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396A Posssibility of Asteroid Hitting Earth (1)
396B Posssibility of Asteroid Hitting Earth (2)

366. The 2011-2 sunspot maximum

I watched this show on the Discovery network about sun storms and it left me a little scared. It was about the effects it could have on earth and all the damages it can cause. The picture they painted was apocalyptic. Should we be worried about the 24th solar cycle when it reaches its maximum around 2011 or 2012? What could happen to the earth and to us? I would appreciate your answer.

Reply

The sunspot cycle has marginal effects on life on Earth. One important effect is higher flux of soft X-rays, which heats the upper atmosphere and expands it, causing faster decay in the orbits of low-altitude satellites. The effect on cosmic rays amounts to a few percent (depending on what is measured) and big magnetic storms are few, random and if they prefer any time, it is a few years past the maximum

I have not seen the "Discovery" program, but anything beyond the above is probably unscientific. The next cycle is predicted to have a high peak

http://www.ucar.edu/news/releases/2006/sunspot.shtml

but not as high as the peak observed during the international geophysical year (IGY) in 1957-8.

There have been some wild rumors (in the public and in some TV programs) predicting a catastrophe in the year 2012, at the end of the large cycle of the Maya calendar. I have received many inquiries about that, and some are linked from the end of

http://www.phy6.org/stargaze/Scalend.htm

http://www.phy6.org/Education/weather.html

http://www.phy6.org/earthmag/demagint.htm

367. Is Earth adding mass?

Is the mass of the Earth increasing? I wonder when I read about ancient cities being excavated under tons of earth. Is this top layer accumulated from space debris or simply existing matter displaced from other areas of the Earth? The Grand Canyon is another example. The different layers of the canyon walls relate to different time periods, was the circumference of the Earth smaller at these earlier geological periods? If the Earth is accumulating more mass how will this effect our orbit around the Sun?

Reply

I doubt the mass is changing significantly--if it did, that might show up in the rotation period of Earth, which is monitored very closely (enough to track changes due to tides caused by the Moon's and Sun's gravity).

Buried cities are often covered by wind-blown soil (and sometimes by their own debris, as earthquakes, wars and storms destroy buildings and people later build on top of the rubble).

The Grand Canyon eroded gradually, and the debris was swept downstream. Right now its path is blocked by big dams, and it is estimated these will silt up in a couple of centuries (as would other dams world-wide, e.g. the "High Dam" in Aswan, on the Nile in Egypt).

The San Juan River in Utah flows into the Grand Canyon and has carved an impressive canyon of its own (search "Goosenecks of the San Juan"). The interesting feature is that this canyon twists like a snake. Such twisting is often seen in shallow flood plains (e.g. of the Mississippi) and is caused by the curvature eroding its outer curve and depositing silt on the inside. The San Juan must have been a shallow river when those "goosenecks" were first created, then the land gradually lifted and the river bed dug in. The Grand Canyon is similarly believed to have arisen by the gradual lifting of the surrounding land. Other land of course may sink (e.g. Central Valley in California), though overall, the earth's mass stays more or less the same (but yes, there are meteorites arriving).

368. Shape of a "bottle rocket"

It is hard to reach my question without putting in my theory. I believe that a bottle rocket has a pointed tip for many reasons. I think that a rocket with a pointed tip goes easier through the air than one that is blunt. . . . . I've put into play Newton's laws but this is what I want to know: are there any other things that effect why a pointed tip is better than a blunt tip on a bottle rocket? I would like to include that the rocket is stabilized with wings "similar" to a trapezoid shape (as an example trapezoid is usually used in textbooks. Here is a similarity to what I mean: /=\ ).

Reply

Shock waves are not involved in a bottle rocket, but its motion follows simple conservation of momentum ("Stargazers" section 18b), which itself is a consequence of Newton's laws of motion. In general, I would advise you to study those sections (from 13 to 21, at least)--though if you are a high school senior, you probably will have other things to worry about.

