Basis

Well. Here you are, at your camp site, or at your vacation resort. Night is coming and you would ike to know more about the night sky which is progressively appearing as the twilight darkens above! Two tutorials are going to be of help to you. The first one, named 'What's the Night Sky?' is introducing you to the basics of the night sky and the celestial sphere. The second one 'What's to Be Seen in the Night Sky?' is describing what is at reach of the casual observers in the night sky!

What's the Night Sky?
What's to Be Seen in the Night Sky?

What's the Night Sky?

Some basic concepts about how all that works!

The Celestial Sphere The Earth is Revolving on Itself What the Stars are?	The Concept of Seasons in Terms of the Night Sky

The Celestial Sphere

any star, at night, seem affixed unto a sphere which seem to surround the Earth, which is called the celestial sphere. picture site 'Amateur Astronomy'

You know that the Earth, is just hanging -and moving- in the solar system, around the Sun! This means that we're hovering in the void of space, as far as our relationship to the night sky is concerned

Due to that position, all the stars of the night sky seem to be affixed on a sphere surrounding us, and at a same distance. Just look the sky at night and you can't tell that any star seems nearer to us than any other. All appear like dots of light, on the ultramarine blue background of the night!

This sphere which seems to surround us is just called the celestial sphere. And where do all those stars belong, could you ask? Well, they do are part of the Milky Way Galaxy, simply! With our Sun, the Earth -and us- are just part of a gigantic set of stars, which is called a 'galaxy'. A galaxy is a group of hundreds of billion stars and such popular pictures like the Pinwheel, or the Andromeda galaxies, have well popularized such those objects of the Universe. Like said, the Earth, with the Sun and the solar system, is just one of those billion stars in one of those galaxies, which we call our own, the Milky Way Galaxy that is. Should the Sun be the size of the dot of an 'i' on this page, the Milky Way would stretch from Los Angeles to New-York! All those stars we see in the night, are just a part of all those billion stars. This mostly mean, on another hand, that we see just the stars relatively nearest to us, as the rest is just seen under those veils of faint and indistinct luminosity which we call the Milky Way. As we are inside the Galaxy, we can't see it under its form of a pinwheel, but, on the one hand, we see it, when looking edge-on, either side of us, under the form of the Milky Way (it's the Milky Way Galaxy seen edge-on), and of the rest of the starry sky (it's the Milky Way Galaxy seen through)!

As far as the concept of Earth's hemispheres is concerned, the description of the celestial sphere remains the same. The only difference, as you will see, stands in that the dwellers of the southern hemisphere are allowed for the southernmost parts of it, compared to the northerners, as the inhabitants of the tropical regions are treated with views of both the parts of the celestial sphere

The Earth Revolving on Itself

You know, on another hand, that the Earth is revolving about itself each 24 hours. This determines the day, and the night. This, too, determines the apparent motion of the celestial bodies in our skies: during the day, you'll be able to see the Sun rising East, climbing into the sky until about midday, and then descent back to the West, to the horizon, and set. The same is true, albeit less obvious for the night sky. Should you stay a sufficient time under the night sky, you would see how any part of the sky is rising East, reaching its highest southwards, and then get down to the horizon, West, and set there. That motion occurs at a rate of 15° each one hour!

due to the rotation of the Earth about istself, any celestial body, the stars included seems to rise East and to set West, as, due to the Earth's axis tilt, all the celestial sphere seems to rotate about the Polaris. picture site 'Amateur Astronomy'

More specifically, as the Earth's axis, the imaginary line joining the south and north poles is tilted (by some 23.5°), all the celestial sphere seems to be axed unto the famed Polaris, that star which points to the North, in the northern hemisphere, and revolve about it!

