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Transcript
Newsletter
Volume 2, Issue 7
July 2013
PAKISTAN SPACE & UPPER ATMOSPHERE
RESEARCH COMMISSION
2013
contents
B U L L E T I N
Volume-2, Issue 7, July 2013
Pakistan’s Space Vision 2040, was approved
by the Prime Minister of Pakistan which interalia included augmentation / strengthening
of the Astronomy and Astrophysics program
of SUPARCO. SUPARCO`s astronomy and
astrophysics program is mainly focused on
theoretical and observational research, for which
an astronomical observatory is planned to be
established. Research studies pertaining to deep
space objects including galaxies, nebulae and
variable stars are also being initiated. Search for
earth-like planets is a hot topic in astrophysics
nowadays. It is planned to conduct research
studies in this field also.
1)Uranus
Pg : 01
2)
Quasi Stellar Radio Source (QUASAR)
Pg : 04
3)
Book Review
Pg : 07
4)
Events of this month
Pg : 09
5)
Monthly science news
Pg : 15
6)
Monthly Star Guide
Pg : 17
7)
Understanding Space Weather (Part 13) GNSS & Space Weather
Pg : 21
8)
Universe Today
Pg : 24
URANUS
A cold gas giant, Uranus is the third
larger planet in the solar system. Its
most unusual characteristic is that its
axis of rotation lies almost in the plane
of its orbit, and so it seems to orbit
the Sun on its side. Although it can be
seen with the naked eye when at its
brightest, Uranus was not discovered
until 1781, when it was found by a
British astronomer, William Herschel.
01
Uranus’s aurorae against its equatorial rings,
imaged by the Hubble telescope
ATMOSPHERE
AND CLIMATE
Uranus is covered in the methane clouds
that absorb red light, giving the planet
greenish appearance. Its disk is nearly
featureless, but some bright clouds were
seen by the Voyager 2 Space probe in 1986
and later by Hubble Space Telescope (HST).
The Planet’s extreme axial tilt means that
in the course of each orbit the Sun appears
overhead at the equator and both Poles;
each pole experience s 42 years of daylight
followed by 42 years of the darkness. The
interior is probably significantly different
from those of Jupiter and Saturn, consisting
mostly of water, methane, ammonia, and
rock, rather than liquid hydrogen.
RINGS AND MOONS
Uranus has 11 thin rings and 21 known moons (six only recently identified and whose orbits
are not yet accurately known). The rings are too faint to be seen with the size of Telescope
used by amateur observers. The outermost ring, called Epsilon ring, is 60miles (100 km) wide
and has “shepherd” moons, Cordelia and Ophelia, one on each side. The moons, too, are faint;
even the biggest and brightest, Titania, is of only 14th magnitude and hence cannot be seen
without a large telescope.
OBSERVATION
Under good conditions, and when
its position is known, Uranus can be
located with the naked eye, resembling
a star of 6th magnitude. It is easy to
find with binoculars, even from urban
areas. Its identity can be confirmed
by watching its movements from
night to night. At oppositions, which
occur a year and four days apart, a
magnification of 500times will show
Uranus about the same size as the full
moon.
References:
(1)Stars and Planets by Ian Ridpath
(2) The data book of Astronomy by
Patrick Moore
QUASI STELLAR
RADIO SOURCE
(QUASAR)
Quasi stellar radio sources (Quasars) are the very luminous and most distant objects in the known
Universe. In the early 1960’s quasars were referred to as radio stars because they were discovered to
be a strong source of radio waves. In fact, the term quasar comes from the words, “Quasi-stellar radio
source”. Today, many astronomers refer to these objects as quasi stellar objects. As the resolution
of our radio and optical telescopes became better, it was noticed that these were not true stars
but some type of as yet unknown star-like objects. It also appeared that the radio emissions were
coming from a pair of lobes surrounding these faint star-like objects. It was also discovered that these
objects were located well outside our own galaxy. Quasars are very mysterious objects. Astronomers
today are still not sure exactly what these objects are. What we do know about them is that they
emit enormous amounts of energy. They can burn with the energy of a trillion suns. Some quasars
are believed to be producing 10 to 100 times more energy than our entire galaxy. All of this energy
seems to be produced in an area not much than our solar system.