The shape of the bottle rocket and the nose cone and fins are mostly designed to give it stability, so that it does not turn sideways. Its speed is so slow that air resistance is not much affected by the sharpness of its front end. Even airliners that fly at 600 mph have rounded fronts, allowing the air to divide smoothly. At low speed, air resistance actually depends more on the shape of the rear. If the shape is fishlike, closing smoothly in the rear, the air flow also closes smoothly and its pressure on the rear balances the pressure on the front. If the rear is suddenly cut off like a box (as in big trucks), air swirls around and those swirls have less pressure, so extra energy is needed to overcome the difference in pressure between front and back.

Everything changes when one passes the speed of sound--about 1000 feet per second in air. At such speeds air cannot move fast enough to get out of the way and is compressed in a way that heats is. Such heating creates a serious energy loss which cannot be recovered by anything happening in the rear, so resistance becomes much higher. Space rockets and bullets have sharp tips to reduce the region where air is compressed, and that reduces the loss of energy to shock formation. On the other hand, the reentry capsule of Apollo astronauts was wide in front to create a big shock and help the capsule start losing energy and speed even high up where the air is still very rarefied. It all depends on what you want!

369. Fantasy spaceflight vs. reality

A question that keeps burning in my head is: why don't we have interplanetary/stellar ships yet? I watch TV shows like Stargate SG1/Atlantis and Babylon 5 and ask myself why have'nt we got there yet? I mean on "Stargate" their first ship was during 2002-2004 and looks fairly easy to construct using resources we have here already. So I wonder, why don't we have star ships, are we capable of doing so?

Reply

Video shows may present beautiful illusions--people flying, reading thoughts, sensing the future... but that does not mean they are possible. Sending people to Mars takes awesome rocket power, much beyond what we have (even if we had a good reason to do so), and I calculated such a flight on my web site.

Even the Apollo landing on the Moon was a near-miracle. Have you watched on TV pole vaulting (as you may do at the coming Olympic games)? An athlete run towards a hurdle holding a long pole ahead, sticks it in the ground at the proper spot and flies high in the air. If he is lucky and fast enough, he skims half an inch above the hurdle without touching it, before falling down onto a big cushion. His jump is just barely possible--like the Apollo landing--and even then, it may fail, like the flight of Apollo 13. All spaceflight is barely possible! Hollywood stimulates our imagination by staging feats which are clearly beyond what we are capable of now (or sometimes, ever): enjoy those shows, but don't confuse them with reality!

370. Telling a 7-year old about stars "dying"

... few days ago, after having fun looking at stars in the night over our homeplace in Casalecchio di Reno (Bologna - Italy), I tried to explain to my 7 years old daughter the clear idea (... clear to me), that the star we're looking at, just now, ... maybe is already dead, since a long time ago.

She didn't really understand very well the fact, ... so since then she asks me every day to explain again and again, why stars die, why I can see light, ... from something which is already switched off, ...??

Can you help me, also with suggestion of book about Astronomy for children?

Reply

Hello, Marco

Maybe the word "dead" confuses your daughter. The star is still there, but its "fire" has gone out, after using up all its fuel, in the time taken for its light to reach us. Similarly, when the NASA "Phoenix" landed on Mars, yesterday or the day before, it took 15 minutes before Earth received the information.

Any book for your daughter should be in Italian (although she can read an Italian translation of my web pages). I suggest you contact an amateur astronomy club near you--there exist 178 in Italy.

371. (1) Why is lightning jagged? (2) What did Tesla do?

How are you and thanks for the information, I signed as James Joule but my real name is (given) . I'm an electrician from Sheffield England, I've always called myself James on the internet because they say not to put your real name out there, and I admire the chap so I borrowed his name. I spent 4 years at college and did just enough to pass (I had other things on my mind in those days), we studied Maxwell's equations very briefly but Tesla was never mentioned. I have 3 sons who are all now qualified electricians, I asked them if they had ever heard of him and none of them had, I couldn't understand why after all he accomplished and that's why I started to research his work and anything to do with electricity no matter how obscure. I am now out of control, I can't stop learning, there are too many unanswered questions; I'm not trying to solve the energy crisis, I just don't like things that I can't understand.