As far as your position at Earth is concerned, in terms of latitude, the concept remains the same. The only difference is related to that, at the tropics, the Sun mostly rises due East and sets due West, arching over the zenith, as, in the southern hemisphere, you will be able to see how the Sun, there, is journeying, from the East to the West, into the northern part of their sky (at noon, that is, the Sun is seen North). At night, at the tropics, the motion of the Earth is having the sky moving straight up from the East to the zenith and then West, as, in the southern hemisphere, the sky, when facing South, is seen, just like in the North, revolving aroung the southern celestial pole (they don't have there however the equivalent of the Polaris to mark that pole, and the stars are seen rising at your left (East), getting elevated, and then setting at your right (West)

What the Stars are?

Stars are nothing else than just suns like our Sun! At the sole exception that, on the one hand, they are situated at much far distances than the Sun, and that, on the other hand, they are not necessarily of the same size than it, some being much larger, or some smaller. As an exemple, our Sun is located some 93,000,000 miles (150,000,000 kilometers) from us as nearest stars from us are located at about 5 light-years, five times 5.9 trillion miles (9,5 trillion km) that is! The sole fact that the astronomers are using another scale to render such distances is enough to show those enormous distances separating us from the stars! As far as their size is concerned, some stars may reach as far as 220 times our Sun' radius. Such a star, like Betelgeuse thus has a diameter of 186 million miles (300 million km). If placed at the place of our Sun, that star would reach far beyond the orbit of Mars

The Concept of Seasons in Terms of the Night Sky

Another concept, at last, is to be take in consideration as far as the night sky is concerned. The Earth is performing an orbit around the Sun, which lasts one year. At each of the four defining moments of this orbit (which, technically, are the official, astronomical beginnings of the four seasons, the winter and summer solstices, and the spring and fall equinoxes, namely), we on the Earth, at night, we are looking at a different part of the celestial sphere, like illustrated on the diagram here! This leads to that, in terms of observation of the night sky, it's customary to speak about 'seasonal skies'. This means that, at each season, a part of the sky only is mainly seen at that epoch, with its distinctive constellations and features! Thus, during this summer, you'll mainly see such or such constellations and parts of interest of the sky. In fall, should you keep into your interest into the hobby, you would be able to see the fall constellations and sky. Then the winter ones. And, at last, the spring constellations and sky features before, eventually, returning again to summer. The diagram assumes that we would be looking South, at about 10:30 p.m. local time (as a theoretical view related to the diagram is that, in fact, it would be midnight at our observation position, looking away from the Sun)

the Earth, on its orbit around the Sun, makes that, at each season, we may reach a part of the sky only, defining 'seasonal skies'. picture site 'Amateur Astronomy'

As far as you position related to the Earth's hemisphere is concerned, those seasonal skies remain a fact, with each season at the tropics or South, having some pecular regions of the sky proeminent. Another consideration, further, is that the constellations of the northern celestial sphere are shifting the more you go South, through the Equator, eventually being seen upside down in the southern hemisphere. The seasons, of course, are reverted South, with the southern winter being the northern summer, etc.

What is to Be Seen in the Night Sky?

What can you expect to see in the night sky?

How to See? The Constellations Planets	The Moon ... And More!

How to See?

The most obvious question is: how to observe the night sky? The answer is simple: first, naked-eye, simply! This is the best way to make you débuts into the night sky. Instruments come in second only and mostly if you keep being interested into the hobby. Barely you'll find useful too binoculars, or even a spotting scope (one of the type which is sold for terrestrial -and not astronomical, basically- observations, like birds or landscapes). Those will allow you to gain access to some pecular regions of interest, for example. Beware, as far as the use of a spotting scope is concerned, not to misuse the mounting system and tripod of it as they may not necessarily allow to fields located near the zenith, for example

As far as the naked-eye observation is concerned, be aware of the following things! First, put to profit the fact that you're mostly are, during the holidays, outside of a large city. Thus, beside the fact that the skies will be more dark than the ones you could find there, this means too that your observing horizon won't be hindered with varied buildings and obstructions! The best possible naked-eye observation location is a free, 360° horizon. If not, just adapt to the environment, of course. The most important tip, in any case, is not to be hindered by any unwanted source of light! In case of some sources of light being close, just find the appropriate angle which will elude them

