Astronomy-Brhamand

7/24/2019 Astronomy-Brhamand

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About DAY & NIGHT

Why Does Earth have day and Night?

While you don't feel it, Earth is spinning. Once every 24 hours Earth turns or rotates on its axis taking all of us with it. When we are on the side ofEarth that is facing the Sun, we have daylight. As Earth continues its spin, weare moved to the side facing away from our Sun, and we have nighttime. Ifwe were looking down on Earth from above the north pole, we could see thatEarth rotates counterclockwise, and we would watch daylight and darknesssweeping across our globe from east to west.

Do other planets have day and Night?

Yes! All the planets in our solar system spin on their axes (so does our Sun!)and so they have day and night cycles. There are differences, however, in thelength of day and nightthe cycles are made even more complex by the tiltof a planet's axis and its rate of orbit. Some planets rotate faster than Earthand some rotate slower. Mars has a day and night cycle similar to Earth. Marsrotates on its axis once every 24.6 hours. Venus turns once on its axis every243 Earth days (which is only slightly longer than it takes for Venus to goaround the Sun!). Mercury's day and night cycle is more complex. Mercuryrotates one-and-a-half times during each orbit around the Sun. Because ofthis, Mercury's dayfrom sunrise to sunsetis 176 Earth days long. Thelarger planets spin much faster. Jupiter rotates once every 10 hours, Saturnspins once every 11 hours, and Neptune completes a rotation in 16 hours.

Pluto, at the farthest reaches of our solar system, spins on its axis once every6.4 days.

Something to ponder: Does Pluto even have a day and night like we

think of on Earth? Pluto is so distant from the center of our solar system thatour Sun would look like a very bright star in its sky!


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Why does earth day length changes over the year?

Every location on Earth experiences an average of 12 hours of light per daybut the actual number of hours of daylight on any particular day of the yearvaries from place to place. Locations around Earth's equator only receiveabout 12 hours of light each day. In contrast, the north pole receives 24 hoursof daylight for a few months in the summer and total darkness for months inthe winter. These two annual times of light and dark are separated by a longsunrise and a long sunset.

Earth rotates on its axis; this causes us to experience day and night. ButEarth's axis is tilted 23.5 degrees (the angle is measured between Earth'sequatorial plane and the plane in which it orbits our Sun). As Earth orbits ourSun, the axis points toward the same location in space almost directlytoward Polaris, the North Star. This means that during Earth's movementaround our Sun each year, our polar regions spend loooooooong periods

pointed toward our Sun in the summer (for example, July in the northernhemisphere, or December in the southern hemisphere) and long periods

pointed away from our Sun during the winter. At latitudes greater than66.5 degrees (90 degrees minus 23.5 degrees, the tilt of the axis), the regions

above the Arctic and Antarctic circles on our globe, days of constant darknessor light occur.


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Because of this tilt and Earth's movement around our Sun, there is a timewhen Earth's north pole is tilting 23.5 degrees toward our Sun. This is thesummer solstice, the first day of the northern hemisphere summer and thelongest day of the year in the northern hemisphere. On December 21 or 22,

Earth's north pole is tilting 23.5 degrees away from our Sun and the southpole is tilted toward our Sun. This is the winter solstice, the shortest day ofthe year in the northern hemisphere. Twice each yearduring the equinoxes(equal nights) Earth's axis is not pointed toward our Sun. The springequinox in March marks the beginning of the transition from 24 hours ofdarkness to 24 hours of daylight at the north pole. The fall equinox inSeptember marks the shift into 24 hours of darkness at the north pole. Duringthe equinoxes every location on Earth (excluding the extreme poles)experiences a 12-hour day length.

Other planets also experience these changes in day and night length becausethey too are tilted on their axes. Each planet's axis is tilted at a differentangle. Jupiter is tilted only 3 degrees, so its change in day and night length asit moves around the Sun is less extreme than that of Earth. Neptune's axis istilted 30 degrees, so day and night changes would be more extreme on

Neptune than on Earth. Uranus presents an interesting case because its axialtilt is even more extreme 98 degrees! This means that the north pole ofUranus is pointed at the Sun during the north polar summer; the south pole is

in total darkness. During the north polar winter, some 42 Earth years later,the south polar axis points at the Sun and the north polar region is in totaldarkness. During the spring and fall, when its axis is perpendicular to theincoming rays of the Sun, Uranus experiences a 17-hour day and night cycleas it spins on its axis.

