15 Weird Things That You Probably Didn’t Know About Gravity

Here on Planet Earth, we humans take gravity so for granted that it required an apple falling from a tree to produce Isaac Newton’s theory of gravitation. But gravity, which pulls objects together in proportion to their mass, is about much more than just fallen fruit. So keep reading for some of the weirdest facts about this universal force. 

1. Several areas of Hudson Bay and the nearby regions of Quebec are “missing” gravity. This is one of the parts on earth with very low gravity. – Source 

2. On Saturn’s largest moon Titan, the atmosphere is so thick and the gravity is so much low that humans could easily fly through it by flapping “wings” attached to the arms. – Source 

3. Liquid helium has almost zero viscosity and can drift through microscopic holes and up walls against gravity.–Source 

4. Einstein, about century ago, suggested in an inch long equation that “Gravity” doesn’t pull. Instead space actually pushes. “Gravity” is only the seeming effect of the curves in space. G = 8 π T. – Source

5. In zero gravity, a candle’s flame is round and blue. –Source

6. The several zero-gravity scenes in the movie Apollo 13 are essentially genuine. The crew recorded 4 hours of material in 612 parabola flights.– Source

7. The tallest likely mountains on a neutron star can only be about 5mm tall because their immense gravity.– Source

8. NASA cannot bring birds into space because birds need gravity to swallow. 

9. Humans generally get the desire to pee when the bladder is just 1/3 full. But in zero gravity, the desire doesn’t kick in until the bladder is nearly full. When astronaut John Glenn circled the Earth, his only urination was 27 ounces, seven ounces more than the capability of the regular human bladder.– Source

10. Gravity Probe B has the most perfect spheres ever made by human beings. If GP-B’s gyroscopes were inflated to the size of the Earth, the highest mountain would be only eight feet tall.– Source

11. When melting glass in space, zero gravity upsurges the viscosity and you can make glass with chemicals other than silica. – Source

12. Due to variations in local gravity, a pendulum clock precise at sea level will lose around 16 seconds per day if relocated to an altitude of 4000 feet.– Source

13. Not only do we see distant stars as they were thousands of years ago, but we also still experience their gravity from thousands of years ago, and not from where they are now. We even experience the pull of gravity from stars that have burned out. 

14. A neutron star’s gravity bends light so intensely that more than half of its exterior is visible from a given point of view. In various cases the gravity can be so great that the whole surface would be visible from certain vantage points.– Source

15. Did you know that there is an empty point in space where the gravity from the Planet Earth and the Sun is equal, and objects can orbit it as if there was something present there. – Source

outer solar system, including two gas giants; Jupiter, Saturn

Lesson 10: Completing Our Visit Close To Home

Our final lesson in this part of Astronomy 101 will concentrate primarily on the outer solar system, including two gas giants; Jupiter, Saturn and the two ice giant planets Uranus, and Neptune. There's also Pluto, which is a dwarf planet, as well as other distant small worlds that remain unexplored. 

Jupiter, the fifth planet from the Sun, is also the largest in our solar system. Its average distance is approximately 588 million kilometers, which is about five times the distance from Earth to the Sun.

It can be seen easily with the naked eye. Binoculars or a telescope may show details, like the Great Red Spot or its four largest moons. Jupiter It has no surface, though it may have a core composed of comet-like rock-forming minerals. Gravity at the top of the clouds in Jupiter's atmosphere is about 2.5 times Earth's gravity

Jupiter takes about 11.9 Earth years to make one trip around the Sun, and it's day is about 10 hours long. It is the fourth brightest object in Earth's sky, after the Sun, the Moon, and Venus.

The second-largest planet in our solar system is Saturn. It lies 1.2 billion kilometers from Earth and takes 29 years to orbit the Sun. It is also primarily a giant world of condensed gas, with a small rocky core. Saturn is perhaps best known for its rings, which are made of hundreds of thousands of ringlets of small particles.

Viewed from earth, Saturn appears as a yellowish object and can be easily viewed by the naked eye. With a telescope, the A and B rings are easily visible, and under very good conditions the D and E rings can be seen. Very strong telescopes can distinguish more rings, as well as the nine satellites of Saturn.

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Uranus is the seventh most distant planet from the Sun, with an average distance of 2.5 billion kilometers. It is often referred to as a gas giant, but its icy composition makes it more of an "ice giant". Uranus has a rocky core, completely covered with watery slush and mixed with rocky particles. It has an atmosphere of hydrogen, helium, and methane with ices mixed in.