Another question: if electricity takes the easiest path, why doesn't a bolt of lightning strike in a dead straight line to earth?

Reply

Hello Marc

Take a newspaper page which has not been folded and rip it apart by pulling the two sides. It almost always tears along an irregular line, not a straight one. Why? When your pull gets strong enough (especially if the pulls of the two hands are not exactly opposed), somewhere the edge of the paper will tear, and the tear will then advance across the page. However, the advance of the tear does not depend on the shape of the part of the tear already existing, only on the forces at the tip of the tear. These generally advance across the page, but may slant this way or that, depending on the way tension is distributed across the page, and maybe also on the alignment of the fibers.

It is similar in lightning. The top of a thunderstorm cloud is usually charged positive, and the bottom (and ground) are negative in comparison to it--creating a certain electric tension, a voltage drop. In an electric conductor, a voltage drop causes a current to flow. Air, however is an insulator, allowing the voltage to build up, to millions of volts.

However, as you surely know, even an insulator can "break down" when the voltage drop is large enough to tear some electrons off their atoms. Strictly speaking, it is the electric field E which does it, a vector with direction, because the force on an electric charge q is Eq; E itself is the rate at which the voltage V drops off, its magnitude is dV/dx with x in the direction in which V varies most, and its full value (you studied Maxwell's equations once, no?) is –gradV (the minus because the force is from high voltage to low).

If the voltage drop across the cloud is uniform, the air insulation will contain it. If however some of it is concentrated somewhere (influenced by the distribution of updraft winds which

create the voltage

leader of the stroke

stepped leader

As for Tesla...

http://www.phy6.org/Education/FAQs8.html#q123

372. How can the north wall of my house be in sunlight?

I read an article you wrote on NASA's site entitled

The Angle of the Sun's Rays

Reply

greatest distance from the horizon

rises to the north of east

north of west

373. Heating the inside of Earth

Reviewing your article on the earth's magnetic field (

http://www.phy6.org/earthmag/dynamos2.htm

Reply

Heat is a form of energy

Stars

done with shrinking

http://www.phy6.org/stargaze/Siomoons.htm

Mainly radioactivity

http://www.phy6.org/earthmag/magnQ&A4.htm#q60

374. Dawning of the Age of Aquarius

I have a question about the age of Aquarius, the

precession explanation

Reply

http://www.phy6.org/stargaze/StarFAQ5.htm#q91

375. Why is hydrogen the fuel of choice?

I was looking over your question and reply segment of your web site and a physics question came to mind. Why is hydrogen the most selected medium for fuel cells. I am probably missing something but if the objective is to strip electrons from the hydrogen atoms, would a more electron-rich element provide more energy in a smaller package, for example calcium.

Reply

Your question involves chemistry, which is not my field, but please realize that the binding energy of all electrons is not equal.

Looking just at the stripping of electrons, hydrogen certainly has two big advantages over calcium. First, it is lighter--most of the mass of the hydrogen atom is that of its proton, while calcium contains about an equal number of neutrons, which bind no electrons and just add weight. Second (and probably much more important), only the outermost electrons play a role in chemical reactions. Electrons closer to the nucleus are too tightly bound to do that, though the protons that bind them still add mass.

376. Gamma ray bursts

I was wondering if you could explain to me what gamma ray bursts are? I've read various things about them but I can't really get the gist of it...I understand that some think such a burst may have affected Earth in the past...could this happen again?

Reply

If gamma rays had not been observed, I doubt anyone would have predicted them, and even now a lot of them is not understood. I wrote about them in

http://www.phy6.org/Education/wenpart2.html

http://www.phy6.org/stargaze/Sblkhole.htm

http://apod.nasa.gov/apod/ap080613.html

377. Counter-clockwise swirling motion in the atmosphere

(From a physics teachers' listserve)
Pressure is a scalar [not a vector--it has magnitude but no direction] I don't see how a scalar can produce any chiral [swirling] effect (clockwise OR counterclockwise). The force on the air comes from a pressure gradient which is a vector, but it is a curl-free vector field (funny thing about gradients) and I don't see how such a field could produce a chiral effect either.

