Short Tours of the Night Sky
On Day 2, you learned how it moves from day to day and year to year and where to find the celestial poles and equator and the ecliptic. Today, you’ll learn what’s “on” the celestial sphere… the bright stars and constellations you can see each season from the northern and southern hemisphere.
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Learning the sky is really no different than learning the streets of a new city or town. A map is the best way to orient yourself. Of course, as you start out, you don’t need a detailed map with elevations and minute detail of every house and tree down to the square meter. You just need a basic map showing the major streets and landmarks, and how to get from place to place.
So it is with star charts. Many advanced amateur astronomers use highly detailed star atlases that have thousand of stars and deep-sky objects, along with markings of coordinates down to the degree. When you’re just starting out, you don’t need that. You just need a good, basic star chart that shows you where to find the bright stars and main constellations at a particular time and place.
Today, that’s what you’ll get… four star charts for each hemisphere to show you what you can see in each season. But first, a word about how to read these charts…
How To Read A Star Chart
The charts below show you what you can see from the northern and southern hemispheres at a latitude of 40 degrees north and 35 degrees south, respectively, at 9 p.m. on April 15, July 15, October 15, and January 15.
As you learned on Day 2, because of the revolution of the Earth around the Sun, the stars appear to rise about an hour earlier every two weeks or so. So these stars maps are just as valid if you use them at 8 p.m. two weeks later on May 1, August 1, November 1, February 1. Or at 10 p.m. two weeks earlier on April 1, July 1, October 1, and January 1, and so on.
As another example, the star chart for July 15 at 9.m. will also give you the correct star positions for April 15 at 3 a.m. And at midnight on April 15, the stars will lie in positions between what is shown by the 9 p.m. charts for April 15 and July 15. So for most nights of the year, you can use one of these maps early in the evening, and another a few hours after midnight to get a fairly accurate representation of the sky.
The charts below try to represent a hemispherical sky on a flat surface. The edge of the chart represents the horizon, and the center of the chart is supposed to represent the zenith (the point directly overhead) at 40 degrees north (or 35 degrees south). East and west are reversed compared to an map of the Earth, but they will point in the right directions when you raise the map over your head.
To read a star chart, here’s what you have to do…
• Find a location that’s isolated from street and house lights. Stray light will make it harder for you to see fainter stars. Also, for the same reason, try to avoid nights with a full moon or too much haze.
• Once you go outside, give your eyes 5 or 10 minutes to become adapted to the dark. And to see the star charts, use a red LED flashlight or a white flashlight covered with red plastic. The red light will preserve the sensitivity of your eye for night viewing. (More about this on Day 5).
• Pick a direction to face, say, South, and rotate the chart so South is at the bottom. Now raise the chart overhead. The directions on the chart will now correspond to the directions in the sky.
• Don’t try to take in the whole sky at once. Choose a quarter of the map, preferably one with several bright stars or a large well-known constellation like Orion or Ursa Major (of which the Big Dipper is a part). Now, look up at the quarter of the sky that corresponds to the quarter of the map. Make a connection with what you see in the sky with what you see on the map. Take your time… it’s a little strange and overwhelming at first.
• Learn a few more stars at a time… don’t rush. Once you’ve identified a few bright stars and constellations, move from what you know to what you don’t know. Once you’ve learned most of a quarter of the sky, move to another quarter.
• Remember… while the charts are set for 9 p.m. local time, they are still useful for an hour or two on either side. The stars will appear in about the same position, except for the stars near the horizon. After 3 hours, the stars will have turned 1/8 of the way around the sky. And after 6 hours, they will have turned 1/4 of the way around the sky.
• If you see an out-of-place star near the ecliptic (and in one of the constellations of the zodiac), it’s almost certainly a planet. Since the planets move around in the sky almost daily, you will need to consult an almanac or website to figure out which planet you are seeing. Sky and Telescope is and especially good place to check. We also review the positions of the planets each month here at One-Minute Astronomer.
