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Erzurum İhsan Doğramacı Foundation Bilkent Laboratory School
Astronomy
/
AstroPhysics
February / March 2013
Astronomy Feb _March 2013_Pack 1 Page 1 of 15
ContentsHow Comets Work.......................................................................................................................................3
Nucleus of Halley’s comet taken from the Giotto mission...................................................................3
Parts of a Comet..........................................................................................................................................3
Comet dust seeding life to Jupiter moons?.................................................................................................5
Comet Ison – due to be visible in November 2013......................................................................................7
Stardust Mission Overview..........................................................................................................................9
A meteor near Chelyabinsk in central Russia.............................................................................................11
Meteoroid Facts........................................................................................................................................13
Understanding the Moon Phases..............................................................................................................14
Phases of the Moon Explained..................................................................................................................15
Astronomy Feb _March 2013_Pack 1 Page 2 of 15
How Comets Work
by Craig Freudenrich, Ph.D.
(from: http://science.howstuffworks.com/dictionary/astronomy-terms/comet3.htm)
Nucleus of Halley’s comet taken from the Giotto
mission.
(This is a false color image of the nucleus of Halley’s comet
taken from the Giotto mission. Note the jets of evaporating gas
coming from the nucleus on the left side.)
Courtesy of NASA/NSSDC Planetary Image Archives
Parts of a Comet
As a comet approaches the sun, it warms up. During this
warming, you can observe several distinct parts:
nucleus
coma
hydrogen envelope
dust tail
ion tail
The nucleus is the main, solid part of the comet. The nucleus is usually 1 to 10 kilometers in
diameter, but can be as big as 100 kilometers. It can be composed of rock.
The coma is a halo of evaporated gas (water vapor, ammonia, carbon dioxide) and dust that
surrounds the nucleus. The coma is made as the comet warms up and is often 1,000 times larger
Astronomy Feb _March 2013_Pack 1 Page 3 of 15
than the nucleus. It can even become as big as Jupiter or Saturn (100,000 kilometers). The coma
and nucleus together form the head of the comet.
Surrounding the coma is an invisible layer of hydrogen called the hydrogen envelope; the
hydrogen may come from water molecules. It usually has an irregular shape because it is
distorted by the solar wind. The hydrogen envelope gets bigger as the comet approaches the sun.
The comet’s dust tail always faces away from the sun. The tail is made of small (one micron)
dust particles that have evaporated from the nucleus and are pushed away from the comet by the
pressure of sunlight. The dust tail is the easiest part of the comet to see because it reflects
sunlight and because it is long, several million kilometers (several degrees of the sky). The dust
tail is often curved because the comet is moving in its orbit at the same speed that the dust is
moving away, much as water curves away from the nozzle of a moving hose.
Comet Halley as it appeared in several images from the 1910 apparition. The comet’s tail
gets bigger as it gets closer to the sun and then decreases as it moves away from the sun.
Astronomy Feb _March 2013_Pack 1 Page 4 of 15
Photo courtesy NASA/JPL
Comets often have a second tail called an ion tail (also called the plasma or gas tail). The ion
tail is made of electrically charged gas molecules (carbon dioxide, nitrogen, water) that are
pushed away from the nucleus by the solar wind. Sometimes, the gas tail disappears and later
reappears when the comet crosses a boundary where direction of the sun’s magnetic field is
reversed.
--- --- --- ---
Comet dust seeding life to Jupiter moons?
by Staff Writers Boulder, Colo. (UPI) Feb 15, 2013
(from:
http://www.spacedaily.com/reports/Comet_dust_seeding_life_to_Jupiter_moons_999.html)
Comet dust may have seeded Jupiter’s moons, including Europa and its liquid ocean beneath an
icy crust, with the raw ingredients for life, U.S. researchers say.
Asteroids and comets rich in the carbon-containing compounds that are key to life on Earth have
been captured by Jupiter’s gravity, becoming orbiting moons that frequently collided as they
settled into new orbits billions of years ago and created a fine dust of those compounds, they say.
