacities. To avoid this problem, place a piece of opaque adhesive tape (preferably red) on your pocket-size lamp so that the least amount of light necessary for reading a sky chart will be available and nothing more.
For the best observation of the sky, choose an open area giving the largest possible field of vision. Mountains are excellent choices because they have a large field of vision due to being above the tree line.
Camping out to watch the sky can be a wet and cold process, so be sure to bring warm clothes. Also, foldable chairs will be comfortable to sit in for longs periods of time, offer a good viewing angle, and reduce strain.

Binocular gazing

Binoculars are very useful when you wish to observe bright, large astronomical objects. Thanks to them it is possible to see lunar craters. In spite of the distance between us and the Moon, one can observe the relief of these craters along the terminator, the separation line between the illuminated and darkened parts of the Moon. Lunar features are emphasized in this zone where sunlight strikes at a low angle and casts long shadows. This spectacle is a good start to skygazing due to its ease.

Binoculars are good for the observation of large nebulas and the occasional bright comet. The reason is due to their very nature: the binocular enlarges images and adds brightness compared to naked eye views. Very extended objects can be seen in their entirety due to the wide field of view (which may not be the case with a telescope and its greater magnification) and with improved clarity and contrast compared to the naked eye. The Orion nebula is one of the most luminous and one of the easiest to locate. It is situated in the constellation of Orion, a constellation visible in winter, big and easily recognizable with its rectangular form and a short row of three bright stars forming the belt of Orion. One can also observe the cluster called the Pleiades, a stellar heap composed of over fifteen stars which can be found by extending one of the diagonals of the rectangle of Orion toward the northwest. Also visible in the late summer, fall and winter is another striking spectacle which lies beyond our own Milky way galaxy, the Andromeda galaxy. Though faintly visible to the naked eye, locating this object requires one to know how to identify the main constellations (see Locations of the constellations). The constellation Andromeda is situated under Cassiopeia in relation to the polar star. While viewing the Beta star of Andromeda in the binoculars, one ascends very slightly toward Cassiopeia until one sights a first small star, then one ascends again very slightly until one sees a fuzzy patch of light which is the heart of the Andromeda galaxy. If sky conditions are good, you may also see a surrounding very diffuse oval that represents the arms of the galaxy. This vast collection of stars is located 2.5 millions light year away! It is one of the more distant objects that can be seen in common binoculars.

With experience, so long as the binoculars are held steadily and with decent atmospheric conditions, viewers endowed with good vision will be able to discern the four Galilean moons of Jupiter, even with simple 8 x 35.

Choice of binoculars

Their features are determined by two numbers : the first number indicates the magnification, the second the diameter of the lenses in the front, or aperture. Large apertures are recommended because they will collect more light and so reveal fainter objects. Thus, while a birdwatcher might prefer a compact 8x35 binocular, a skygazer will do better with a larger 10x50 glass.

Advice on observational techniques

It is strongly recommended to fix the binocular to a tripod (used for photography, for example) in order to steady it, ensuring comfortable observation and helping the observer to avoid losing the field of the object. Some models of binoculars are equipped with a tripod socket for easy attachment, but some adhesive tape will do the job in a pinch. Adjust the binoculars in order to get the best possible picture by focusing and adjusting the distance between the eyepieces to match your own eyes. If you wear glasses for astigmatism you'll probably want to leave them on. Otherwise you should be able to focus the binocular sharply even without your glasses.

Important warning : Never attempt to observe the Sun with binoculars. Special solar filters for binoculars exist, but are hard to find. In direct observation, the power of the concentrated light would burn the eyes irreparably. A similar example would be that of a magnifier which sets fire to a sheet of paper or a piece of wood.

Observations with a refracting telescope

A refracting telescope is an instrument containing at least two lenses which focus light into an image at the focal plane. An eyepiece situated at the focus functions as a magnifying glass which works by permitting the eye of the observer to focus on this image at very close range, causing it to appear magnified. A good refracting telescope can be an instrument that one retains all his or her life, even after the acquisition of a bigger telescope.

The usually small aperture and general precision of refracting telescopes makes them well suited to the observation of objects which are bright and detailed, such as the Moon and planets. Even a small model of 60 mm of diameter wll reveal some detail on planets, and much detail on the Moon.

Jupiter is an ideal target for the first-timer equipped with a refracting telescope. Its observation lets us see the four main companions of the planet which are the Galilean moons as well as some details to the surface of the planet clearly. It shows how much the astronomical observation is a discipline of patience. Those expecting great entertainment might opt for a more powerful telescope whose operation requires a finer mastery of the basics of astronomy. It is well nowadays with a telescope less effective than all those sold in the business that Galileo discovered the moons of Jupiter and that he acquired the conviction that Copernicus had reason of it: the Earth moves!