Meteoroids, Meteors, Meteorites . . . Whats the Difference?

Meteoroids are small particlesoften no bigger than a grain of sand thatorbit our Sun. When meteoroids enter Earths atmosphere, they produce

brilliant streaks of light that can be seen in our sky. These brief streaks oflight and the particles that are moving through our atmosphere are


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meteors. Meteorites are rocks from space that actually have landedon Earthsor another planets surface.

How Are Asteroids and Comets Related to Meteorites?

Asteroids are rocky bodies, less than 1000 kilometers across, that orbit ourSun. Asteroids occur in the asteroid belt between Mars and Jupiter. Cometsare masses of ice and dust, less than 10 kilometers across, that usually stay inthe cold outer reaches of our solar system. Meteoroids are small pieces ofasteroids or comets.

Where Do Meteorites Come From?

Most meteorites appear to come from asteroids. This is based on acomparison of the composition of meteorites with our understanding of thecomposition of asteroids, based on remote sensing. It also is based on acomparison of the orbits of asteroids and the orbits of meteoroids, calculatedfrom photographs of the meteoroids as they approached Earth. A fewmeteorites are from the Moon and Mars. These are pieces of the planets thatwere broken off and knocked into orbit when asteroids struck the planets.Meteorites from the Moon are similar to the samples collected by the Apolloastronauts. The Mars meteorites include sealed pockets of gas that scientistsdiscovered contain the same gases as occur in the atmosphere of Mars.

Comets as Meteoroid Sources

Rarely, meteorites may also come from comets. Comets have been calleddirty snowballs because theirnucleustheir solid coreconsists mostlyof ice with a bit of dust, rock particles, and a little organic material mixed in.Most comets are found at the outer edge of the solar system beyond theorbit of Plutoin a region called the Kuiper belt. Some comets reside evenfarther away in a large spherical cloud around our solar system called theOort cloud. Comets are so far away from the Sun that they remain frozen;they are important relics from the earliest times of our solar system. Somecomets do orbit our Sun in periodic, elliptical paths. Comets are nearlyinvisible except when they get close to the Sun. Heat from the Sun vaporizesthe ice on the comet's surface causing gas and dust to flow away and form thecloud of the coma. The solar wind the flow of particles out from the Sun


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sweeps the coma away into a long tail. The tail always points away fromthe Sun because of the solar wind, no matter what direction the comet ismoving in its orbit. The tail actually has twin pieces, agas tailand a dust tail,that can extend for millions of kilometers from the comet nucleus as it travels

around the Sun. As the comet gets very close to the Sun, small pieces of dust,rock grains, and ice are left behind as a trail of meteoroids.

Why Do We Have Meteor Showers?

Meteor showers occur when Earth passes through the trail of dust and gas leftby a comet. The particles enter Earths atmosphere and most burn up in alively light show a meteor shower. Some meteor showers, like thePerseids and the Leonids, occur annually when Earths orbit takes our planet

through the debris path left along the comets orbit.What are Meteorites Made Of?

Scientists classify meteorites into three groups: stony meteorites, ironmeteorites, and stony iron meteorites.

Stony meteoritesmake up about 95% of the meteorites reaching Earth.Stony meteorites include chondritesand achondrites. Chondrites containsmall spheres of silicate minerals called chondrules. There alsoare carbonaceous chondrites stony meteorites that contain water andorganic (carbon) molecules such as simple amino acids.Achondritesare alsostony meteorites, but they do not have chondrules and they have undergoneheating and change. Achondrites include meteorites from our Moon andMars.

Iron meteoritesmake up about 5% of the meteorites found on Earth. Thesehave high amounts of iron and nickel. Iron meteorites are very heavy!

Stony-ironmeteoritesare in between the other two types of meteorites.These are rare only about 1% of the meteorite finds on Earth are stonyiron meteorites.