Despite its size, Uranus's gravity is only about 1.17 times that of Earth. A Uranus day is about 17.25 Earth hours, while its year is 84 Earth years long

Uranus was the first planet to be discovered using a telescope. Under ideal conditions, it can barely be seen with the unaided eye, but should be clearly visible with binoculars or a telescope. Uranus has rings, 11 that are known. It also has 15 moons discovered to date. Ten of these were discovered when Voyager 2 passed the planet in 1986.

The last of the giant planets in our solar system is Neptune, fourth largest, and also considered more of an ice giant. Its composition is similar to Uranus, with a rocky core and huge ocean of water. With a mass 17 times that of Earth, it's volume is 72 times Earth's volume. Its atmosphere is composed primarily of hydrogen, helium, and minute amounts of methane. A day on Neptune lasts about 16 Earth hours, while its long journey around the sun makes its year nearly 165 Earth years.

Neptune is occasionally barely visible to the naked eye, and is so faint, that even with binoculars looks like a pale star. With a powerful telescope, it looks like a green disk. It has four known rings and 8 known moons. Voyager 2 also passed by Neptune in 1989, nearly ten years after it was launched. Most of what we know was learned during this pass.

The Kuiper Belt and Oort Cloud

Next, we come to the Kuiper Belt (pronounced "KIGH-per Belt"). It's a disk-shaped deep-freeze containing icy debris. It lies beyond the orbit of Neptune. 

Kuiper Belt Objects (KBOs) populate the region and are sometimes called Edgeworth Kuiper Belt objects, and sometimes are also referred to as transneptunian objects (TNOs.)

Probably the most famous KBO is Pluto the dwarf planet. It takes 248 years to orbit the Sun and lies some 5.9 billion kilometers away. Pluto can only be seen through large telescopes. Even the Hubble Space Telescope can only make out the largest features on Pluto. It's the only planet not yet visited by a spacecraft.

The New Horizons mission swept past Pluto on July 15, 2015 and returned the first-ever closeup looks at Pluto, and is now on its way to explore MU 69, another KBO. 

Far beyond the Kuiper Belt lies the Oört Cloud, a collection of icy particles that stretches out about 25 percent of the way to the next star system. The Oört Cloud (named for its discoverer, astronomer Jan Oört) supplies most of the comets in the solar system; they orbit out there until something knocks them into a headlong rush toward the Sun. 

Earth - third rock from the sun

Lesson 9: Continuing Our Visit Close To Home

We're not used to thinking of Earth as a planet, though we all know that it is. This "third rock from the sun" is also the fifth in size. The diameter of the earth at the equator is about 7926 miles, but that's not the whole story. Because the earth is not a perfect sphere but is slightly flattened at the poles, the diameter of the earth measured around the North Pole and the South Pole is about 7899 miles.

Seventy-one percent of the Earth's surface is covered with water, the only planet where it exists in its liquid form on the surface. This may account for the fact that the Earth is the only planet known to contain life.

While it's fairly easy to see portions of the Earth with the unaided eye, our close proximity prevents us from seeing it in its entirety.

One needs to travel into space for that view, and I hear it's spectacular.

The Earth has a satellite, moon, called Luna. It's 238,000 miles from the Earth and has a diameter of 2155 miles. Because of its size and rocky composition, the moon has also been called a terrestrial planet along with Mercury, Venus, Earth, and Mars. It has no atmosphere, but there is water ice in some deep craters. The moon is the only extra-planetary body that a human has visited.

Besides the sun, the moon is the brightest object in the sky and very easily seen with the naked eye. Using a telescope, you can easily map out many of the Lunar features.

The Red Planet, Mars, the seventh largest, is the fourth planet from the sun at an average distance of 141 million miles.

Mars has a very thin atmosphere made up mostly of a tiny amount of carbon dioxide (95.3%) plus nitrogen (2.7%), argon (1.6%) and traces of oxygen (0.15%) and water (0.03%).Named for the Roman god of war, Mars is about half the diameter of Earth (about 4212 miles), with one tenth Earth's mass. It's gravity is about one third that of Earth. Although Mars's surface is closest to that of Earth of any of the planets, it would still be a very harsh place to live, with temperature extremes between -225 and +60 degrees Fahrenheit, with an average of -67 degrees.

When it is in the night sky, Mars is easily visible with the naked eye. A good telescope will allow the viewer to make out details, such as the famous canals.

Mars has two moons, Phobos and Deimos. Compared to our moon, these satellites are quite small. It is believed they may have been asteroids, captured into Mars orbit. Neither satellite is visible to the unaided eye, but can be viewed with a fairly decent telescope.