With a refracting telescope, it is also possible to follow the phases of Venus and the change of its visible diameter with the passing of the months. Mars appears like an orange disc, but often without the least detail. One can follow however also there the fluctuation of its visible diameter all along the year. In a good configuration between Mars and the Earth, when the red planet is to the nearest, it is possible to distinguish its polar cap.

The most distant bright planet that one can observe with the refracting telescope is Saturn. If the conditions of observation are good, it unveils the very beautiful spectacle of its rings. One can follow the change of their appearance. In 2002, they were seen at their widest angle and best presentation, and will be seen in profile in 2010. They will then completely invisible for a few days, after which they will again appear as a thin, bright line as the angle gradually increases once more. Meanwhile, their appearance changes from year to year. With experience it is also possible to distinguish the large moon Titan.

The refracting telescope is an instrument perfectly appropriate to the survey of the Sun, but drastic precautions must be taken to avoid any burn of the retina. When these precautions have been taken, the Sun unveils its details distinctly. One can see it evolve day after day and move because of its rotation. It is also possible to observe more distinctly than with nebulous certain twins (M42) or globular clusters (M13). Finally, let us not forget the Moon, on which a multitude of details offers themselves to you: craters, mountains, etc. As with binoculars, it is the observation to the level of the terminator that reveals the more of details, notably the reliefs of the Moon.

Choice of the refracting telescope

The main optical problem of refracting telescopes is chromatic aberration (color fringing). When one observes a planet, the Moon, or a bright star at high magnification, it will be surrounded by a diffuse glow of unfocussed color, usually blue or violet. This effect can be minimized by the use of a lens with a long focal length, but this can result in an unwieldy instrument. Refractors can be made essentially free of false color using various apochromatic designs, many of which use three lenses (a triplet) as opposed to the two lenses (a doublet) found in the more common achromatic instruments. This system is costly. Refractors of this type can be less awkward because lenses of a shorter focal length can be used, resulting in a shorter telescope. It is difficult to construct refractors of more than 150 mm of aperture because of the expense of the raw glass and the possibility of breakage in manufacturing. Let's add that a refractor is expensive in relation to a telescope of other design on the same size. 60 mm diameter refractors are cheap, but from 100 mm and up they can be three times as expensive (or more) than a mirror telescope of the same aperture.
On the other hand a telescope can transport itself comfortably because it doesn't go out of order easily (goal is steady), which is a certain benefit. Otherwise, in a telescope, the objective is not obstructed in part by the secondary mirror that one finds in reflecting telescopes, what enhances the quality of the picture, the full surface of objective being used to collect light. The best choice (but also the costliest) is the apochromatic telescope that corrects all aberrations (chromatic and spherical).

Advice of usage

Sun

Its observation, again same with binocular (see above), must come with the strictest safety measures. The burn of the retina is painless, but it is irreversible. It is therefore necessary to use the filters of which exist two types : the Sun filter, amounting to the back on the eyepiece, often sold with the telescope. Its only usage is not adapted because it is submitted to strong temperatures that coalesce it to explode quickly. Its usage must be combined with the helioscope of Herschel that disperses the heat. This accessory is generally on sale that in the specialized shops. The second model stands in the front, on goal, and reduced the luminous flow before its entry in the instrument. Costlier, it is the safest solution, under the condition to use the suitable filter. This solution has in its favor a double avantage: disposed out of the optic system, therefore to ambient temperature, there is not any hazard that it breaks because of the heat. On the other hand, placed before the telescope, before doesn't shape itself the picture, its shortcomingses will influence less on the quality of this one that the first type of filter installed on the just eyepiece before the eye.

In any case, check the installation carefully before starting the observation of the Sun. It is never ridiculous to place a sheet of paper behind the eyepiece in order to confirm that all is in order and that the brightness is not too strong: your eyes are priceless.

Moon

At its full phase, it can appear spectacular, but otherwise makes little interest of itself. Indeed, having it from the Earth a parallel vision line to the Sun, one cannot distinguish shades on its surface that permit us to see the details of it. Thus, prefer the periods before or after this stage and concentrate the observation on the zone to the limit of the illuminated party and the one to the shade, where the rays shine its surface and give the best reading of the craters.

Note that some filters also exist for placing on the eyepiece at the time of the observation of the Moon in order to not to be dazzled by the very strong clarity of the Full Moon. Unlike the Sun, there is no hazard in case of oblivion of the filter when gazing the Moon. Its usage is recommended however because it filters the UV reflected by the surface of the Moon. The Moon filters must not be used for the observation of the Sun.