Another consideration, in terms of observing the sky, is that your eyes are working in such a way that the longer you'll get into the obscurity, the more stars and details in the sky you'll be able to see. The best, so, is that, once engaged into an observational session, avoid to expose yourself back to any source of light, as you would loose the benefit of that your eyes became adapted to the darkness (should you need a flashlight, for example, just know that the amateur astronomers have a trick to avoid that question: they just use some red filter atop the flashlight (either a true filter or a bulb they painted red and use for the occasion)). Should you already have a astronomy software on a laptop and want to use the latter, most of such softwares have a function turning to red the luminosity of the laptop. In any case, thus, carefully plan the observation session. Make some prints of our charts and somme summaries of our tutorials, for example, and allow yourself to the trick of a red-lighting flashlight (even, maybe with some red-tainted translucid paper or plastic foil, for example). That's of importance!

Then, make yourself comfortable while observing. You may observe standing, or sitting on a chair or an armchair, or lying, at your convenience. Take the appropriate measures against mosquitoes, for example, or, too, dress appropriately (as the night, in some countries, may be cooler than during the day, for example)

A last thing too, about security! Should you decide to go to some dark place outside of your vacation location, for example, to have a better horizon, just think in terms of safety first. Dark places, reasonably, are not the safer places around!

The Constellations

The starry night is not a vain expression! Any night, the sky is peppered with stars! In fact, all in all and for the whole of the sky, you would be able, naked-eye, to see 5026 stars

Due to that stars are far enough to be seen seemingly at the same distance from us, they are mostly differentiated, in our night sky, through their luminosity. The apparent closenesses, or grouping between them, of various numbers of stars was readily observed by all the civilizations of the world, which led to that most of them attributed names and/or significances to those groupings. Progressively, those groupings and closenesses eventually came to be rationalized, and perpetuated along. Such closenesses and groupings of stars, seen like figures, are called 'constellations'

constellations are defined, at the same time, like figures resulting from the closenesses of some stars, and like all the stars enclosed into some boundaries. Constellations seen here are, from left to right, Hercules, the Heroe, Corona Borealis, the Northern Crown, and Bootes, the Herdsman. picture with Stellarium

The constellations today are still extent and the ones which are drawn on any sky chart are largely due to Babylonians and Greeks for the constellations themselves, as the star names, on the other hand, are mostly due to Arabs. Definitive constellations boundaries were fixed in 1930 by the International Astronomical Union (IAU) as the number of constellations was fixed at 88. A base to today constellations are the famous 48 constellations which were recensed by the Greek astronomer Ptolemy

Thus, the whole sky is organized into those constellations, both determining a series of bonds between stars which are close together, and each constellation having boundaries. Leo, the Lion, Andromeda, Andromeda, or Cygnus, the Swan are constellations. The astronomers further are referring to 'asterisms'. A asterism is a part only of a constellation which presents a striking and unmistakable figure. Such famed asterisms are, for example, the Leo's Sickle (part of constellation Leo) or the Great Square of Pegasus (part of Pegasus, the Winged Horse). You may note that the famed Great Dipper, which most probably is the most known of the constellations to any casual amateur of the night sky, is not, in fact, a constellation. It's an asterism inside the broader figure of Ursa Major, the Great Bear!

The Anglo-Saxon practice is that the constellations' names are their name in Latin, followed by the translation of it in English. Thus Cygnus, the Swan, Hercules, the Heroe, Leo, the Lion, or Draco, the Dragon, for example

As far as the stars are concerned, the most bright of them bear names. Those names, generally, are related to various cultures through which these names were given. Oldest are Greek, like 'Antares', some are due to the ancient Rome, like 'Regulus', as the greatest number of stars' names are derived from names Arab astronomers used in the Middle Ages, based on their peoples' use (like Altair, or Deneb, for example)