That’s all there is to it. Well, that and a whole lot of practice. Be patient, and savor your personal discovery of each new star and constellation.
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Now, here are some star maps and mini-tours for each season to get you started, one each for observers in the northern and southern hemispheres.
The Sky from March to June
By mid-April, the bright stars of winter are setting in the west to make way for the relatively star-poor skies of spring. The constellations Orion and Canis Major are setting in the southwest. taking with them the dazzling stars Betelguese, Rigel, and Sirius. The yellow-white star Capella is still high in the western sky. And Castor and Pollux, which mark the heads of Gemini, the twins, are nearly overhead. This west and south part of the sky are still fairly rich with the the stars of the Milky Way.
Ursa Major, with its star pattern the Big Dipper, is easily visible directly overhead. The two front stars of the bowl of the Dipper point northward to the north star Polaris. This star is less than a degree from the north celestial pole. Polaris is also the tip of the tail of the constellation Ursa Minor (also known as the Little Dipper). East of the Dipper lies the bright yellow-orange star Arcturus in the constellation Bootes. And northeast of that, you’ll see the unmistakeable sight of Corona Borealis, the northern crown.
Just south of the zenith, following the arc of the ecliptic, you will see several constellations of the zodiac. Leo is overhead. It’s mane and head look like a large “reverse question mark” and its body and legs point eastward. Further east, look for the constellation Virgo with its bright blue-white star Spica glittering in lower in the southeast. West of Leo lies the fairly dim constellation of Cancer and the brighter Gemini. The V-shape of Taurus, the Bull, is setting in the west along with its bright red star Aldebaran.
In the northern hemisphere at this time of year, you are looking out of the plane of the galaxy into the depths of intergalactic space. That’s why you see few bright foregrounds stars in this part of the sky. But a telescope will reveal hundreds of distant galaxies in this region of the sky, especially the galaxies of the Virgo galaxy cluster, which lies just southeast of Denebola in Leo, and under the handle of the Dipper in Canes Venatici.
The sky on April 15 at 9 p.m. at 40 degrees north latitude (click to enlarge)
In the early autumn sky of the southern hemisphere, the dazzling stars of the Milky Way are visible in a band that runs from the southeast to the west. The winter constellations of Orion, Canis Major, and Gemini are setting in the western sky, while the fine sights of Puppis, Vela, and Carina lie overhead. Just southwest of the zenith, you’ll see the bright stars Canopus and Sirius. And east of the constellation Carina, you’ll see the famed (but small) constellation of Crux, the Southern Cross, and Centaurus with its bright star Rigel Kent.
South of the band of the Milky Way lie the two Magellanic Clouds, two dwarf galaxies some 150,000 light years from our own. Glimmering in the southeast, just above the horizon at this hour, you will see the head of the constellation Eridanus, the River, which winds some 100 degrees from the foot of Orion, up past the western horizon, and back again.
The sky towards the north contains only three bright stars: Arcturus, Spica, and Regulus in the constellations Bootes, Virgo, and Leo, respectively. In this direction, you are looking out of the plane of the galaxy into the depths of intergalactic space. That’s why you see few bright foregrounds stars in this part of the sky. But a telescope will reveal hundreds of distant galaxies in this region of the sky, especially the galaxies of the Virgo galaxy cluster, which lies just southeast of Denebola in Leo.
Below Virgo lies the quadrilateral of Corvus, the Crow. In the southeast, you will find the striking sight of Scorpius rising, with its claws pointing northeast and its menacing stinger, rich with clouds of stars and star clusters, hanging in the southeast.
The sky on April 15 at 9 p.m. at 35 degrees south latitude (click to enlarge)
The Sky From June to September
By 9 p.m. on July 15, the stars have moved westward by 90 degrees. Leo, which was high in the spring sky, is now setting in the west. The Big and Little Dippers have made a quarter turn around Polaris compared to their position at the same time on April 15. In between the Big Dipper and Little Dipper lies the long dim constellation Draco, the Dragon.