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What Do Meteorites Tell Us?

Meteorites provide us with information about the processes and materials in

our early solar system. The early solar system did not consist of a sun andplanets. It was a spinning cloud of dust and hydrogen gas that was hotter inthe center and cooler toward the edges. As the gas and dust began to cometogether, chondrules tiny spheres of minerals containing silica condensed. These tiny spheres and dust gradually grew as other particlescollided with them and became attached a process called accretion. Someof the particles grew to the point that they were large enough togravitationally attract other particles, and they accreted all the material intheir path as they orbited the young Sunsome of these became our planets.

Other particles remained small, space rocks left behind after the planetsformed. Accretion is a hot process; when a particle slams into anotherparticle, its motion is converted to heat. The planets and some of the spacerocks became so hot that they began to change, in some cases melting.Melting allowed the bodies to differentiate, with the heavier metals of ironand nickel sinking into a central core, and the lighter materials making amantle and outer crust.

Chondritesare meteorites that contain chondrules. Most chondrites were

heated and changed early in their formation. However, some chondrites havenot changed since they formed. These chondrites provide scientists withessentially unaltered samples of our early solar system. They also help usdetermine the age of our solar system; chondrites are between 4.5 and 4.56

billion years old.

Carbonaceous chondrites are also very old samples of our solar system.They contain water in some of their minerals and organiccompounds. Carbonaceous chondrites provide scientists with more complete

samples of the chemical composition of our early solar system.Achondrites, iron meteorites, andstony iron meteoriteshave differentcompositions. These come from bodies planets and asteroids in oursolar system that were heated and altered, and in some cases melted. The ironmeteoritescome from the metallic cores of asteroids. Achondritesmay befrom the crust. Stony meteoritesare from the mantle, between the iron core


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and the crust. All of these meteorites provide information about thecomposition of the bodies in our solar system, and about the processes thathave shaped it. The differentiated meteorites often have ages of about 4.4

to 4.5 billion years, which tells scientists that differentiation of the asteroids

took place early in the history of our solar system.Some of the achondrites come from the Moon and Mars and some of theseare much younger. These are basalts dark fine-grained volcanic rocks and they help us understand that there were volcanos erupting on these

bodies, as well as give us a timeframe for the eruptions. We know, forexample, that in the last 180 million years, volcanos were erupting on Mars.

What Happens to a Meteoroid On Its Way to Earth?

Not much when it is in space. When the meteoroid enters Earths atmosphere,

things begin to heat up! Actually, it is the air in front of the meteoroid thatheats up. The particle is traveling at speeds between 20 and 30 kilometers persecond. It compresses the air in front, causing the air to get hot. The air is sohot it begins to glowcreating a meteor - the streak of light observed fromEarth. The intense heat also melts the outside of the meteoroid. The tripthrough Earths atmosphere is fast enough that the inside of a meteoroid often

is not heated at all. However, for most rocks from space, even the short trip issufficient to melt away much of it; a meter-sized meteoroid can be reduced tothe size of a baseball. Small meteoroids are vaporized completely. Theatmosphere becomes thicker as the meteoroid gets closer to Earths surface,

causing the rock to slow and cool. The outer melted part of the meteoroidsolidifies, leaving a fusion crust a thin dark glassy rind. Some meteoroids

break up just before they reach Earths surface, creating a fireball

accompanied by an explosion that can be heard kilometers away.

The impact from a large meteoroid striking the surface may leave a crater a circular depression. Large meteoroids leave craters about 10 times theirsize, although the size depends on how fast the meteoroid is moving, its angleof approach, and other factors. Meteor Crater was formed about 50,000 yearsago when the 30-meter-wide Canyon Diablo meteorite struck the ground,creating a kilometer-wide depression in Arizona.