Some more technique, at last! Let's say some words about the 'magnitude' of stars! The magnitude of stars is a set of scale which allows to say what the luminosity of a star is. That scale of luminosity dates back to the Greeks, when stars had been divided into six classes. The brightest stars were in the first class and the faintest in the 6th. Each class of magnitude represents a star's brightness 2.512 times fainter than the previous. I.e. a star of the 3rd magnitude is 2.5 times less bright than a star of the 2nd magnitude, as it is 2.5 times brighter than a star of the 4th magnitude. The magnitude scale starts at 0. Stars which are brighter than the class 1 are termed negative (Sirius, for example, the brightest star in Northern hemisphere had a magnitude of -1.5). At night, naked-eye, you're able to reach down to the 6th magnitude stars and celestial objects only. To get to the stars below, you'll need an instrument

Planets

Planets are the other objects you may encounter in the night sky! Those are just the 8 other planets which compose the solar system with our Earth! Of them, on the other hand, 5 only may be seen naked-eye, Mercury, Venus, Mars, Jupiter and Saturn namely, as Uranus, Neptune, and Pluto are too dim to be spotted naked-eye

As some planets are located between us and the Sun, like Mercury and Venus, those can't be seen at another moment than the twilight in the evening, or at dawn in the morning. Mercury and Venus, thus, only are seen like either an evening, or a morning star, providing for fine views in the last gleamings after the Sun set, or before it rises. Should you see a bright star few before the Sun set, or keeping seeable as the lights of dawn are rising, be sure it's about mostly Venus (if deemer and low, it's Mercury). The other planets are situated beyond us. Thus, their position in the sky depends of where they are on their orbit, and relatively to the Earth's own position on its. This is true, thus, for Mars, Jupiter, and Saturn

The way, naked-eye, to discriminate a planet from a star is easy, as stars do glitter intermittently, and planets don't. Should you spot a star the light of which mostly is steady, it's likely a planet. To ascertain to what planets are observable this summer, just check the ephemerides at our site 'Amateur Astronomy'. Due to that all the planets in our solar system are orbiting mostly in the same plane, the planets, in the night sky, are always seen along what is called the zodiac. The zodiac is a 16 degree-wide band of sky where, in perspective, the planets are seen. The constellations located along that band are the famed 'zodiacal constellations', numbering at 12 and the concept of which is unluckily used too for astrological purposes

Any planet in the sky will just modify the shape of the constellation in which it's located when you observe. The only drawback, in terms of any planet present in the sky, is that you won't be able to see some of it, as any observation of a planet needs a minimum of about a magnification of x45 (which may be just at the limit of a spotting scope however). Planets, in term of amateur astronomy, are fine object to see in the dedicated instruments -the refractors or reflectors- the amateurs are using, each one with its beauties. Venus and Mercury are strikingly displaying phases similar to those of the Moon. Mars is the famed red planet (and somewhat a difficult object, needing high magnification powers) as Jupiter is an easy, round and striped object, with its 4 main satellites seen moving around it in matter of hours, and that Saturn displays its famed ring!

As far as the observation's location is concerned, you will note that, in the northern hemisphere, the globes of the planets are seen with their North to the top, and their South to their bottom. In the equatorial regions and the tropics, the planets are seen lying on their side, with their polar axis seen parallel to the horizon. Saturn's ring, thus, is just seen plane to the horizon! In the southern hemisphere, further, the planets are just see upside down, with their South at the top of their globe, and their North at the bottom!

The Moon

The Moon is Earth's moon! It's located at just 239,000 miles (380,000 kilometeres) from us. The Moon, on another hand, in the case of an observing session, maybe a hindrance, the nearest it is from the full Moon, at its luminosity surely will wash away the light of the dimmest stars. So, check what the Moon is for a given day! Due to its regular orbit around the Earth and its relative position to the Earth and the Sun, the Moon, thus, is performing, on about a month's duration, its same sequence of phases. The Moon, on the other hand, due to its revolution period around the Earth equaling its rotation period on itself, always had the same side of it facing Earth. The far side of the Moon remained unknown until the space age!