04
QUASARS MYSTERY
We do know that quasars are extremely distant. In fact, they may be the most distant objects in
the universe. They show largest red-shift of any other objects in the cosmos. Astronomers are able
to measure speed and distance of far away objects by measuring the spectrum of their light. If the
colors of this spectrum are shifted toward the red, this means that the object is moving away from us.
The greater the red shift, the farther the object and the faster it is moving. Since quasars have such
a high red shift, they are extremely far away and are moving away from us at extremely high speeds.
It is believed that some quasars may be moving away from us at 240,000 kilometers per second or
nearly 80% the speed of light. Quasars are, in fact, the most distant objects to ever be detected in the
universe. We know that light travels a certain distance in a year.
Most quasars cannot be seen with small telescopes, but 3C 273, with an average apparent
magnitude of 12.9, is an exception. At a distance of 2.44 billion light-years, it is one of the most
distant objects directly observable with amateur equipment. Quasars are so far away that the light
we see when we observe them has been traveling for billions of years to reach us. This means
that quasars are among the most ancient objects known in the universe. The most distant quasars
observed so far are over 10 billion light-years away. This means we are seeing them as they appeared
10 billion years ago. It is entirely possible that some or all of the quasars we see today may not even
exist anymore.
A VLBA RADIO IMAGE of the quasar
3C 273's core and jet
We still do not know exactly what a quasar is. But the
most educated guess points to the possibility that quasars
are produced by super massive black holes consuming
matter in an acceleration disk. As the matter spins faster
and faster, it heats up. The friction between all of the
particles would give off enormous amounts of light other
forms of radiation such as x-rays. The black hole would
be devouring the equivalent mass of one Sun per year.
As this matter is crushed out of existence by the black
hole, enormous amounts of energy would be ejected
along the black hole’s north and south poles. Astronomers
refer to these formations as cosmic jets. Another possible
explanation for quasars is that they are very young
galaxies. Since we know very little about the evolutionary
process of galaxies, it is possible that quasars, as old as
they are, represent a very early stage in the formation
of galaxies. The energy we see may be ejected from the
cores of these very young and very active galaxies. Some
scientists even believe that quasars are distant points in
space where new matter may be entering our universe.
This would make them the opposite of black holes. But this
is only conjecture. It may be some time before we really
understand these strange objects.
BOOK REVIEW
Major leaps in space technology now allow us to view the splendor and
diversity of the Solar System in remarkable detail. This textbook presents a
fascinating description of the bodies in the Solar System and their origin
and evolution. It highlights important concepts and techniques in boxed
summaries. There are questions and answers throughout the text, as well
as exercises with full solutions. Written and edited by practicing planetary
scientists, this new edition has been updated to reflect current knowledge and
contains new figures to bring it up to date. It is ideal for introductory courses
on the subject and is suitable for self-study. Online resources include electronic
versions of figures from the book, sample assignments with suggested answers
and links to websites featuring video clips and news stories related to the
textbook.
Compiled by a team of experts, this textbook has been designed for
elementary university courses in planetary science. It starts with a tour of
the Solar System and an overview of its formation that reviews in detail
the terrestrial planets, giant planets and minor bodies. It concludes with a
discussion of the origin of the Solar System. The text contains numerous
useful learning features such as boxed summaries, student exercises with full
solutions, and a glossary of terms. It is also supported by a website hosting
further teaching materials.
07
EVENT OF
THIS MONTH
July 8 - New Moon. The Moon will be directly between the Earth
and the Sun and will not be visible from Earth. This phase occurs
at 07:14 UTC.
09
July 22 - Full Moon. The Moon will be
directly opposite the Earth from the Sun
and will be fully illuminated as seen from
Earth. This phase occurs at 18:15 UTC.
11
July 28, 29 - Southern Delta
Aquarids Meteor Shower. The
Delta Aquarids can produce
about 20 meteors per hour
at their peak. The shower
usually peaks on July 28 &
29, but some meteors can
also be seen from July 18 August 18. The radiant point
for this shower will be in the
constellation Aquarius. The last
quarter moon will be around
for the show and may hide
some of the fainter meteors.
Best viewing is usually to the
east after midnight.
13
MONTHLY
SCIENCE NEWS
15
A Hubble View of NGC 1579: The Trifid of
the North
Unlike the venomous fictional plants that
share its name, the Trifid of the North,
otherwise known as the Northern Trifid or
NGC 1579, poses no threat to your vision.
The nebula’s moniker is inspired by the
better-known Messier 20, the Trifid Nebula,
which lies very much further south in the
sky and displays strikingly similar swirling
clouds of gas and dust.