Reply

Some of what appears below contains guesswork. If there is any error, I would like to be at least the second person to know, so please tell if you spot one.

Fluid motions can be divided into two classes: solenoidal (swirling) and irrotational (pressure related, associated with sources and sinks). There exist some ambiguous flows which can be assigned to either class, but they are a special group (source-free flows) and I suspect they can only be defined within regions of space with closed boundaries.

The classification is explained in high school terms in

http://www.phy6.org/Education/wEMinduc1.html

in the last part of that web page titled "Background Concept: Vector Fields"

I suspect that atmospheric flows are basically solenoidal--swirling--and that areas of higher and lower pressure--so popular among weather forecasters--are but a secondary manifestation. They are simple indications of what the large scale flow is doing--and useful, too, since barometers are cheap, and they make local observations of pressure easy. However, local pressure is just a simple way of guessing the large-scale flow pattern, which is the real origin of weather phenomena.

The large-scale pattern is solenoidal, but it is NOT just swirling around low pressure areas. Instead, it has a global scale, going around the globe--from west to east in middle latitudes, from east to west near the equator. What creates the low pressure areas at middle latitudes are those big waves in the global flow (the weatherman says "in the jetstream" but that is because the jetstream is the fast-moving core of the global wind and thus a good indication of the location of its center). They are known as Rossby waves, and they help spread heat from equatorial latitudes to middle latitudes, involving a larger area of Earth in the return of solar heat to space.

I wrote about that in

http://www.phy6.org/stargaze/Sweather2.htm

378. Leap years on the Jewish calendar

Please inform me if you can direct my search for an index with the Jewish leap years for the 20th century and the start of this one.

For some reason, my internet searches are not proving successful.

Reply

The Jewish calendar goes by 19-year cycles--the calendar year 2008 is numbered 5768 and at the end of September 5769 begins. The current cycle is #304 and began in 5757 (5757:19=303 with no remainder).

Each cycle contains 7 leap years--numbers 3, 6, 8,11, 14, 17 and 19 of the cycle (19 at the start of the next cycle). The number 5768 leaves a remainder 11 when divided by 19 and is therefore a leap year. The year 5769 leaves a remainder 12 and isn't. The calendar has additional adjustments to prevent, say, the Day of Atonement (Yom Kippur) from falling on Friday or Sunday, creating too much strain over a two-day period.

379. Earth axis tilt and climate (1)

What would happen if the earth's axis was changed, for instance, if it went from being tilted to being straight up [perpendicular to the plane of the

ecliptic].

Reply

380. Earth axis tilt and climate (2)

Is the Earth's Tilt increasing?

I recently learned (from my mother - and I ALWAYS believe my mom) that the Navajo tribe (in northern Arizona) believes in global warming. The medicine men state that the Earth's tilt has increased. They say that the sun is rising further north than it has traditionally and the star alignment has changed. Thus, the Navajo believe that this is causing greater solar exposure at the poles, resulting in the rising temperatures.

Reply

The observed shifts in tilt angle are of order 0.1 degree or less, due to disturbance of Earth's motion by gravity of the Moon, etc. That gravity does cause the pole of the heavens to rotate slowly around a large circle, as someone has already written to you, and it causes slow changes in the stars seen in the night sky, on any given date. A good simple discussion is at

http://www.phy6.org/stargaze/Sprecess.htm

equal amount of heat

http://www.phy6.org/stargaze/StarFAQ13.htm#q207

http://www.phy6.org/stargaze/StarFAQ19.htm#q338

381. Does the Sun move?

I am working as a high school teacher in Mysore, South India . I got a glimpse of your site StarFAQs. It was very useful. Thanks, but I have a question not answered there.

Does the Sun move ? If so what is its path ?

I would be much obliged to have a reply .

Reply

Any motion is relative to something. You walk inside an airliner: what are you moving relative to? Relative to your seat, you may be moving at 1 meter/second. Relative to the ground, you maybe moving at 250 meter/second. Relative to the Moon it is again different, because you are attached to a rotating Earth (and the Moon also moves). And so on .