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Large impacts are rare now, but were much more common during the earlyhistory of our solar system when the space debris was being swept up. Thesurfaces of Mercury, the Moon, and Mars are covered with impact craters,most of which scientists believe formed during the first half billion years of

solar system formation. Earth also has several impact craters on its surface,some quite large. One of the most famous and destructive impactsbelieved to have occurred took place about 65 million years ago. A meteroid,1016 kilometers in diameter, struck Earth near what is now the YucatnPeninsula of Mexico. This impact is thought to have triggered global firesand tsunamis and created a cloud of dust and water vapor that enveloped theEarth in a matter of days, resulting in fluctuating global climate changes. Theextreme environmental shifts are believed to have caused a mass extinction of75% of Earths species, including the dinosaurs.

Where Do We Find Meteorites?

Meteorites are fairly indiscriminate about wherethey land. They fall everywhere on Earth. Findingthem is the challenge! A little more than two-thirdsof Earth is covered by water; locating a meteoriteon the deep sea floor is difficult, to say the least.

Meteorites also fall in unpopulated regions andplaces that are difficult to reach. There are a few places where scientistsconcentrate their efforts because the meteorites are easier to find. Desertareas are not covered by vegetation, and meteorites differ from the

background. Many meteorite expeditions in the deserts of Africa andAustralia have increased the collections under study. There is one desert thathas provided the most meteoritesthe polar desert of Antarctica! There areseveral reasons why Antarctica is such a spectacular collecting place. Thefirst is that the dark meteorites are easy to see against the white ice! In

addition, meteorites do not break down as quickly in the frozen, dryatmosphere. The movement of the ice covering Antarctica also helps in thesearch for meteorites. Meteorites that land on the surface of the ice sheet arecarried along by the ice flow. There are locations where mountains act as a

barrier to ice movement. The ice flows up along this barrier and is sublimatedevaporatedby the fast dry winds of Antarctica. The meteorites do not


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evaporate they are left behind. This process of ice flow and sublimationhas continued for thousands of years, concentrating the meteorites intodistinct patches. Collecting expeditions in Antarctica have nearly doubled thenumber of meteorite finds in the world.


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Effects of Space on the Human Body

On Earth and in space we must maintain our health to perform our everydaytasks wellfrom homework to playing ball to mowing the lawn to building

a space station. We need to eat well, exercise, stay clean, get enough sleep,relax, avoid too much sun, and more! While there are many commonalitiesfor staying healthy shared by children and astronauts, living and working inspace puts some unique twists on health issues.

Eat Right!

Eating well-balanced diets contributes to our physical and mental health.According to KidsHealth, each day 913 year old girls need:

5 ounce equivalents of grain, such as a cup of cereal(boys need 6 ounces);2 cups of veggies (boys need 2 cups);1 cups of fruit;3 cups of milk (or another calcium-rich food);5 ounce equivalents of meat, beans, fish, and nuts;6 to 8 glasses of water;

So is junk food allowed? You bet! Dr. Scott Smith, the leader of theNutritional Biochemistry Laboratory at NASA's Johnson Space Center says,"You can eat any food in moderation! You just need to be sure that you aregetting a balance of different foods." Astronauts take some special things toeat on board the spacecraft. Favorites include M&Ms, candy bars, and beef

jerky. Even astronauts get the munchies!

Astronauts need well-balanced diets as well, but they face some specialchallenges caused by changes in the way their bodies function in space.


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Expedition Science Officer Ed Lu uses chopsticks to hold a piece of food andwith a drink packet floating in front of him.

Getting Enough to Eat. Many astronauts find that they are just not as hungryor the food is not as appetizing, or they are too busy to eat when they are inspace (sound like familiar Earth-based excuses?!). Most lose about 5% oftheir weight during a typical Space Station stay of 4 to 6 months. While notlife threatening at these levels, they are encouraged by the medical team to

eat balanced meals even when they are not hungry, and to eat higher caloriefoods. To help ensure appetizing menus, well before blasting off into space,the astronauts taste-test the food and select their personal menus. Menuselections help design meals that are balanced with the needed amount ofvitamins, minerals and calories.

Wanted: Calcium. Our bones form the support structure of our bodies. Theyprotect our organs, help us to move around, store minerals, and produceblood cells. Our bone is living material made of cells and organic materialsand more than half is made of calcium and phosphorous. Bones are our

body's "calcium bank;" calcium is constantly being taken out (resorbed) fromthe bones to use for other bodily processes. There is a constant balance ofosteoblasts, the bone-forming cells, and osteoclasts, the bone resorbing cells,and osteocytes, the bone maintaining cells. We need to consume lots ofcalcium to maintain healthy bones, and keep the activity of these three cellsin balance.