But new constellations have risen in the east, bringing into to view the bright stars of the summer sky. High overhead you will see the dazzling blue-white star Vega in the small constellation Lyra. The constellation Cygnus and its bright star Deneb lie northeast of Vega. Cygnus is supposed to represent a flying swan, but its most easily recognized as its informal name, the Northern Cross. Further to the southeast you will see the bright star Altair in the eye of the constellation Aquila, the eagle. The stars Vega, Deneb, and Altair mark what’s known as the “Summer Triangle”. You can follow the triangle on its slow path westward each night well into late autumn. Next to Vega, almost directly overhead, you’ll see a “keystone”-shaped group of four stars which marks the body of the constellation Hercules.
Look also for the tiny constellations Delphinus and Sagitta. They look very much like the dolphin and arrow after which they are named.
Perhaps the finest celestial sights of the northern summer sky lie near the southern horizon. That’s where you’ll find the star clouds of the Milky Way in the constellations Scorpius and Sagittarius. Scorpius is supposed to represent a celestial scorpion, and it does so convincingly, with its claws pointing northward and its stinger southward. Antares is the twinkling bright red star in the heart of the Scorpion. The Milky Way grows thickest in the southeast in the teapot-shaped constellation Sagittarius. This constellation is thick with open and globular star clusters and diffuse and planetary nebula. Towards Sagittarius, lies the center of our galaxy, which is why the star clouds of the Milky Way are so thick in this part of the sky.
The sky on July 15 at 9 p.m. at 40 degrees north latitude (click to enlarge)
While the Milky Way in the northern hemisphere is spectacular, the view from the southern hemisphere this time of year is even better. Sagittarius, Scorpius, and Scutum are directly overhead, which makes it easier to see the nearby celestial treasures (see above). If you can, sweep this area with binoculars to get a glimpse of the riches of this region.
Crux, Centaurus, and the other main constellations of southern autumn are moving westwards towards the horizon, as are Virgo and Corvus. They’re replaced in the east by Aquarius, Capricorn, Piscis Austrinus and its bright star Fomalhaut, and the deep southern constellations of Tucana and Phoenix. Try to see the globular star cluster 47 Tucanae, which looks like a fuzzy star to the unaided eye.
And to the north looms the great pentagonal shape of Ophiuchus and the northern constellations Hercules, Lyra with its bright blue-white star Vega, and Corona Borealis.
The sky on July 15 at 9 p.m. at 35 degrees south latitude (click to enlarge)
The Sky From September to December
The Summer Triangle moves past the meridian and works its way westward during the northern autumn. The rich band of the Milky Way in the constellation Sagittarius disappears into the southwest. Near the southern horizon, if you have an unobstructed view, you’ll see the star Fomalhaut in the constellation Piscis Austrinus.
The zodiacal constellations at this time of year include, from west to east, Sagittarius, the dim constellations Capricorn, Aquarius, Pisces, Aries, and the brighter Taurus. Rising in the northeast sky, you’ll see the star-rich constellation Perseus and the W-shaped constellation Cassiopeia, which reveal many fine star clusters to an observer with binoculars or a telescope. When you look towards Perseus, you look at an arm of the Milky Way galaxy that lies in the opposite direction from Sagittarius.
Perhaps the most conspicuous constellation of a northern autumn is Pegasus, the winged horse of Greek legend. The body of Pegasus comprises the “Great Square”, which lies just southeast of the zenith. And attached to Pegasus is the constellation Andromeda, which harbors the nearest major galaxy to our own. The Andromeda Galaxy can be see easily with the unaided eye in dark sky as a faint fuzzy patch of light between the star Almaak and the constellation Cassiopeia. But don’t underestimate this fuzzy patch… it’s actually a galaxy like our own Milky Way, though somewhat larger, with some 200 billion stars. The light from this galaxy, which you can see for yourself, was has been traveling towards your eye for some 2 million years.