In "classical" mechanics, you can always add a CONSTANT velocity (constant in direction and speed) to any motion and the result will still be correct--any velocity is just derived relative to a different point, one which movies with a different constant velocity. It is a fact of the universe ("the principle of relativity") that no matter where the point is chosen, you get the same physics.

On the other hand, classical mechanics gives a definite velocity to motion with acceleration (to which any constant velocity can be added). In a car moving around a curve or coming to a sudden stop, acceleration occurs, as determined by the motion, related to the forces which control the motion.

The Sun definitely accelerates, but again we can ask, relative to what should we calculate its motion? Inside the solar system, it is not true that Earth orbits the center of the Sun; it orbits the center of gravity (CG) of the Sun-Earth system, which is close to the Sun's center (because the Sun is much heavier). See

http://www.phy6.org/stargaze/Srocket.htm

other planets

CG of the solar system itself

http://www.phy6.org/stargaze/Sun4Adop3.htm

Solar Apex.

expansion of the universe

382. Can the Sun interfere with the visibility of the Great Dipper??

If the earth rotates around the sun as suggested, how is it possible that we can see the same star constellations in the sky all year round? It does not sound possible. If I can see the Big Dipper during the summer months, then it should be hidden by the sun during the winter months, right?

Reply

Depends on the location of the constellation! As explained in section #2 of "Stargazers," as the Earth circles the Sun once a year, the position of the Sun in the sky, on the background of distant stars, traces a circular path, covering--depending on date--all directions in the orbital plane of the Earth (see second image in that section). Any constellation located on that path will occupy the same direction as the Sun at some time of the year, and at that time cannot be easily observed. There exist 12 constellations like this, a group also known as the zodiac. Thus Scorpio is high in the sky in mid-summer but may be near the position of the Sun sometime in winter.

On the other hand, constellations located FAR from the ecliptic on the celestial map will never be in the direction of the Sun. The north pole of the ecliptic is in the constellation Draco, only 23.5 degrees from the celestial pole (the direction of the Earth axis). The big Dipper is in the same neighborhood, and its direction is therefore NEVER visited by the Sun. Sunlight may make it invisible to the eye in the daytime, but even then it is above the horizon enough hours at night.

383. Why can't we feel the Earth's rotation?

Why does a human feel stable. although Earth rotates?? I mean, how come we rotate with the Earth but feel no motion??

Reply

Forces are associated with acceleration. If you ride a car on a smooth road at constant speed and fixed direction, your motion exerts no force on you and you will feel as if you were not moving at all. The car's engine is needed to overcome friction of the road and air resistance, but inside the closed car you feel force-free.

Motion in a circle is accelerated (section #19 in "stargazers"), and an object will NOT move in a circle unless some force maintains the acceleration. But how big a force? The formula in section #19 tells you how big: the faster the rotation (turns per second, say) the greater it is, and the radius of the circle also figures

. The Earth's rotation definitely exerts a force on you, but you don't feel it because it is small, a fraction of 1% compared to your weight (sect #24a). So the force responsible for your motion is hidden by the much greater force of gravity, making gravity appear a little stronger in some places and a little weaker in others. It can be observed by comparing the speed of pendulum clocks, which respond to the total downward force at their locations, and this was already done In the 1600s.

Some hotels have fancy restaurants sitting on turntables on top of the roof, with windows all around (entrances are all in a small tower in the middle). They take something like half an hour to go around, and because the rotation is so slow and smooth, you don't feel it at all. I once ate at such a restaurant in Montreal, Canada, and all I felt was that the view from the window gradually changed.

384. Is our galaxy held together by a central black hole?

I would like to know if it's true to say that the black-hole at the center of the galaxy maintains the galaxy in its cohesion.

Reply

Actually, this is an area of astronomy poorly understood. There certainly exists a concentration of mass near the center of the galaxy, and we now know that some of that mass is concentrated in a giant black hole--see

http://www.phy6.org/stargaze/Sblkhole.htm

Kepler's 3rd law

http://www.phy6.org/stargaze/Sun4Adop3.htm

not the only factor

385. Why don't gas planets just evaporate?

A student of mine wanted to know why a gas giant planet didn't just evaporate off into space - I wasn't sure ! Can you help?

