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1681. The Sun--Introduction
... Astronomy index . Mechanics index . Sun index . ... The sections of "Stargazers" covering the Sun was an afterthought. The rest of the material was mostly complete when a teacher of astronomy, adapting the material for his course, pointed out an omission. ... Yes, indeed--and therefore this part was added. ... However, almost all the material on the Sun fits seamlessly into the sections that precede it or follow it, and lesson plans have been provided for sections #S-1 to #S-7 as well. ...
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Ссылки http://www.cosmos.ru/mirrors/stern/stargaze/Sunintro.htm -- 7.7 Кб -- 22.12.2007
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1682. "Get a Straight Answer"
... The ones included below are either of the sort that keeps coming up again and again, or else the answers make a special point, often going into details which might interest many users. ... About asteroids hitting Earth. ... Asymmetry of the Moon's orbit. Measuring distance from the Sun. ... The varying distance between Earth and Sun . ... How Tall Can People Get? ... I get . ... Radiation" is essentially something which spreads radially in all directions, along straight lines (in empty space). ...
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Ссылки http://www.cosmos.ru/mirrors/stern/stargaze/StarFAQ6.htm -- 64.6 Кб -- 22.12.2007
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1683. The Theory of Relativity
... Lesson plan (frames) . ... 22b. Relativity . ... By Newton's laws, two frames of reference moving with constant velocity relative to each other observe exactly the same physical behavior. There exists no way to tell, which of them is moving and which one is at rest: there is no "absolute rest frame" and no "absolute (constant) velocity. ... But for a while it seemed that by certain subtle effects, electromagnetic forces could distinguish whether a frame was in motion of not. ...
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Ссылки http://www.cosmos.ru/mirrors/stern/stargaze/Srelativ.htm -- 7.7 Кб -- 22.12.2007
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1684. Parallax
... Section M-7 describes the basic problem of trigonometry (drawing on the left): finding the distance to some far-away point C, given the directions at which C appears from the two ends of a measured baseline AB. ... That means that the angle ? ... 2? r covers an angle 360? . ... Suppose you want to estimate the distance to some distant landmark--e.g. a building, tree or water tower. ... Alpha Centauri, the sun-like star nearest to our solar system, has a distance of 4.3 years and a parallax of 0.75"....
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Ссылки http://www.cosmos.ru/mirrors/stern/stargaze/Sparalax.htm -- 13.1 Кб -- 22.12.2007
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1685. Spacecraft
... The first person to orbit the Earth was the Russian Yuri Gagarin, on April 12, 1961. The first American to do so was John Glenn, who completed three orbits on February 20, 1962; more than 26 years later, at age 77, Glenn returned to space aboard the space shuttle. ... Any manned mission faces the problem of safe return to Earth, which requires getting rid of the huge amount of energy associated with orbital motion. A spacecraft in low Earth orbit moves at about 24 times the velocity of sound. ...
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Ссылки http://www.cosmos.ru/mirrors/stern/stargaze/Spaccrft.htm -- 12.7 Кб -- 22.12.2007
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1686. Kepler's Third Law
... Kepler's 3rd Law . 21a.Applying 3rd Law . ... Besides the Moon, Earth now has many artificial satellites, put up by us earthlings for a variety of purposes. ... where for a satellite orbiting Earth at distance of one Earth radius R E , the constant k equals k=gR E 2 . ... The velocity for a circular Earth orbit at any other distance r is similarly calculated, but one must take into account that the force of gravity is weaker at greater distances, by a factor (R E / r) 2 . ...
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Ссылки http://www.cosmos.ru/mirrors/stern/stargaze/Skepl3rd.htm -- 11.7 Кб -- 22.12.2007
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1687. Frames of Reference: Loop-the-Loop
... 23a. The Centrifugal Force . ... You can also view this problem from the point of view of the outside world, using the centripetal force, but it is not as easy. At point A, on the top of the loop, both gravity and the centripetal force point downwards. ... A car going around a loop, with radius R and velocity V, is accelerating at a rate of V 2 /R towards the center (as long as it stays on the rails), and is therefore subject to a centripetal force mV 2 /R, also directed to the center. ...