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Under microgravity conditions, calcium becomes even more importantbecause our bodies have no reason to maintain such a robust skeleton; lesssupport is needed when we are not experiencing the pull of Earth's gravity. Inspace, the lack of gravity signals the osteoclasts to begin breaking down the

unnecessary bone and the osteoblasts either don't change or slow theirproduction of new bone. The net result is for a loss of bone mineral.

Astronauts lose 1 to 2% of their bone mass for each month they are in space.This means that they lose 10% of their bone mass in less than a year onEarth, humans lose 10% of their bone mass after the age of 50 and over a

period of 10 years!

Bone mass losson Earth or in spacemeans that bones become weaker

and they fracture and break more easily when stressed. To make thechallenge to health even more complex, that calcium can be depositedelsewhere in the body and cause problems like kidney stones. To counter

bone mass loss, astronauts eat a diet rich in calcium.

Once the astronauts return to Earth the bone loss stops. Scientists are workingto understand if the lost bone is completely replaced and if the new bone isthe same strength or weaker than the original. Because space travel has beenlimited to relatively short visits the longest has been about 14 months

we are still working to understand the impact on the human body. NASA istesting new exercise equipment and routines, nutrition, medications, andother ways to help to combat the changes to the human body in space.


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Flight Engineers Cosmonaut Sergei Treschev (left) and Astronaut Peggy

Whitson stand around table in the galley area on the International Space

Station preparing a well balanced meal of hamburgers. Hands-free dining!

Vitamin D Dilemma. On Earth our skin uses small amounts of naturalultraviolet radiation to manufacture vitamin D, which like calcium isvital to maintaining healthy bones. About 10 minutes of Sun each day allows

our skin to make the recommended amount of vitamin D. Going outside toget a little sunshine on their bodies is not a possibility for astronauts! In fact,because they are above Earth's atmosphere, they are exposed to much moredangerous levels of ultraviolet and other radiation from the Sun than we areon Earth's surface. To work outside in the space environment, astronauts haveto wear space suits. In addition to providing life support, the suits also serveto cover their bodies and shield them from ultraviolet radiation. Their spacehelmets are equipped with special visors that filter out ultraviolet radiationand protect their eyes. So, back to the vitamin D issue because astronauts

cannot produce vitamin D naturally from sun exposure, they takesupplements to help with this issue. NASA scientists are preparing a study atthe South Pole to investigate what amount of supplement is required forindividuals spending months without ultraviolet light exposure.

Iron in the Extreme: Astronauts accumulate iron in their body; likely relatedto a few causes. Upon entering weightlessness, the body begins to reduce the


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number of red blood cells and the volume of blood in the circulation, perhapsbecause it is easier to pump blood through the body in microgravityconditions. The iron from the excess blood samples is stored in places likethe liver. Too much iron can be harmful, and reducing the amount of iron in

the body is hard as typically (on Earth) the body struggles to get enoughiron.

Fabulous Folate: Folate is an important vitamin, and among other functions,it helps to repair cellular damage from high energy solar radiation and fromthe pure oxygen astronauts breathe at times during their flight (such as duringspace walks). Astronauts eat diets rich in folate.but there are concerns thatthe vitamins in food may not be stable in the radiation environment.

Healthy Hydration: Water makes up about 2/3 of our weight. Our cells needwater to create the chemical reactions that sustain us, and water in our bloodhelps our circulatory system carry nutrients. Water helps to carry toxins outof our bodies. Everyone including astronauts loses water when theysweat, go to the bathroom, and even when they breathe. Astronauts, likechildren on Earth, have to drink lots of water to keep their bodies functioningwell. Six to 8 glasses of water are recommended for children and astronautseach day.