Reply

Because the planet's gravity holds the gas down! The student may just as well ask why our own atmosphere does not escape into space!

Of course, that gravity better be strong enough, because if gas molecules (energized by heat of sunlight) have enough speed, a weak gravity may not be able to hold onto them and they fly off anyway. As is the case with the Moon, Mercury and asteroids.

386. Source of the Sun's energy

I need help explaining to a 7th grade student where the sun gets its energy. I have read your website, and although I understand what you are saying, I am having trouble trying to explain it in terms a pre-teen would understand. I thought maybe you could condense what you wrote and give a few ideas on how to do this.

The question arose from our conversation surrounding The Law of Conservation of Energy. As always, my students try to find exceptions to the law. I love that they do this; however, they do ask questions that I find hard to explain. This is one of them. In the past, I have just given a general answer and moved on. However, teens are very perceptive and often know if someone is glossing over an answer or doesn't really know the answer. I know its okay to say "I don't know" to them, but I'd like to be a model of someone who seeks out things they don't understand.

Reply

Let me try, but we must start with some assumptions. It would take too much time and space to justify them.

The assumptions are that matter is made up of atoms, and each atom contains a nucleus with a positive electric charge, where most of the mass is concentrated, and lightweight negative electrons (thousands of times lighter), bound to them by electric attraction.

Also, that nuclei consist of two kinds of particles, very similar in mass and other properties--protons and neutrons. The difference is that protons are positively charged and neutrons are uncharged, and at least the smaller nuclei tend to have equal numbers of each, e.g. oxygen has 8 and 8.

Now if oxygen has 8 protons bound together in a tiny space, there must exist some specific nuclear force attracting them together--without it, the positive charges repel each other and the whole thing falls apart. (Again, the force between two protons or neutrons--or in a pair with one of each-- is about the same, while the "equal numbers" property is enforced by the "weak nuclear force" which need not bother us here).

Such facts were found by early nuclear accelerators, examining collisions between fast nuclei. The important thing is that the nuclear force (unlike the electric force) falls off rapidly with distance, so small nuclei (like helium, 2 + 2) are strongly bound and big ones like iron, much less strongly--protons and neutrons ("nucleons") of opposite sides of the nucleus are already distant enough to weaken the force.

In fact, iron is also less stable because all its positive protons repel each other electrically, and the electric force falls off more slowly with distance. If you could add nucleons to nuclei past iron, you would have to invest more energy to overcome electric repulsion than the energy added by nuclear attraction. By the time you reach the vicinity of uranium, nuclei tend to be unstable--that's why no heavier nuclei exist in nature, and even those close to uranium tend to break up gradually by radioactivity.

But with light nuclei like protons (=hydrogen nuclei), the nuclear attraction pulls them together powerfully. A lot of energy is released by combining protons to form helium, a "nuclear fusion" process (and to keep charge balance, some protons in this process change into neutrons plus positive electrons, which crash into negative ones and "annihilate"). That's apparently what happens in the core of the Sun, where the weight of all the mass piles on top is strong enough to hold the fusing particles together, at the high temperatures required by the process. Laboratory experiments have tried to keep fusion going in hot gas held together by strong magnets, but so far not enough energy is released to provide help ease our energy shortage. For more, see

http://www.phy6.org/stargaze/Sun7enrg.htm

http://www.phy6.org/stargaze/StarFAQ3.htm#q52

http://www.phy6.org/stargaze/Lsun7erg.htm

387. Point of gravity equilibrium

I am taking a Conceptual Integrated Science class (1 quarter) at ITT Tech. and we don't go very deep into any one branch of science, we just touch base in many, very quickly.

I am just curious if a spacecraft traveling from the Earth to the Moon can ever be pulled equally by the Earth and the Moon or if the gravity of the Earth will always remain stronger. I believe that at some point the gravitational pull must be equal but some of my classmates think the Earth's gravity will always be stronger. Please help us!