Look also in the east for the rising Pleiades star cluster, which lies within the constellation Taurus. Its appearance marks the coming of winter in the northern hemisphere.
The sky on October 15 at 9 p.m. at 40 degrees north latitude (click to enlarge)
Because you’re looking out of the plane of the Milky Way into deep intergalactic space at this time of year, the sky of the southern hemisphere has relatively few bright foreground stars. The eastern and northeastern sky is nearly deserted of bright stars. But with a telescope, there are many faint galaxies visible in the faint overhead constellations Grus, Sculptor, and Fornax.
The bright star Fomalhaut sits almost at the zenith, with Achernar just southeast. Tucana, with its splendid globular cluster 47 Tucanae can be found nearby. The remnants of the spring and summer Milky Way, including the constellations Crux and Carina, lie low on the southern horizon. Scorpius sets claws-first into the southwestern horizon. And the bright star Canopus lies in the southeast sky in Carina.
In the north, you’ll see the Great Square of Pegasus and the attached constellation Andromeda. Cygnus and little Delphinus and Sagitta lie off to the northwest. The winding constellation Eridanus winds nearly overhead from the eastern horizon, leading the constellations of a southern summer into the eastern sky. Pisces and its pentagonal head lies just above Pegasus. Cetus, the sea monster, looms in the east between Pisces and Eridanus.
The sky on October 15 at 9 p.m. at 35 degrees south latitude (click to enlarge)
The Sky From December to March
Pegasus, Andromeda, and Cetus sink into the west by January, while the stars of spring begin their rise in the east late in the evening. In between lie the grand constellations of winter: Orion, Taurus, Auriga, Perseus, Cassiopeia, Gemini, and Canis Major. Because these constellations lie along the plane of the Milky Way, they are rich with stars, nebulae, and star clusters.
Look overhead to find a grand G-shaped collection of stars: Capella, Castor and Pollux, Procyon, Sirius, Rigel, Aldebaran, and Betelgeuese. These stars are a spectacular sight on a dark winter night. Orion, the hunter, is the feature constellation of winter in both hemispheres, and makes a good base of operations to find other constellations. South and east of Orion lie his hunting dogs Canis Major and Canis Minor. The former constellation hosts the brightest star in the sky, Sirius, which shines unmistakably in the southeast.
To the north and west of Orion lies the V-shaped constellation Taurus. The bright star Aldebaran marks the eye of the bull. Northwest of Orion lies Gemini, the twins, with their feet dipped in the rich star fields of the winter Milky Way. And directly above Orion you’ll find the constellation Auriga, also set in the Milky Way. Its bright yellow-white star Capella twinkles almost directly overhead.
The Dipper has turned into the northeast, and opposite the Dipper from Polaris is the W-shaped constellation Cassiopeia. Beside Cassiopeia lies Perseus. The outer arm of the Milky Way runs through these constellations, so they are rich with stars.
The sky on January 15 at 9 p.m. at 40 degrees north latitude (click to enlarge)
The bright G-shaped group of stars visible from the northern hemisphere is also prominent from southern latitudes. But southerners will also see the bright white supergiant star Canopus almost directly overhead.
The band of the Milky Way arcs from the southeast to the northwest, starting from the Southern Cross, extending through Carina and Puppis, through Canis Major and Orion, and extending over the horizon to the northern constellations Auriga and Perseus.
The Large Magellanic Cloud lies overhead in the constellation Dorado, and the Small Magellanic Cloud sits just to the southwest in Tucana.
Southerners also see the full length of the winding constellation Eridanus, the river. The constellation starts near the bright star Rigel and winds west and south for 100 degrees, ending at Achernar, just southwest of the zenith.
The sky on January 15 at 9 p.m. at 35 degrees south latitude (click to enlarge)