Black Holes Abundant Among the
Earliest Stars
By comparing infrared and X-ray
background signals across the same
stretch of sky, an international team of
astronomers has discovered evidence
of a significant number of black holes
that accompanied the first stars in the
universe
First Evidence of
a New Phase in
Neutron Stars
The nuclear ‘pasta’,
called as such due its
similarity to the Italian
food, limits the period
of rotation of pulsars,
and the University of
Alicante has detected
the first evidence of
existence of a new
phase of matter in the
inner crust of neutron
stars
New Kind of Variable Star Discovered:
Minute Variations in Brightness Reveal
Whole New Class of Stars
The Swiss are justly famed for their
craftsmanship when creating extremely
precise pieces of technology. Now a
Swiss team from the Geneva Observatory
has achieved extraordinary precision
using a comparatively small 1.2-metre
telescope for an observing programme
stretching over many years. They have
discovered a new class of variable stars
by measuring minute variations in stellar
brightness.
Scientists Size Up Universe’s Most
Lightweight Dwarf Galaxy
The least massive galaxy in the known
universe has been measured by UC Irvine
scientists, clocking in at just 1,000 or so
stars with a bit of dark matter holding
them together.
NASA’s Chandra Turns Up Black Hole Bonanza in
Galaxy Next Door
Using data from NASA’s Chandra X-ray Observatory,
astronomers have discovered an unprecedented
bonanza of black holes in the Andromeda Galaxy, one of
the nearest galaxies to the Milky Way.
Shining a Light On Cool Pools
of Gas in the Galaxy
Newly formed stars shine brightly,
practically crying out, “Hey, look
at me!” But not everything in our
Milky Way galaxy is easy to see.
The bulk of material between
the stars in the galaxy -- the cool
hydrogen gas from which stars
spring -- is nearly impossible to
find.
16
MONTHLY STAR
GUIDE
This is the best time for
northern observers to see the
rich southern constellations
Sagittarius and Scorpius. The
center of our Galaxy is in
Sagittarius, so the Milk Way star
fields are particularly dense
in this region. For southern
observers, these constellations
are almost overhead and
dominate the scene.
Northern Latitudes
Looking North
Ursa Minor (the Little Bear) remains well placed, with Darco coiled around it. The Big dipper
(Plough) is in the northwest, with Cassiopeia and Cepheus in the northeast, The great Square
of Pegasus is rising in the east, while Arcturus, in Bootes, remains high in the west.
17
Looking South
Due south, Ophiuchus is entwined by both halves of Serpens with Hercules above it. In
the east, the Summer Triangle of Vega, Deneb, and Altair is well placed. Antares in Scorpius
is near the southern horizon, with Sagittarius visible to its left for observers in southerly
locations. Virgo is setting in the far west.
19
Reference: Stars and Planets
By Ian Ridpath
UNDERSTANDING
SPACE WEATHER
(PART 13)
GNSS & SPACE
WEATHER
Satellite based navigation (or in short
SatNav) has gained tremendous
momentum particularly over the past
decade and has found use in a large
variety of domains spanning from
civil to military applications. Global
Positioning System (GPS) has long
been offering positioning accuracies
down to meter level. With the further
addition of recently introduced Global
Navigation Satellite Systems (GNSS),
the SatNav is becoming capable of
offering increasingly wider temporal
and spatial coverage in addition to
higher accuracies, which makes them
critically essential for modern day
applications.
A typical SatNav system (either GPS or
any other GNSS e.g. Galileo, BeiDou,
GLONASS etc.), relies on wireless
ranging signals transmitted from
satellites in space which are processed
by GNSS receivers to estimate user
position. The best part about GNSS is
its Zero subscription fee to the end
user. The range of GNSS applications
is expanding exponentially and
includes surveying, cartography,
telecommunications, civil aviation,
fleet management, mining, railway
management, maritime navigation,
precision agriculture and land
management. Currently, the users’
accuracy expectations range from
meter level (for e.g. Civil Aviation, Vehicle Navigation,
Location Based Services (LBS), Marketing) down to millimeter
level (for e.g., surveying, geology applications). Reliance on
GPS/GNSS has increased to the extent that it’s being referred
to as the 4th utility after water, electricity and natural gas.
However, like any other system relying on wireless links,
GNSS is vulnerable.