click to Moon's phases

In the northern hemisphere, just after the new moon, the first crescent Moon appears West and day after day, it gets distant from the Sun at the same time is increases in size. At first quarter Moon appears full South when Sun sets. The quarter Moon become waxing gibbous and it appears more East each day. When Moon reaches full, it's rising East just when Sun is setting West. Moon then sets in turn about 12 hours later that is by next morning. Waning gibbous Moon rises later each day until it reaches last quarter. Moon then rises at midnight and sets about midday. The last crescent completes the cycle as it rises less and less early before Sun. Generally, each night, the Moon is moving by about 12.5° relative to the background stars where it was located the previous day. In terms of the observer's location, what has been said about the planets' aspect at the tropics or the southern hemisphere is true for the Moon. At the tropics and the equator, the Moon's globe is seen lying on its side, as, in the southern hemisphere, the Moon is seen upside down, with the South seen up, and the North at the bottom! Another remarkable fact about the Moon is the southern hemisphere is thus, that the crescent aspect is reverted compared to the northern hemisphere, along with the monthly apparent journey of the Moon into the sky: the Moon phases are unfolding, in the sky, from the northwest to the northeast, as, for example, the horns of the first crescent Moon are turned to the North, instead of the South in the northern hemisphere

In terms of naked-eye observation, Moon, does not offer much, except for the unfolding of the phases and this famed, remarkable faint light which is displayed during that Moon is a crescent or a quarter. This is called the 'ashen light', the 'ashen glow', or the 'Earthshine", and it is a fine show. Moon's part which is still in night is lit by "earthshine". For an observer located on the Moon it would be night and Earth would be shortly after "Full Earth", ornating their skies. The ashen glow is seen too at last quarter Moon when last crescent is rising on eastern horizon. A popular expression is terming the ashen glow "the old Moon in the New Moon's arms"

Binoculars or a spotting scope may obviously help to the Moon! With even small magnifications you'll be able to already better spot the main Moon relief features. You'll see how the Moon's terrain is parting between bright, old, mountaneous regions, flat, dark, large plains, and as it's variously spotted with varied craters! Another observation will be too that the relief features are more accurately seen along what is called the 'terminator', that line which defines in what phase the Moon currently is (it's where the surface of the Moon divides into the part which is lit by the Sun, and the part which is not). Moon was reached by man during the 1960's and the beginning of the 1970's by the Apollo missions as the USA are aiming to bring man back to Moon about 2020 now

... And More!

What else to be seen in the night sky? More still, with the Milky Way, shooting stars, or more!

Another striking aspect of the sky which is at reach during the summer nights is the Milky Way! The Milky Way is that vast band of faintly glowing draperies which is seen stretching into the night sky, mostly stretching from a horizon to the other. That's a great view! What the Milky Way is, in fact? The Milky Way -and that's interesting- is just our Milky Way Galaxy as seen edge-on and from the interior! We, with the Earth, the Sun, and the solar system, are part of one of those spinwheel galaxies which have been popularized by such pictures of the Andromeda galaxy or other remarkable such objects. As we are able to watch the spiral structure of those galaxies for the galaxies to which we don't belong, we can't see the one of our Galaxy due to that we are inside it. This provides us with the view of the Milky Way. From the inner of the Galaxy, when we're looking in the sky towards the plane of it, either side of our position in there, we are are seeing the most populated and densely packed regions of it. That's the Milky Way. And when we look towards the directions perpendicular to the plane, we see a more loosely populated sky (and technically, we can reach, through those less dense regions, to the outside of our Galaxy, to the other galaxies spread into the vastness of the Universe, and to the far reaches of the latter! During summer, in the northern hemisphere, the Milky Way is stretching from due South to the North. That's a remarkable show to imagine that we are seeing our spiral, pinwheel, Milky Way Galaxy edge-on, the plane of the arms that is. All those faintly glowing draperies are just those billions of stars located there and so numerous, and so much far from us that we can't individualize them anymore! We just see them under the form of that faint glow arching over the sky! Dark lanes of dust clouds are dimming or blocking too the Milky Way's faint glow. Most prominent dark lane stretches from the constellations Cygnus to Sagittarius and is often called the Great Rift, sometimes the Dark Rift

our Milky Way Galaxy is of the pinwheel, spiral type, with arms spiraling from a central bulge. The arms and bulge, as seen edge-on and from the interior, yield the Milky Way arching in our night skies! picture site 'Amateur Astronomy'