Exercise!Exercise keeps our heart healthy, makes our muscles and bones stronger,keeps us flexible, and makes us feel better all around. On Earth, gravity pullsagainst us when we walk, run, and play ball this makes our muscles workhardand keeps them strong! It also stresses our bones and tells our bonecells to continue to make more bone. But in space, astronauts float aroundand don't have to use their muscles nearly as much and they don't need their

bones to help support them. On the Space Station objects have no weight and little effort is required to lift things or move around. Standing, walking,

and even breathing on Earth requires more muscle and bone strength than inspace.

Because astronauts don't need as much muscle and bone in space, their bodystops maintaining themtheir muscles atrophy (even their heart muscles getsmaller because the heart does not have to pump as hard in microgravity) andtheir bones deteriorate. Astronauts have to exercise almost 2 hours a day!


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to make their muscles and bones physically work and stay healthy for theirreturn to Earth.

Astronaut Peggy Whitson exercises during her stay aboard the International

Space Station.

What kind of exercises do astronauts do? They perform "resistive" exercises;they pull against the exercise machines in various ways making it seemlike they are lifting weights with their arms and legs. They also pedal on a

recumbent stationary bicycle and walk and run on a treadmill. The bicycleand treadmill can be programmed to provide resistance to their pedaling orwalking, so they get quite a workout even in microgravity. Astronauts alwayshave to be attached to the machines to keep from floating away! Evenwith this much exercise, astronauts still experience muscle and bone loss andhave to build their muscles when they are back home.


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Astronaut Charlie Hobaugh performing exercise on the iRED on the KC-135.

Special exercise equipment is needed in the microgravity environment aboard

the International Space Station. Regular weights are "weightless" in space;exercise equipment is designed to resist lifting and pulling and pushing so

that astronauts can get a healthy workout and maintain their muscles and

bones.

On Earth, we also need to exercise to maintain healthy and strong musclesand bones. If you stay in bed for a long time a month or more whenyou finally get out, your muscles are very weak and you will tire quickly. So

stay active!Stay Clean!

Staying clean helps to prevent the spread of germs and diseases at home orin space. On Earth, this means bathing, washing our hands, brushing ourteeth, and wiping dirty surfaces with disinfectant. In space, it means the samething, only different ways to do so! You cannot have free-flowing water inspace; in microgravity, the water does not simply flow down the drain!Astronauts use sanitizing wipes to keep their bodies and hands clean. Theyuse rinse-less shampoo to wash their hair; just rub it in and towel it off! To

brush their teeth astronauts can either swallow the toothpaste (yuck) or spit itinto a wipe or cloth. Dishes and surfaces are cleaned with sanitizing wipes.


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NASA/Mir-23 researcher Jerry Linenger brushes his teeth while otherpersonal hygiene items float around him - including toothpaste, deodorant,

brush and Astro gel.

Sleep Well!

Getting plenty of sleep helps our bodies to rest and recover from activity andkeeps our brains thinking clearly when we are awake. Eight hours is therecommended number of hours of sleep each day for children and for

astronauts! However, children often are tucked into their beds and astronautsarestrapped into theirs. In microgravity astronauts float; their movementsneed to be restricted so that they do not bump into places they shouldn't. Likeon Earth, it can be hard to get a full 8 hours of sleep in space. For starters, itis rather exciting to be in space and who wants to miss the adventure bysleeping through it?! Daylight is also an issue; because the Space Station isgoing around Earth at a high rate of speed, the Sun rises every 90 minutes.This pattern of darkness and sunlight can be disruptive to sleep; astronauts

pack sleep masks. Physical changes that the astronauts' bodies go through in

space lengthening of their spines, shifting of their fluids can causediscomfort that prohibits sleep as well. And finally, sometimes the jobunderway requires the crew to work shifts; it's hard to sleep when your teammates are banging around and talking! Once the astronauts are back on Earth,their sleep patterns return to normal.


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Astronauts Frederick Sturckow (top), pilot, and Jerry Ross, missionspecialist, strap themselves into sleeping bags to prevent themselves from

floating around the Space Shuttle while they snooze.

Stand on Your Head!


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Astronaut Leroy Chiao, Mission Commander, has a thinner face before

traveling into space.

