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.”
[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.
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.
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!
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