Reply

If you take the positions of the Earth and Moon at some moment and assume they are at rest at those points--then yes, there will exist some point in-between where their pulls are equal and opposite, canceling each other, and if you place a stone at that point, it will not fall in either direction.

In fact, however, everything moves. To simplify matters, let us ignore the Sun around which the system orbits, but assume the Earth is at rest, and the Moon orbits it in a near-circle. That stone will only be momentarily in equilibrium--as soon as the Moon moves away, the gravity of Earth predominates, though the pull of the departing Moon will pull it sideways to some extent. Because of the added sideways motion, the stone will not follow a straight line, but will end up in an elliptical orbit (perturbed by the Moon's gravity).

At whatever distance you place the stone, it will have its own "natural" orbital velocity around the Earth. Unfortunately, if the distance is less than that of the Moon, it will have a shorter period, move faster and again, pull away from equilibrium. There exists however one distance where the period is the SAME as that of the Moon, because the pull of the Moon subtracts from the pull of the Earth, and with less gravity, the stone moves more slowly.

The stone will then keep station with the Moon and stay in its place--if the Moon were small enough. That would be the Earth-Moon Lagrangian L1 point. I think it is not a practical orbital location, though certain orbits around it (halo orbits) could be.

There exists however an L1 point in the Sun Earth system, with similar properties, and it is in use. See

http://www.phy6.org/stargaze/Sorbit.htm

http://www.phy6.org/stargaze/Slagrang.htm

388. Solar system motion through the Galaxy

Hi, I'm from Mexico city and have several questions about climate changes.

Like the planets within a solar system, does our galaxy (or group of galaxies) turn around a bigger sun? If so, could that be considered as a cause for the weather changes the earth is experiencing?

I appreciate your answer. Thanks! Have a nice day

Reply

In one word, no. The sun with its system, with other stars of the Milky Way galaxy, slowly rotate around the center of the galaxy (for more about that, see

), but on the scale of the galaxy that motion is slow . More important, it is hard to see how the motion of the entire solar system could affect weather changes on Earth. Such changes depend only on what happens between Earth and Sun: the rate at which the Sun supplies us with heat (which varies only very little, by 0.1% perhaps) and the rate at which the Earth loses heat to space, which DOES depend sensitively on the atmospheric content of gases such as carbon dioxide and methane--see

http://www.phy6.org/stargaze/Sun1lite.htm

389. Spaceflight by waiting for the Earth to turn?

I have what seems like a simple question but I can't get a simple answer from anyone. Yours was one of the many websites I checked and it appeared to be the most thorough. I know you're busy, so I'll be brief.

Instead of flying within the earth's atmosphere, would it be possible to exit the earth's atmosphere, wait for the planet to rotate and then come back down when your destination reaches the point below you?

Example, I leave from a point on the equator. In space, I wait for the earth to rotate at 1400 mph and I return three hours later to a place 4200 miles away from my point of origin

Reply

No, this would not work. Going up and waiting is not a good way of traveling from one point on Earth to another.

Suppose you shoot a rocket vertically from the equator to an altitude of 1000 miles. It will fall right back! Not just that, but the velocity and momentum it has from rotating with the Earth is preserved. Because a point 1000 miles up is further away from the rotation axis, you need there a bit more speed to keep up with the rotation, so strictly speaking, it will lag somewhat behind the rotation and fall at a point some distance to the west.

And by the way, the velocity needed to reach 1000 miles may be enough (if you aim at angle) to reach 4200 miles away. I haven't calculated, but that is of the order of the range.

In any case, a spacecraft cannot just rise outside the atmosphere and wait. If it is not to fall back, it needs a velocity tangential to the surface of the Earth. If it is to stay up indefinitely, it needs an orbital velocity, circling the Earth in about 90 minutes (or more, for bigger orbits). That is about 24 times the speed of sound, so getting there requires an tremendous amount of fuel, and getting back an enormous amount of energy needs to be removed as heat, otherwise it will burn up in the atmosphere like "Columbia."

