Monday, July 29, 2024

 

Seven Wonders of the Night Sky

Visible to the Naked Eye

 

“When life gets too overwhelming, just look up at the night sky and lose yourself for a while.”

– Rachel Wolchin

“I see the night sky as a personal friend, and it’s always been there for me. I’m out there all the time, looking up at the night sky. It is really something that I’m close to, and a deeply ingrained part of my life.”

David H Levy
Astronomer

[A rich part of the dark night sky showing objects of the sixth magnitude and brighter, generated with the Starry Night Pro Plus 8 software package on Windows 10]

In tune with the choice of seven wonders in different categories of objects on the Earth’s surface, this article extends the idea to another category – the myriad wonders of the night sky above, from among those visible to the naked eye.


Prelude

The impetus for writing this article came from a news item reporting how an Egyptian adventurer succeeded in seeing all seven (manmade) wonders of the world that are spread across the globe and pose a huge logistic challenge, in less than seven days using only public transport services, thereby setting a new world record. He had started from the Great Wall of China, travelled westward across the continents, and finished up with the Chichen Itza in Mexico.  In a spontaneous and impish reaction to this I posted the message; “I have also set a record of sorts - taking six decades to achieve the same fete!” This was an intended reference to my last blog article (see here) in which I had narrated how I had completed a run of all the seven modern wonders of the world, starting with the Taj Mahal way back in 1963, and ending up with Chichen Itza in April this year.  

At this juncture, Ajay Talwar, the doyen of Indian Amateur Astronomy and Astrophotography, interjected: “What would be the seven wonders of the night sky?”  He also remarked that from his point of view such a list would include the Zodiacal Light, as well as Gegenschein, both easily visible at the Hanle Dark Sky Reserve (see here) where I had first met him last October.  This set a train of thought among a few of the participants of the HDSR Party, and I joined in with the observation that my list was sure to include the Pleiades, the breathtakingly beautiful star cluster of ‘seven sisters’.  But nobody came up with a complete list of seven and the matter went into limbo for some time. I am resurrecting it with this article in which I come up with my full list of seven wonders of the night sky, all readily visible to the unaided eye, with a brief illustrated write-up on each of them, and invite readers to react with their own list of seven wonders.

The Criteria

As regards the choice of objects for the list of seven wonders, I laid down for myself the following criteria:

1.    They should not require any optical aid for viewing.

2.    They should be visible easily to any astronomy enthusiast on a clear dark sky, late in the evening or early in the morning.

3.    At least a few of them should be observable at some time of the day, regardless of the season.

4.    The observer should ideally be located in the low northern equatorial latitudes.

5.    Transient events like the passage of a comet are to be excluded.

Sadly, these criteria exclude Ajay Talwar’s preference for the zodiacal light and Gegenschein which are not easily observable under normal conditions.  

The Short List  

The organizers of the ‘New 7 Wonders of the World’ worldwide poll had made a short list of 21 objects (see here) from which the final seven had to be decided by popular choice.  Following a similar modus operandi, I have identified the following 21 night-sky wonders as my short list, in alphabetical order:

1.    Alcor-Mizar star pair in the Big Dipper

2.    Algol (a variable star in the constellation Perseus)

3.    Alpha Centauri (bright star in the southern sky)

4.    Auriga constellation

5.    Big Dipper in the Ursa Major constellation*

6.    Canopus (brightest star in the southern sky)

7.    Earthshine (on a thin crescent Moon) *

8.    Meteor showers such as the Perseids

9.    Milky Way patch in constellation Sagittarius*

10. Omega Centauri (globular cluster in the southern sky)

11. Orion constellation and nebula M42*

12. Pleiades cluster M45*

13. Pole Star (Polaris)

14. Scorpius (a zodiacal constellation)

15. Sirius (brightest star in the night sky)

16. Southern Cross (a constellation in the southern sky) *

17. Square of the Pegasus (in the northern sky)

18. Summer triangle (formed by the stars Altair, Deneb and Vega)

19. Taurus (a zodiacal constellation)

20. Venus (the brightest object in the night sky after the Moon) *

21.  Winter Triangle (formed by the stars Betelgeuse, Sirius and Procyon)

[* Figuring in my Final List of 7]