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Ссылки http://www.cosmos.ru/mirrors/stern/stargaze/Sframes4.htm -- 9.0 Кб -- 22.12.2007
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1688. Frames of Reference: The Basics
... 22.Reference Frames . ... To derive the motion of a penny dropped inside an airliner moving at 600 miles/hr (about 1000 km/hr)--should we calculate it with respect to the interior of the airliner, or with respect to the ground? ... And if a similar penny is let go inside an orbiting spaceship--should its motion be calculated relative to the interior of the spaceship, or relative to the Earth outside? ... How do observations differ in the two frames--the airliner cabin and the Earth? ...
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Ссылки http://www.cosmos.ru/mirrors/stern/stargaze/Sframes1.htm -- 11.0 Кб -- 22.12.2007
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1689. The Path of the Sun, the Ecliptic
... The apparent path of the Sun across the sky. ... Like the planets, the Sun, too, moves around the zodiac, making one complete circuit each year. ... In one year, as the Earth completes a full circuit around the Sun (drawing above), the Earth-Sun line and its continuation past Earth sweep the entire plane. ... Since the Sun and Earth are in the plane of the ecliptic, the line is automatically in that plane too; if the moon is also on the same line, it must be in the plane of the ecliptic as well. ...
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Ссылки http://www.cosmos.ru/mirrors/stern/stargaze/Secliptc.htm -- 14.7 Кб -- 22.12.2007
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1690. Early Warning of Interplanetary Disturbances
... One possible application of a solar sail is a spacecraft to warn Earth of approaching interplanetary disturbances and shocks. ... Spacecraft that can provide such a warning are currently stationed at (or near) the Lagrangian L1 point , between the Earth and the Sun--at about 4 times the distance of the moon and 1/100 times that of the Sun. ... Because of the greater distance from Earth, the Earth's pull there is weaker, not enough to make the spacecraft match the Earth's motion around the Sun. ...
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Ссылки http://www.cosmos.ru/mirrors/stern/stargaze/Searlwrn.htm -- 6.9 Кб -- 22.12.2007
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1691. The Cross Staff
... It is actually a cross staff (or "Jacob's staff"), a tool widely used by astronomers and navigators before the invention of the telescope, and for a while afterwards. ... Astronomers used the cross-staff for measuring the angle between the directions of two stars. ... Since the instrument was symmetric, the angle between the directions of the stars was 2A. You can build the simple cross-staff shown on the right, using no more than a yardstick, an office ruler and simple materials found in the home. ...
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Ссылки http://www.cosmos.ru/mirrors/stern/stargaze/Scrostaf.htm -- 14.8 Кб -- 22.12.2007
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1692. Coordinates
... The system is based on two straight lines ("axes"), perpendicular to each other, each of them marked with the distances from the point where they meet ("origin")--distances to the right of the origin and above it, the origin being taken as positive and on the other sides as negative (see drawing below). ... One system (" polar coordinates ") uses the length r of the line OP from the origin to P (i. e. the distance of P distance to the origin) and the angle that line makes with the x-axis. ...
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Ссылки http://www.cosmos.ru/mirrors/stern/stargaze/Scelcoor.htm -- 13.5 Кб -- 22.12.2007
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1693. A Word of Caution
... Once upon a time , when " From Stargazers to Starships " was first written, it was just a short course at the high school level. ... All that is still there... but so are many additions! ... Sections (8), (18) and (22) expanded to 5 sections each, an entire part on the Sun was added (also covering weather, magnetism, electromagnetic waves, quantum physics and nuclear energy), and the "math refresher" grew to an entire self-contained course. ... Timeline Glossary Math index . ...
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Ссылки http://www.cosmos.ru/mirrors/stern/stargaze/Scaution.htm -- 4.5 Кб -- 22.12.2007
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1694. Article on "Stargazers"
... This article describes a new educational resource, a book-sized site on the world wide web covering astronomy, Newtonian mechanics and spaceflight. ... It could well serve as the framework of a one-year course, but it is equally suitable for individual study by any person interested in space, and it contains material for a variety of student projects, as well as a section directed at teachers. ... If astronomy and mechanics are the main courses of "Stargazers," spaceflight is the dessert. ...