The plain view of the Milky Way, of course, is reserved to those who have dark skies enough for the view, due to that any important source of light will wash down its luminosity however. Another show of interest, as related to the Milky Way, during summer, is that, due South, in the constellation Sagittarius, the Archer, we have the view of the center of the Milky Way Galaxy! It's there that, on the one hand, the bulge of old, yellowish stars of the pinwheel is located, and, on the other hand, that the supermassive black hole of the Galaxy is lurking! Like any other galaxy in the Universe, like the astronomers know now, our Milky Way Galaxy is harbouring a large, monstruous black hole in its center. Black holes are the places of the most high density in the Universe, places of the highest gravitational pull. From such a place, nothing, not even the light, which is the object with the highest speed in the Universe, can escape. The origin of why galaxies have such objects in their center is still badly known. Galactic black holes are still active, as they are mostly usually 'dormant' and quiet however. But, they may -about once every 10,000 years- swallow a passing star. When it comes to assumptions, black holes are believed to be the place of interconnection with places where the laws of physics might be completely different, or where it might be possible to travel in time. One thing is certain however. Should you venture for a long space journey, never approach a black hole of any kind. You would never be back!

A famed show into the night are too the shooting stars. Along the year, amateur observers may observe from time to time a luminous strike in the sky. This is a shooting star. Most of shooting stars are sporadic and about 6 per hour may be seen each night. Shooting stars are pieces of material, averaging in size from sand grain to pebbles, entering in the Earth's atmosphere, and burning due to friction. At some periods of the year however, shooting stars become more numerous. Up to 60 e.g. may be seen per hour then. These so-called meteor showers are due to meteorids streams orbiting the Sun. These swarms are leftovers from comets. Shooting stars perspectively appear to come from a same point of space

Table of the Most Usual Meteor Showers

Name	Dates	Usual date(s) of maximum	Hourly rate (ZHR; gives an idea of the intensity of the shower)	Radiant (the apparent point in the sky where the meteors seem to originate)
Quadrantids	Jan. 1-5	Jan. 2-3	120	230 +49
Lyrids	Apr. 16-25	Apr. 21-22	15-18	271 +34
Eta Aquarids	Apr. 19-May 28	May 5-6	60	338 -01
Southern Delta Aquarids	Jul. 12-Aug. 19	Jul. 27-28	20	339 -16
Perseids	Jul. 17-Aug. 24	Aug. 11-12	100-110	046 +58
Alpha Aurigids	Aug. 25-Sept. 5-8	Sept. 1	7-10	084 +42
Orionids	Oct. 2-Nov. 7	Oct. 21-22	20-23	095 +16
Leonids	Nov. 14-Nov. 21	Nov. 17-19	ability to storm	153 +22
Puppid-Velids	Dec. 1-Dec. 15	about Dec. 7	10	123 -45
Geminids	Dec. 7-Dec. 17	Dec. 13-14	120	112 +33
Ursids	Dec. 17-Dec. 26	Dec. 22-23	10	217 +76

More objects, or phenomenons may be seen in the sky, as they may be rare, or they need an instrument or some too specific techniques. Such objects are of the sort of the northern lights (which are not observable in summer due to the midnight sun), a Sun or Moon eclipse, and faint objects like the star clusters, nebulae or galaxies. The Sun in itself is observable only through dedicated, safe techniques, as its observation without those techniques is extremely dangerous to the eyes, up to a definitive blindness (see more below)

->Feeling interested by the hobby? See more subjects, and detailed studies, at the site 'Amateur Astronomy'!