My Seven Wonders

Polled by just one man (myself) with just one vote, here is my final list of the glorious seven wonders of the night sky, also in alphabetical order:

1.    Big Dipper (part of constellation Ursa Major)

2.    Earthshine (as seen on the unlit side of a thin crescent Moon)

3.    Milky Way patch in constellation Sagittarius

4.    Orion constellation

5.    Pleiades cluster

6.    Southern Cross constellation

7.    Venus

Needless to emphasize, this list strongly reflects my personal experience and preferences, much like any set of seven wonders in any category. The reader is welcome to come up with his/her own version, and no two versions may be identical.

I now proceed to describe briefly each of the seven wonders of my list.

1.        Big Dipper

The Big Dipper is an asterism (a pattern of stars that is not a constellation), and part of the larger constellation Ursa Major, the Great Bear. It is one of the most recognizable groupings of stars in the northern sky and consists of seven bright stars (see picture below), known in Sanskrit as Saptarshi Mandal (seven rishis).

The Big Dipper serves as a useful marker for locating other stars and constellations in the night sky.  The two stars, Dubhe and Merak, at the end of the ‘bowl’ of the Big Dipper, point to Polaris, the Pole Star. This is particularly useful in low northern latitudes for locating the Pole Star which is very nearly aligned with the Earth’s rotational axis, thereby appearing to be stationary in the sky.  The other five stars in the asterism are named Alkaid, Mizar, Alioth, Megrez and Phecda, respectively. 

Located in the handle of the Big Dipper is the ‘naked-eye double star’ system, Alcor and Mizar.  Mizar, the brighter of the two, is a second magnitude star, and Alcor is of fourth magnitude.  Under good viewing conditions, both can be seen without optical aid, appearing to be clinging together. The Alcor-Mizar pair can be used as a test of sharp eyesight, many people finding it challenging to see them separated.  Called Vasisht and Arundhati in Sanskrit, the bride and the bridegroom in Hindu wedding ceremonies are expected to be shown this pair as symbolic of a tight union between them. In actual fact, the priest performing the wedding just points his finger skyward ritually, almost always during daytime!

2.        Earthshine 

When the Moon is in a thin crescent phase in a clear sky far away from disturbing lights, one can see not only its bright sunlit part but also the rest of it, dimly visible if observed carefully (see figure above). This happens because of the light scattered off the earth’s oceans and clouds falling on the ‘dark’ portion of the Moon and illuminating it faintly.  Under the right observing conditions this is a spectacular sight, giving an eerie three-dimensional appearance to our celestial neighbor.  The best time to look for this is one or two days after a new Moon and at least an after the Sun has set completely.  Though it is not always easy to observe, unlike other objects in this list of wonders, the result is well worth the effort.  This earthshine on the lunar surface can be used to obtain an insight into the reflective properties of the Earth, called the albedo. 

3.        Milky Way in Sagittarius

On a totally clear and dark moonless night, far away from polluting lights, it is possible to observe large parts of the Milky Way, the galaxy of which we are an integral part, as a hazy irregular patch of cloudiness stretching all across the sky. This light comes from the combined glow of millions of distant stars within the galaxy’s disk. Much of the light is absorbed by intervening gases and dust, giving rise to irregular dark patches. The center of the Milky Way lies in the direction of constellation Sagittarius, and this gives rise to the brightest patch of light in this region (see picture below). Under ideal viewing conditions like the Hanle Dark Sky Reserve, it is a truly awe-inspiring sight (see here).   

[Generated with the Starry Night Pro Plus on Windows 10]

The region of the night sky adjacent to this hosts the zodiacal constellation Scorpius, which very much resembles a scorpion, true to its name, unlike most other constellations or asterisms.