The question is, where has all that dust gone?
Computer models suggest Jupiter should have captured about 70 million gigatons of rocky
material but less than half that amount remains as irregular moons orbiting the planet.
William Bottke of the Southwest Research Institute in Boulder, Colo., said the ground-up
material would have fallen toward Jupiter, dragged by gravity and blown by the solar wind and
almost half of it would have hit Jupiter’s largest moons, including Callisto, Ganymede and
Europa.
Astronomy Feb _March 2013_Pack 1 Page 5 of 15
Images from NASA’s Galileo spacecraft have shown dark material on Ganymede and Callisto.
“Callisto literally looks like it’s buried in dark debris,” Bottke told NewScientist.com, noting the
surface of Ganymede looks similar.
In comparison, Europa’s surface appears relatively clean but cracks in the moon’s icy crust
suggest material is being cycled from the surface to deeper inside.
Carbon-rich debris settling on Europa may have been incorporated into the ice and made it into
the ocean, Bottke said.
“Would it be important in Europa’s ocean? It’s hard to say,” he said. “But it is kind of interesting
to think about.”
--- --- --- ---
Astronomy Feb _March 2013_Pack 1 Page 6 of 15
Comet Ison – due to be visible in November 2013
Posted by obelkobusnel on February 25, 2013
COMET ISON: BRIGHTER THAN THE FULL MOON . . . (?)
A comet is a small object that, when it approaches the
sun, develops a visible coma (atmosphere) and
sometimes a tail or two tails – these two traits
distinguish comets from asteroids (comets that approach
the sun and do not present these features are called
extinct comets). Most comets originate from the Kuiper
Belt or the Oort Cloud and have orbital periods ranging
from a few years to many centuries, but some pass
through the inner solar system only once before entering interstellar space. Comet Encke has an
orbital period of three years, the shortest of any known comet, while Comet Catalina‘s orbital
period is estimated to be about six million years – its last sighting was recorded on March 23,
1999.
The brightest comet in recorded history has been Caesar’s Comet. It was observed on May 18,
44 BCE in modern-day Beijing and July 23-25, 44 BCE in Rome. It is only one of five comets in
recorded history to have had a negative magnitude at -4.0. In the spring of 1910, Halley’s Comet
appeared with an apparent magnitude of around 0. Comet Hale-Bopp, also the Great Comet of
1997, became visible with the naked eye in May 1996 and had a magnitude of around 10.6. In
the winter of 2013, Comet Ison will become visible to the naked eye, and some scientists
estimate that it will reach magnitude -11.6 – brighter than the full moon.
Comet Ison (officially C/2012 S1) was discovered on September 21, 2012 by Vitali Nevski from
Vitebsk, Belarus. Its orbital period is not currently known, but it will reach perihelion on
November 28, 2013 at a distance of 1.1 million kilometers from the surface of the sun.
Observation of the comet has led some scientists to believe that Comet Ison and Newton’s
Astronomy Feb _March 2013_Pack 1 Page 7 of 15
Comet, which reached maximum brightness of 2 on December 29, 1680, may have fragmented
from the same parent body.
- RA
Image: An artist’s rendition of the Earth as it passes through the tail of Comet Ison, an event
which is expected to occur during January 2014. This could create a meteor shower around
January 14 or 15, 2014. (Source:
http://frenchtribune.com/sites/default/files/imagecache/article/comet-ison-sky-in-2013.jpg
Sources:
http://www.huffingtonpost.com/2012/12/31/comet-coming-in-2013-ison_n_2388685.html
http://www.independent.co.uk/news/science/brighter-than-a-full-moon-the-biggest-star-of-2013-
could-be-ison–the-comet-of-the-century-8431443.html
http://www.space.com/17918-9-most-brilliant-great-comets.html
--- --- --- ---
Astronomy Feb _March 2013_Pack 1 Page 8 of 15
Stardust Mission Overview
Stardust is the first U.S. space mission which is ….
dedicated solely to the exploration of a comet,
and
the first robotic mission designed to return extraterrestrial material from outside
the orbit of the Moon.