The GNSS signals pass through space before reaching the
user terminal. Consequently, the space weather’s effect
on these signals become of critical concern. The space
weather, as has been discussed in previous issues of A&A
newsletters, results due to variations in solar activities.
These activities occur in recurring cycles with maxima and
minima marking the two extremes. These variations result
in irregular ionosphere densities causing signal attenuation,
absorption and reflection. In addition, it also results in
change in the direction of signal propagation as well as that
of its amplitude and phase. At user’s end, these effects result
in position accuracy degradation, worsening signal qualities
and even loss of signals altogether.
21
A number of events have been recorded over
the years causing GPS service disruptions.
Several hours of GPS accuracy degradation
was experienced during July 14-17, 2000 in
USA alone. Due to Coronal Mass Ejection
(CME) event over October 29-31, 2003, the
GPS based positioning system for aviation
(Wide Area Augmentation System – WAAS)
was severely impacted for 11-15 hour periods.
Furthermore, affected GPS based survey
instruments were reported from around the
globe. On January 20, 2005, 26 flights were
forced to operate on sub-optimal polar routes
due to affected GPS based navigation caused
by solar flare occurrence. On December 6, 2006,
an extremely large solar radio burst affected
GPS receivers over the entire sunlit side of the
Earth (Ref: Meehan, Murtagh, “Space Weather &
GPS Reliant Industries”, 2010). On March 7, 2012,
the sun unleashed an X5.4-class solar flare, the
largest in 6 years – this could possibly be the
warning shot at the beginning of the new solar
maximum?
The dense and thick ionosphere arising during
the next solar maximum can affect GPS signals,
at all latitudes. At high latitudes, the northern
lights (aurora) can disrupt GPS signals. At tropical
latitudes, the ionosphere can create its own
storms resulting in denser, thicker ionosphere.
At mid-latitudes, the ionosphere can experience
storms driven by solar flares and magnetic
storms. Potentially affected operations/users
may include aviation services, search and rescue
operations, public safety and security services,
communication networks, electricity distribution
networks, financial services, military operations
and etc.
Considering that the happenings are real and
have higher possibilities of occurring again, one
must take proactive measures while relying on a
navigation system so heavily. Threat assessment
is the first and a major step for developing
system resilience. Remedial action may include
the following:
•
Design scintillation-resistant GPS receivers
•
Use of dual frequency receivers offering
higher robustness to ionospheric scintillation,
•
Improvement of space weather prediction
through extensive observation and modeling,
•
Use of multi-GNSS receivers to avoid
reliance on any individual system and most
importantly
•
Identification and implementation of back
up techniques
Conclusively, while it is impossible to understate
the importance of GNSS in modern era, it must
be used with caution and awareness about its
vulnerabilities particularly to space weather.
Remedial actions are important and can help
avoid potential socio-economic mishaps.
UNIVERSE TODAY
24
www.universetoday.com
Universe Today (UT) is a non-commercial space and astronomy news site, founded in 1999 by Fraser
Cain and edited by Nancy Atkinson. The news can then be discussed on the forums. The forum
began on 24 July 2003, and was mainly used to discuss the Universe Today news as well as ask spacerelated questions and discuss alternate theories. In early September 2005, the forum merged with
that of Bad Astronomy combined to form the BAUT forum. The website's viewership attains several
million people per year.
Emily Lakdawalla, of The Planetary Society, said that she relies on Universe Today and Bad Astronomy
to "give ... an independent look at big news stories" and that UT plays a key role in space-related
journalism, along with other websites such as Space.com. Several peer-reviewed papers have
mentioned Universe Today as being a space-related news website.
In 2008 the site was briefly banned for about a day from Digg.com, and then unbanned. In March
2011, Businessweek reported that the site had lost 20 percent of its traffic in five days after a change
in the page ranking algorithm of Google. In April 2011, the Association of British Science Writers
noted that Universe Today decided to ignore embargoed stories.
PA K I S TA N S PA C E & U P P E R AT M O S P H E R E
RESEARCH COMMISSION
Contact Information
SPAS Directorate
Gulzar-e-Hijri SUPARCO Road
Sector 28, SUPARCO, Karachi, Pakistan
Tel: 021-34690765-74
Fax 021-34690795
Email: [email protected]
SUPARCO - ASTRONOMY &
ASTROPHYSICS Bulletin is a
monthly publication
Designed by: Aley Ali Naqvi