390. Does Earth rotation affect size of creatures?

My name is Ravi, I graduated in Canada. I read mostly all the questions and answers posted on your site. In fact, I was surfing to get answer to a question that popped up in my mind and I came across the site. The question is: "Does the rotating speed of earth has any effect on the size of the living creatures?" When dinosaurs walked on earth about 65 million years ago, I heard that they enjoyed 20 hours of day.

Reply

The size of creatures on Earth depends on effective gravity, including the centrifugal force associated with rotation. If gravity were stronger, creatures would be lower--assuming life were still possible.

The centrifugal force reduces effective gravity at the equator, but Earth rotates rather slowly and the effect is less than 1%. If Earth rotated faster, the effect would grow and the equator's radius would increase (see

http://www.phy6.org/stargaze/Srotfram1.htm

breaks up Earth

Mission of Gravity

391. The Year 2012

The end of the Mayan calendar, et al, notwithstanding, is the earth facing a potentially devastating phenomenon on the above captioned date, when the sun is aligned with the astronomical center of our galaxy?

I've heard everything from potential pole shifts to concern about the possible impact of a huge black hole, also located near the center of our galaxy. Can you offer any scientific, empirically based comfort here?

Reply

I keep getting more and more questions about 2012, and as far as I can see, there is no scientific foundation to any of those worries. Links to some answered questions (not all, by any means!) are given at the end of

http://www.phy6.org/stargaze/Scalend.htm

The Year of the Jackpot

392. Are our galactic arms winding up or opening up?

Which way do spiral galaxies rotate, are they rotating inward (winding up) or outward (winding out)?

Reply

I am not sure, but I think they rotate in the sense of winding up.

However, even if spiral arms look the way they would if they were pieces of flexible rope (say, floating on water), the way they form is not the same. When I was active in science, the leading theory was that they were formed as "density waves." See

http://en.wikipedia.org/wiki/Density_wave_theory

393. Advice to a home-schooling mother

I am a homeschooling mom developing a curriculum for my soon to be high schooler. What grades would you recommend this material to be used?

Reply

Homeschooling has great advantages and a possible disadvantage. The curriculum can be adapted to the interests of the student, and that is good (in moderation). However, the teacher may lack familiarity with some subjects, and teaching them then becomes a joint study, rather than guided expansion of knowledge with a knowledgeable guide.

About the first item--to what extent is your daughter or son interested in science and math? And related: (1) how fluent is that student in reading and in learning from a printed page? And (2) is the student also learning history, and liking it?

The related questions are relevant, because

(1) "Stargazers" is essentially an electronic book. No flashy pictures or videos, but a carefully worded exposition, leavened with tidbits of stories of technology and discovery.
(2) History serves as a framework; see for instance the timeline linked from the end of every sections. You will find there, in black print events from the history of the world, in red those relevant to the text, and in the latter, links to appropriate passages.

The ideas are further discussed in

http://www.phy6.org/stargaze/Steacher.htm

http://www.phy6.org/stargaze/Sarticle.htm

http://www.phy6.org/readfirst.htm

http://www.phy6.org/stargaze.zip

http://www.phy6.org/stargaze/Smath.htm

http://www.phy6.org/outreach/edu/standard.htm

http://www.phy6.org/stargaze/StarFAQ18.htm#q320

394. Are all stars we see suns?

By definition, are stars that we see at night are in fact all suns? Is a glowing star a sun?

Reply

The answer is "practically, yes."

There exist a few nebulae which may appear to be stars, though the telescope shows them to be more extended--the Orion nebula in the "sword" of Orion, part of our galaxy, the great nebula of Andromeda which is a nearby galaxy, and the two Magellanic clouds, small galaxies near ours.

Also, if you view the sky away from the Milky way with a very sensitive instrument, most "stars" you see are distant galaxies. See

http://www.phy.mtu.edu/apod/ap980607.html

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Author and Curator: Dr. David P. Stern
Mail to Dr.Stern: stargaze("at" symbol)phy6.org .

Last updated 11-21-2008 Edited 2 November 2016

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