Erzurum İhsan Doğramacı Foundation Bilkent Laboratory School

Astronomy

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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

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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

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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.

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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.

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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.

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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.”

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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

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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

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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

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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.

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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

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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)

 

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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’.

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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:

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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

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