The Stardust spacecraft was launched on February 7, 1999, from Cape Canaveral Air Station,
Florida, aboard a Delta II rocket.
The primary goal of Stardust is to collect dust and carbon-based samples during its closest
encounter with Comet Wild 2 – pronounced “Vilt 2″ after the name of its Swiss discoverer – is
a rendezvous scheduled to take place in January 2004, after nearly four years of space travel.
Additionally, the Stardust
spacecraft will bring back
samples of interstellar dust,
including recently discovered
dust streaming into our Solar
System from the direction of
Sagittarius. These materials
are believed to consist of
ancient pre-solar interstellar grains and nebular that include remnants from the formation of the
Solar System. Analysis of such fascinating celestial specks is expected to yield important
insights into the evolution of the Sun its planets and possibly even the origin of life itself.
In order to meet up with comet Wild 2, the spacecraft will make three loops around the Sun. On
the second loop, its trajectory will intersect the comet. During the meeting, Stardust will perform
Astronomy Feb _March 2013_Pack 1 Page 9 of 15
a variety of tasks including reporting counts of comet particles encountered by the spacecraft
with the Dust Flux Monitor, and real-time analyses of the compositions of these particles and
volatiles taken by the Comet and Interstellar Dust Analyzer (CIDA). Using a substance called
aerogel, Stardust will capture these samples and store them for safe keep on its long journey back
to Earth. This silica-based, material has been inserted within the Aerogel Collector Grid, which
is similar to a large tennis racket. Not until January 2006, will Stardust and its precise cargo
return by parachuting a reentry capsule weighing approximately 125 pounds to the Earth’s
surface.
Stardust is the fourth NASA Discovery mission to be chosen and follows on the heels of Mars
Pathfinder, the Near Earth Asteroid Rendezvous (NEAR) mission, and the Lunar Prospector
mission. The Discovery Program, is an ongoing program that is intended to offer the scientific
community opportunities to accomplish frequent, high quality scientificinvestigations using
innovative and efficient management approaches. It seeks to keep performance high and
expenses low by using new technologies and strict cost caps.
Stardust is managed for NASA’s Space Science Division by the Jet Propulsion Laboratory (JPL),
a division of the California Institute of Technology (Caltech). Stardust is a collaborative
partnership between the University of Washington, Lockheed Martin Astronautics and
JPL/Caltech. The principal investigator, Dr. Donald Brownlee of the University of Washington
leads a global team of scientists worldwide.
--- --- --- ---
Astronomy Feb _March 2013_Pack 1 Page 10 of 15
A meteor near Chelyabinsk in central Russia
A meteor caused quite a stir near Chelyabinsk in
central Russia last week. While countless tiny
meteors fly across Earth’s sky every day, this
particular ‘shooting star’ was much more
spectacular – video footage of the event shows a
fireball streaking across the sky before
exploding.
Most meteors don’t cause much damage but this one exploded with a force many times more
powerful than an atomic bomb. The shock-wave caused by the explosion damaged buildings and
shattered windows. Many people were injured by the blast, mainly from broken glass.
Many meteors start out as asteroids. Asteroids are bodies made of minerals and metals that orbit
the sun, but are too small to be considered planets. They range in size, with the largest being
hundreds of kilometers wide.
NASA estimates that as it hit the atmosphere, the meteor was about 17 meters across and
weighed 10 000 tons. The reason that this event wasn’t predicted was that the asteroid was too
small and dark to be detected – yet it still packed quite a punch!
In relation to the Earth, asteroids can be zipping by at high speeds through the vacuum of space.
When an asteroid’s orbit comes close to that of a planet, such as the Earth, the planet’s stronger
gravitational attraction pulls the asteroid towards it. When it hits the atmosphere, it is called a
meteor.
