CYGNUS X-1
The Astronomy Club Wall Magazine
Cygnus X-1, the astronomy club wall
magazine first issue of this term is here. The wall mag contains articles of
general interest. It will have the list of upcoming events, astronomy news,
cool astro stuff and some general articles on and about astronomy.
The
name of the magazine is derived from first ever discovered black hole in
constellation Cygnus, the ‘X’ denoting an object of unknown type, and ‘1’ is
the first object in the series of these ‘unknown objects’.
Comments and suggestion for improving this wall magazine are cordially invited.
Feel free to ask questions
about general astronomy and do give us your feedback.
The membership is free for everyone. All you have to do is to come to observation sessions regularly. In our tenure you can't join whenever you wish you were supposed to register before 25th of Aug 2000 to be a club member. If you want to become a member of club give your names and login to any of the coordinators before 25-Aug.
175-II
257-II 257-II
virmani@iitk.ac.in kmittal@iitk.ac.in
hkhatri@iitk.ac.in
· Observation Sessions
Observation sessions are organized by the club to introduce new members
to the basic of sky gazing. Beginners are taught to handle telescope, read star
charts, and the more advanced members go for deep sky objects- Galaxies, Star
clusters, Nebulae etc.
· Slide show and Lectures
Club
also organizes slide shows in the semester to give a feel of the subject.
Lectures on the various motions in the sky and general astronomy are held, too.
· Long Projects
Currently we are working on 137 MHz radio telescopes for exploring our solar system at radio wavelength. For those who wish to make a telescope on their own we have telescope making tutorials and instruments. We have also decided to build an observatory for installing our 8” telescope (designed and fabricated by our club).
· Astrophotography
We also take photograph of constellations, planets, moon and other deep sky objects. This activity will start as soon as the sky clears out. There will be notices put up accordingly in this regard.
· Web Site
The club has a website of
its own which is upgraded regularly. Go to the URL: http:/www.iitk.ac.in/ac/index.htm
What’s up in the Sky?
August is the most popular
time of year to observe. The backdrop to this action is the spectacular summer
Milky Way, arching from our galaxy's central bulge at the southern horizon
through the dark Great Rift lying overhead.
The brightest stars of summer, Deneb overhead, Vega to its west, and Altair below to the south, form the Summer Triangle. They frame the Milky Way at the zenith as it arches across a dark sky.
The brilliant Vega shines nearly straight overhead at his time of the year after dark, the Great Square of Pegasus looms low in the east, balanced on one corner.
Stay up late to observe the
gas giant planets Jupiter and Saturn. Rising near midnight, the pair swapped
places since we last saw them in spring. On August 21, the moon forms a nice
line with Saturn and Jupiter. The moon then slides below Saturn on the next
night and below Jupiter on the 23rd. Saturn's rings have tilted 24° toward us,
almost as much as they can, providing an exceptional 3-D view.
Uranus and Neptune are in the southeast during evening. Pluto (magnitude 14 in Ophiuchus) is high in the south-southwest right after dark.
Constellation of the Month
Abbreviation : Cyg
English
name : Swan (or The Northern Cross)
General:
It is the conspicuous constellation of the northern
hemisphere. It belongs to the Hercules constellation family. The stars forming
the swan’s body resemble a cross, so sometimes this constellation is referred
as Northern Cross. The brightest star (spectral type A2Iae;
1.25 mag), alpha Cyg, called Deneb (Arab: the tail), is
among the 20 brightest stars in the sky.
The northern border of this constellation reaches as high as DECL=+60 degrees;
to the south it extends down to about DECL=+28 degrees. From east to west it
lies between RA=22h to RA=19h 10m (average).
Mythological
Background:
Cygnus, the swan, is one of the two birds
(Aquila, the eagle, is the second), which are hunted by Hercules. Yet it seems
that the two birds were lucky and have escaped. It is assumed that these birds
(together with a third one, the Vulture - nowadays the constellation Lyra)
represent the Stymphalian Birds - one of the tasks of Hercules. (See: Peterson
Field Guide to the Stars).
Particulars:
Color
in Astronomy
In Astronomy, colors are not defined as
such. The astronomers talk in terms of wavelength. To them a color simply
reflects the relative intensity of its range of radiations in visible spectrum
as compared to the others. Unfortunately, the wavelength ranges often used by
the astronomers do not correspond to those perceived by human eyes. Our eyes
are more sensitive to red and green colors. But astronomers use filters having
mutually exclusive and exhaustive ranges of wavelengths. These are essentially
‘u, g, r, i’ filters corresponding to ‘ultraviolet, green, red, infrared’
respectively. Please note that these filters cover the entire range and are
still non-overlapping. In fact two important requirements of good filter set
are –
i)
Minimum
overlapping
ii)
Maximum
Range
Here we discuss few of the important color
measurements that filters allow.
Stars:
Early in this century, little was known
about stars, and particularly, no one knew why some stars looked red, white,
yellow, or blue for the instant. One of the earliest applications of color was
simply looking at the blue light versus the green light from stars. In fact, in
those days many scientists guessed that the color was an evolutionary sequence
revealing the fact that the bluest stars were the youngest and they slowly grew
cooler and older, resulting in red stars. One of the first systematic attempts
to measure the color of stars was carried out independently by Hertzsprung
(1911) and Russell (1913). In doing so, they very quickly discovered that
nearly all stars inhabit common characteristics. Astronomers evaluating their
results (HR diagram) soon came to know
that the stars didn't evolve from the blue end to the red end of the main
sequence. Rather, the colors were a sequence in stellar mass, with more massive
stars being brighter and bluer and the smaller stars redder and fainter.
Color
Red shifts:
Now lets move from the historic to the
state-of-the-art. In the 1990's, one of the most exciting fields of astronomy
was early galaxy evolution. Because light from distant galaxies experiences a
red shift, one can estimate the distance of a galaxy by measuring the amount of
shift. But, because the light had to travel all that way, we're also seeing
very old light, emitted when that galaxy was very young. In this way, we can
see galaxies, as they were very early in the universe simply by looking more
deeply into the heavens. However, the light from these galaxies is incredibly
faint. Estimating red shifts from individual spectral features from such a
faint source is extremely difficult, so the classification based on spectrum is
critical. These type of attempts have added lot to the understanding of the
universe.
Beyond the Optical:
Color and filter methods are workhorses
not only in the optical field but also in other wavelength regimes, such as the
radio, infrared, ultraviolet and X-ray. Currently, the Chandra X-ray
Observatory is gathering the first truly high-resolution images of countless
objects in the universe and using wavelength information to determine
temperatures on the order of millions of degrees in places like supernova
remnants, clusters of galaxies and black hole
environments. Ultraviolet colors tell us about the hot atmospheres
of stars; and infrared colors tell us about how stars are forming.
We have just talked about the application
of color measurements in regimes as diverse as the edge of the universe, the
atmospheres of planets and the environs of black holes, yet this smattering of
examples does little justice to the utility of color in astronomy. Virtually
every astrophysical problem has been addressed with color, and a large fraction
of journal articles in the field make at least some reference to color.
Meanwhile, plans to enhance the space telescope with new instruments will take
advantage of color information to help unravel the mysteries of star and planet
formation. Very large telescopes will continue to push deeper and deeper in
search of the first galaxies, with color as their guide. Color has been one of
the most fruitful measurements in astronomy's past and will certainly continue
to be in the near future!!!