The observation with a reflecting telescope

A reflecting telescope is constituted not of lenses but of mirrors. It being less costly to manufacture, one can, for the price of a refracting telescope, acquire an instrument of the more important diameter that gives access to the deep space. Nevertheless, to take advantage of the power of a reflecting telescope, it is necessary to have a good site of observation safe from the lights of the city, otherwise the usage of a good telescope is preferable.

With a 150mm lensed reflecting telescope, the viewer is able to distinguish the spiral arms of some galaxies and details in many stellar or star clusters. With such an instrument, most of the Messier objects can be appreciated in good details. These instruments are also very interesting when they are used for planet-gazing which they reveal, thanks to their best power of annulment, a multitude of details as the Great Red Spot of Jupiter, visible with a telescope of 200 mm or the Cassini Division in the rings of Saturn. It becomes possible to follow the alterations of appearance of the main planets of the solar system with the passing of the months, and the craters of the Moon appear with all their details on the terminator.

A sufficiently powerful reflecting telescope (300mm) opens the way to hunt for the comets, the holy grail of the amateur astronomers. All of them dream to be the first to discover a new star to which they will give their name. The hunters of comets constitute a world a little to part in the astronomy hobbyist. Besides being an expensive material, the research of comet requires a big rigor because it demands systematic observations, but some hobbyists count close to about ten of these stars on their chart of hunt.

Some either the type of observation led, it is while getting involved in the astrophotography that one gets the best part of its instrument. As lengthening the time of exposure, the brightness and the contrasts of the picture permits to reveal the thinnest details. The best solution accessible to everybody is the use of a sensor CCD connected to a computer. These sensors are built in all electronic devices with capacities of taking images (webcam, digital camera, cell phone, etc.). The present sensors in these devices can be used in CCD astrophotography, but the best pictures are taken with monochromatic sensors. In any case, a little tinkering is necessary. The hobbyist of astronomy who wants to become amateur astronomer must start learning the fundamental principles of the optics to be able to achieve their own tinkerings because some instruments of optimal performances are not sold in the store.

Types of reflecting telescope

There are two popular types of reflecting telescopes : the Newtownian and the Catadioptric.

The Newtownian type telescope		The Catadioptric type telescope (Schmidt)

The Newtonian

The Newtonian type is characterized by a long enough tube, a bit lower in its focal length and is composed of a parabolic main mirror to the substance bound to a flat alternative mirror close to the opening, oriented to 45°, that return the light outwards through the eyepiece. The observation makes itself therefore by the side of the tube that is open and will let dusts to enter and deposit themselves on the mirror. Its another inconvenience is that the temperature inside the tube is slightly higher than the temperature of the surrounding environment (at least in the beginning of the night), the hotter air, while escaping, will invoke the turbulences that will harm the quality of the picture.

Types of Catadioptrics

The Schmidt

The Schmidt is a design that uses all spherical surfaces, making it an instrument that is easy to manufacture. It employs a cassegrain design with a compound curve corrector plate at the front of the tube that "corrects" all the aberration a spherical system would have (and also gives the telescope the advantage of having a sealed tube). The secondary mirror in a Schmidt is mounted on the corrector plate.

The Maksutov

The Maksutov, is similar to the Schmidt except it uses a thick concave corrector plate and the secondary is usually a silvered spot on the backside of the corrector (a "spot-mak"). This design has the added advantage over a Schmidt in that it never needs alignment, all optical elements are fixed in alignment.

The big benefit of the reflecting telescope on the refracting telescope is its manufacturing cost, what permits to acquire for a reasonable amount an instrument of bigger diameter, lien of a big necessary brightness at the time of the observation of the distant and weakly luminous objects. Otherwise, the chromatic aberration doesn't exist with this type of instrument, but the alternative mirror overlooks goal in part, what is an inconvenience (loss of brightness of the order of 5 to 10%). A telescope, unlike a telescope, asks for an entretien : the primary mirror has a certain degree of freedom in the tube and can in some cases (a physical shock for example) to go out of order, requiring a realignment that one undertakes oneself thus. This same mirror being coated of a very fine coat of aluminium, deteriorates to the contact of air and has a life of 8 to 10 years. Specialist firms take care of the transaction.

Gallery

• Airisation in cloud over Wellington NZ
• Aurora Australis and the Crux
• Aurora Australis Display Over Wellington 2001
• Comet Neat over Wellington 2003

See also

• Amateur astronomy
• Astrophotography
• History of Astronomy
• Sky
• Telescope

External links

• Solar Eclipses for Beginners
• The Night Sky This Week
• AstroFind - Search Engine for Astronomy
• Clear Sky Clocks Weather forecasts for astronomers in North America

• Articles with topics of unclear notability from November 2007
• Misplaced Pages articles needing copy edit from January 2007
• Observational astronomy