Friction with the Earth’s air heats the meteor, making it so hot that the rock starts to burn up. If
you look up into the night sky, you might see shooting stars – these are objects burning up as
they enter the Earth’s atmosphere. Most meteors disintegrate into dust and gas. Some break into
pieces that can still strike the ground, where they can be found as meteorites.Astronomy Feb _March 2013_Pack 1
Page 11 of 15
Large meteorites have crashed into the Earth before. The most common theory explaining the
extinction of the dinosaurs points to a huge meteorite that hit the region around Mexico. Such
events have the power to dramatically alter the Earth’s environment on a global scale. So while
the Chelyabinsk meteor might have been small fry in cosmic terms, it is still a reminder of the
potential impact that asteroids might have on our planet.
More information
European Space Agency: Russian asteroid strike
NASA: Russian meteor not linked to asteroid flyby
Meteorite soars over Russia (includes video)
Name that space rock (infographic)
--- --- --- ---
Astronomy Feb _March 2013_Pack 1 Page 12 of 15
Meteoroid Facts
Learn the differences between the terms used to describe them, how fast they travel, how often they make it through Earth’s atmosphere and much more…
A meteoroid is a small rock or particle of debris in our solar system. They range in size
from dust to around 10 metres in diameter (larger objects are usually referred to as
asteroids).
A meteoroid that burns up as it passes through the Earth’s atmosphere is known as a
meteor. If you’ve ever looked up at the sky at night and seen a streak of light or ‘shooting
star’ what you are actually seeing is a meteor.
A meteoroid that survives falling through the Earth’s atmosphere and colliding with the
Earth’s surface is known as a meteorite.
The fastest meteoroids travel through the solar system at a speed of around 42 kilometres
per second (26 miles per second).
The Earth’s atmosphere experiences millions of meteors every day.
Meteors are easier to see during the lower light conditions of night.
A small percentage of meteoroids fly on a path that goes into the Earth’s atmosphere and
then back out again, they are known as Earth grazing fireballs.
When many meteors occur in a close time frame in the same part of the sky it is called a
meteor shower.
Around 500 meteorites reach the Earth’s surface every year but of those only around
5 ever make it to scientists for study.
Meteorites that are observed as they fall through the Earth’s atmosphere and later
recovered are called ‘falls’, all others are called ‘finds’. To this date there have been
around 1000 collected ‘falls’ and 40000 ‘finds’.
--- --- --- ---
Astronomy Feb _March 2013_Pack 1 Page 13 of 15
Understanding the Moon PhasesHave you ever wondered what causes the moon phases? We all know that its appearance
changes over time. But why?
The good way to understand the phases of the moon is to examine an earth-moon-sun
diagram:
Astronomy Feb _March 2013_Pack 1 Page 14 of 15
Phases of the Moon Explained
The illustration may look a little complex at first, but it's easy to explain.
Sunlight is shown coming in from the right. The earth, of course, is at the center of the diagram.
The moon is shown at 8 key stages during its revolution around the earth. The moon phase name
is shown alongside the image.
The dotted line from the earth to the moon represents your line of sight when looking at the
moon. To help you visualize how the moon would appear at that point in the cycle, you can look
at the larger moon image.
This means for the waning gibbous, third quarter, and waning crescent phases you have to
mentally turn yourself upside down. When you do this, you'll "see" that the illuminated portion is
on your left, just as you see in the large image.
One important thing to notice is that exactly one half of the moon is always illuminated by the
sun. Of course that is perfectly logical, but you need to visualize it in order to understand the
phases. At certain times we see both the sunlit portion and the shadowed portion -- and that
creates the various moon phase shapes we are all familiar with. Also note that the shadowed part
of the moon is invisible to the naked eye; in the diagram above, it is only shown for clarification
purposes.
So the basic explanation is that the lunar phases are created by changing angles (relative
positions) of the earth, the moon and the sun, as the moon orbits the earth.
http://www.moonconnection.com/moon_phases.phtml
Astronomy Feb _March 2013_Pack 1 Page 15 of 15