Not really. On Earth, our blood tends to go toward our feet because of thepull of gravity. Our strong heart muscle keeps the blood circulating. Inmicrogravity, however, our internal fluids those in our cells and blood shift from our legs toward our heads. Astronauts suffer from shrunken legsand puffy heads very soon after going into space. This can cause headachesand stuffy heads.

Astronauts also grow taller! Our spines backbones are made of 33vertebrae that are separated by thin pads of tough fiber (inter-vertebral discs).

This inter-layering of bone and disk allows our spines to be flexiblelettingus bend and twist, but still protecting the important nerves in our spinal cord.Earth's gravitational force compresses our spines; we do not sense thecompression because we are used to it. But in microgravity settings thiscompressive force is no longer present and our spines stretch! Astronautsactually grow 2 to 3 inches taller (5 to 8 centimeters) when they are in space!The stretching can cause them some pain; many astronauts have back painwhile they are in space and the stretching can potentially injure nerves.

Expedition 10 Crewmembers onboard the International Space Station.

Astronaut Leroy Chiao sits in the front on the left. Living in the microgravity


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environment of the Space Station has caused fluid to shift to the astronauts

faces and upper bodies, making them look "puffy."Their faces will return to normal when they are back on Earth.

Unfortunately, there is little that can be done for any of these conditions from swollen heads to increased height; astronauts just have to tough it outuntil they get back to Earth and the conditions go away.

Stay Balanced!

On Earth we know where "down" is. You fall there. In microgravity,however, there is no "up" or "down." Our inner ear contains tiny "motiondetectors" that along with information from our eyes, ears, and skin send signals to our brain about our condition of motion and balance. Withouta key, such as "down," our sensitive systems have a difficult time sensing ourorientation. Indeed, astronauts often feel disoriented and upside down theyare suffering from "space adaptation syndrome." Many astronauts havenausea, vomiting, and headaches that disappear after the first few days ofspace travel.

Use Sun Block!

Our Sun provides heat and lightthings we need and enjoy on Earth! But italso produces other types of energy, some of which is dangerous to humansand other organisms because it can damage our tissue. Much not allofthis dangerous radiation is filtered by our atmosphere. Some ultravioletradiation passes through our atmosphere. While we cannot see or feel thisultraviolet energy, it interacts with our tissue. On the plus side, it helps ourskin manufacture vitamin D, a necessary vitamin for bone production andimmune system health. However, too much ultraviolet radiation causes ourskin to burn. On Earth, we can protect ourselves by wearing clothing, usingsun block, and staying out of the Sun.

Astronauts work above Earth's protective atmosphere and are exposed to highlevels of ultraviolet radiation and other radiation such as high energy X-rays,and gamma-rays and even more dangerous cosmic rays. Ultraviolet radiation


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is not as much of a concern; they work in spacecraft that have specialshielding, wear special suits when they work outside of the spaceship, andeven have special visors to protect their eyes. This equipment has been coatedwith special UV-blockers.

Astronaut James H. Newman, holds one of the hand rails on the Unity

connecting module during the early stages of a 7-hour spacewalk. The

astronaut is protected from harmful ultraviolet radiation by the spacesuit and

specially coated visor on the helmet. The spacecraft also protects the

astronauts from some of the radiation in space.

However, some high energy radiation can still pass through the shielding.Astronauts receive 10x the amount of radiation exposure as we do on Earth.Such high exposure can damage the immune system, causing astronauts to besusceptible to infection while in space. Long-term exposure can damage cellsand DNA, leading to cataracts and cancers. Astronauts wear instruments,called dosimeters, that monitor how much radiation each of them has

received. Once they reach certain levels, they do not continue to work inspace. NASA and other space agencies are exploring the effects of radiationand testing different materials that may be used in suits and spacecraft to

protect space travelers from radiation.


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Cosmonaut Sergei K. Krikalev (left) and astronaut John L. Phillips, NASA

Space Station science officer and flight engineer, examine an European

Space Agency radiation experiment aboard the International Space Station.

The experiment is designed to help scientists understand the exposure of

astronauts, including those making spacewalks, to radiation. The human-torso-like device was retrieved from the exterior of the station.

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