4.        Orion the Hunter

[Generated with the Starry Night Pro Plus 8 on Windows 10]

When positioned nearly overhead, Orion the hunter is probably the best recognizable of all the constellations in the night sky, and its neighborhood is strewn richly with wonders of all kinds (see figure above as well as the one displayed at the beginning of this article).  It resembles the shape of a hunter with his bow drawn and ready to shoot an arrow, and with his lower body wearing a belt and a dagger. The belt has a set of three bright stars in a row, named Alnitak, Alnilam, and Mintaka. At the middle of the dagger is a diffuse nebula (M42), which is the brightest of its kind visible to the naked eye. Betelgeuse is a red supergiant star approaching the end of its life and Rigel is a blue giant star, the brightest in the constellation.  Through a pair of binoculars or a low powered telescope the nebula shows a wealth of detail that is unfortunately not visible to the naked eye. With Sirius, the brightest of all the stars in the night sky, and Procyon, another bright star in a neighboring constellation, Betelgeuse forms a large, near perfect, equilateral triangle, known famously as the winter triangle.

5.     Pleiades

Pleiades is a tight knit open star cluster, readily recognizable in the constellation Taurus (see picture below). In Greek mythology it is known as ‘seven sisters’, seven being the number of bright stars ordinarily visible in the cluster to the normal eye on a dark moonless night.  Like the Alcor-Mizar pair in the Big Dipper, this is also a test of sharp vision. Many people find it difficult to see all seven and a vision test maybe helpful in such cases. The most prominent star in the cluster is named Alcyone.  There are eight others, with the names Asterope, Celaeno, Electra, Maia, Merope, Taygete, Atlas and Pleone.  The cluster actually has over a thousand stars, all relatively young and blue, and 444 light years away from us. 

[Generated with the Starry Night Pro Plus on Windows 10]

The Pleaides, also identified as M45 in the Messier catalog, lies is a region of the sky rich in stars and star clusters, with the ‘horn of the bull’ in the Taurus constellation, and the Hyades open star cluster, both being very prominently visible in the constellation.

Through binoculars, the cluster can be seen clearly (see picture below), with a distinctively blue nebulosity caused by scattering of light from stars within the cluster by interstellar dust. 

6.     Southern Cross

The southern cross (see picture below) is a key feature of the night sky seen in the southern hemisphere, and the smallest of the 88 constellations that are formally recognized. In the northern hemisphere it lies very low in the south, and is best seen at its highest altitude, well above the horizon.  Nearby is the well-known Centaurus constellation (not shown), with Alpha Centauri being one of the brightest and nearest stars.

The four brightest stars of the constellation form a distinctive cross shape, with a fifth star located off the cross. The formation was a great navigational aid in the southern hemisphere during olden times. The rise of this constellation above the southeastern horizon is preceded by the appearance of a similar looking formation, but with fainter stars and a larger size, often mistaken for the true southern cross, and hence called the false cross.

[Generated with the Starry Night Pro Plus on Windows 10]

7.     Venus

After the Moon, planet Venus is the brightest object in the night sky, and the most easily recognizable one, seen after sunset or before sunrise, located not too far from the Sun. Often called the morning or evening star, it is the nearest planet to us in the solar system, as also the brightest in appearance because of a dense shroud of carbon dioxide and other noxious gases enveloping the hot planet. Though it looks like a serene and heavenly object, it hides a toxic hell in its composition.

Like the Moon, Venus has phases, with a thin crescent phase when nearest to the earth. Then the sunlit surface has also the largest area. For this reason, it is also seen at its brightest.  However, the human eye is unable to see the different phases, always taking it for a bright and brilliant roundish object.   Because of its brightness and generally low altitude, Venus has often been reported as a ‘flying saucer’ by novice and inexperienced viewers of the sky. 

The picture below, taken by Ernie Mastroianni on the morning of 28th October 2015 an hour before sunrise, shows a brilliant Venus (magnitude -4.6) at the top, with Mars and Jupiter (magnitude -1.8) paired up to its lower left. The picture also shows Mercury, the bright object near the horizon.

Postscript

Other members of the HDSR Star Party of last October may now like to pool their experiences together and come up with a ‘HDSR Seven Wonders of the Night Sky’ as suggested by Ajay Talwar, perhaps with locations like the wonderfully dark HDSR in mind. If they do, I wonder how many of the objects in my list will also find a place in theirs!