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Ссылки http://www.cosmos.ru/mirrors/stern/stargaze/Sarticle.htm -- 15.6 Кб -- 22.12.2007
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1695. Applying Kepler's Third Law
... Kepler's 3rd Law . 21a.Applying 3rd Law . 21b. Fly to Mars! (1) . 21c. Fly to Mars! (2) . ... For circular orbits around Earth, we found . ... The distance of a satellite from the center of Earth in meters is an inconveniently big number, even before we raise it to the 3rd power. ... The ratio r' = (r / R E ) is the orbital distance measured in units of the Earth's radius. ... 25 638 838) = 5063.5 From this . ... This is the practical form of Kepler's 3rd law for Earth satellites. ...
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Ссылки http://www.cosmos.ru/mirrors/stern/stargaze/Sappl3rd.htm -- 9.2 Кб -- 22.12.2007
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1696. Waves and Photons--lesson plan #40
This lesson introduces students to electromagnetic waves, at a qualitative high-school level. It then brings up the concept of photons, and the relation between photon wavelength and energy. ... This lesson plan supplements: "Waves and Photons," section #S-5: on disk Sun5wave.htm , on the web . ... Qualitatively, about the concept of an electromagnetic (EM) wave, as a linked oscillation of magnetic fields and electric currents, spreading through space. ... What is a wave? ... length of one wave) . ...
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Ссылки http://www.cosmos.ru/mirrors/stern/stargaze/Lsun5wav.htm -- 26.4 Кб -- 22.12.2007
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1697. The Many Colors of Sunlight--lesson plan #39
An introduction to color and to both line spectra and continuous spectra, with applications to sunlight. ... This lesson plan supplements: "The Many Colors of Sunlight," section #S-4: on disk Sun4spec.htm , on the web . ... That cold atoms in a gas absorb the same colors as the ones they emit when hot, and that such absorbtion causes dark lines in the Sun's spectrum. ... One way of introducing the subject of color is through the rainbow. ... However, different colors are bent by different amounts. ...
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Ссылки http://www.cosmos.ru/mirrors/stern/stargaze/Lsun4spe.htm -- 24.4 Кб -- 22.12.2007
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1698. The Discovery of Atoms and Nuclei
... of Atoms and Nuclei . ... Discovery of electrons . ... The notion of atoms started from a fundamental problem in chemistry (#1): why did (say) one gram of hydrogen always combine with 8 grams of oxygen, never more, never less? ... Comparing this to Faraday's results, one could get " Avogadro's number ", the number of (say) hydrogen atoms in one gram of hydrogen--an enormously large number. ... By the way, Avogadro's number is 602,000,000,000,000,000,000,000 (6.02 10 23 ) molecules in 1 gr hydrogen. ...
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Ссылки http://www.cosmos.ru/mirrors/stern/stargaze/Ls7adisc.htm -- 12.9 Кб -- 22.12.2007
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1699. Our View of the Sun
... 24a.The Rotating Earth . ... He projected the Sun's magnified image from his telescope upon a flat white surface, and observed it there. ... The Sun's average distance from Earth, also known as the "astronomical unit" (AU), is about 150 million kilometers (93 million miles), but measuring that distance is not easy. ... Above that came the solar corona ("crown"), glowing tufts that faded into the distance, though time exposures with sensitive cameras managed to trace them to several solar radii. ...
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Ссылки http://www.cosmos.ru/mirrors/stern/stargaze/Sun2view.htm -- 19.2 Кб -- 22.12.2007
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1700. Interplanetary Magnetic Field Lines
... From the observed direction of interplanetary magnetic field lines, we believe this field comes from the Sun, carried by magnetic field lines dragged out by the solar wind . ... That is why magnetic field-line loops tend to keep back the solar wind, unlike the outward-bound lines in the "coronal holes" between them. ... The magnetic field at all these points is already so weak that the solar wind overpowers it and shifts its field lines, while its own motion--radially outward--remains unchanged. ...
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Ссылки http://www.cosmos.ru/mirrors/stern/stargaze/Simfproj.htm -- 15.6 Кб -- 22.12.2007
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