Finally, this week, we'll talk a little about asteroids. The majority of asteroids fill a space between Mars and Jupiter known as the Asteroid Belt. The largest of these asteroids is 1 Ceres, at a whopping 578 miles across. The smallest are mere pebbles. The total mass of all the asteroids is less than that of the moon.

Although they are not visible to the naked eye, many asteroids can be viewed with binoculars or telescopes.

Next week, we'll finish our tour of the Solar System and our course. The end of the tunnel is in sight.

Mercury, Venus, Mars, Jupiter, and Saturn

Lesson 9: Continuing Our Visit Close To Home

Before the late 1700s, people were aware of only five other planets besides the Earth; Mercury, Venus, Mars, Jupiter, and Saturn. In 1781, Sir William Herschel, a German-born British musician and astronomer, discovered Uranus using a telescope. Citing wobbles in the orbit of Uranus, two astronomers John Couch Adams of Great Britain and Urbain Jean Joseph Leverrier of France, each independently calculated the existence and position of a new planet in 1845 and 1846, respectively.

Mercury, the second smallest planet, is the closest planet to the Sun. Its average distance is approximately 36 million miles. Mercury's diameter is 3,032 miles, and its volume and mass are about one-eighteenth that of Earth. Mercury is approximately as dense as Earth and denser than of any of the other planets.Using Leverrier's calculations, Johann Gottfried Galle of Germany first observed Neptune in 1846. The final planet, Pluto was discovered by a massive telescopic search started in 1905 by American astronomer Percival Lowell. He theorized the existence of a distant planet beyond Neptune because of slight anomalies in the orbit of Uranus. The Lowell Observatory staff, continued the search started by the man it was named for until the search ended successfully in 1930. An American astronomer, Clyde William Tombaugh, found Pluto near the position Lowell had predicted.

This lesson, we'll concentrate on the Inner Solar System, the so-called Terrestrial Planets; Mercury, Venus, Earth, and Mars as well as the asteroid belt. Next lesson, we'll look at the other planets of our solar system.

Mercury's orbit takes it around the Sun approximately every 88 Earth days. One Mercury day, the time it takes to revolve around its axis, is equal to just under 59 Earth days. Mercury can be viewed with binoculars or even the naked eye, but it is always close to the Sun and hard to see in the twilight sky.Its gravity on the surface is about one-third of the Earth's and about twice that of the Moon.

Venus, the sixth largest planet, is the second in distance from the sun. It's average distance from the sun is around 67 million miles. It has a diameter of around 7,500 miles. Conditions on the surface of Venus are fairly stable, but would be very unpleasant for humans. The temperature is about 864° F and the surface pressure is 96 bars (Compare that to 1 bar for Earth). Venus's atmosphere is nearly all carbon dioxide (CO2). It has a cloud base at about 31 miles, made mostly of sulfuric acid.

Besides the sun and the moon, Venus is the brightest object in the sky. It is known as the morning star when it appears in the east at sunrise, and the evening star when it is in the west at sunset. It is easily visible with the unaided eye, and when viewed through a telescope, exhibits phases like the moon.

We're not used to thinking of Earth as a planet, though we all know that it is. This "third rock from the sun" is also the fifth in size. The diameter of the earth at the equator is about 7926 miles, but that's not the whole story. Because the earth is not a perfect sphere but is slightly flattened at the poles, the diameter of the earth measured around the North Pole and the South Pole is about 7899 miles.

One needs to travel into space for that view, and I hear it's spectacular.Seventy-one percent of the Earth's surface is covered with water, the only planet where it exists in its liquid form on the surface. This may account for the fact that the Earth is the only planet known to contain life.

While it's fairly easy to see portions of the Earth with the unaided eye, our close proximity prevents us from seeing it in its entirety.

The Earth has a satellite, moon, called Luna. It's 238,000 miles from the Earth and has a diameter of 2155 miles. Because of its size and rocky composition, the moon has also been called a terrestrial planet along with Mercury, Venus, Earth, and Mars. It has no atmosphere, but there is water ice in some deep craters. The moon is the only extra-planetary body that a human has visited.

Besides the sun, the moon is the brightest object in the sky and very easily seen with the naked eye. Using a telescope, you can easily map out many of the Lunar features.

The Red Planet, Mars, the seventh largest, is the fourth planet from the sun at an average distance of 141 million miles.

Mars has a very thin atmosphere made up mostly of a tiny amount of carbon dioxide (95.3%) plus nitrogen (2.7%), argon (1.6%) and traces of oxygen (0.15%) and water (0.03%).Named for the Roman god of war, Mars is about half the diameter of Earth (about 4212 miles), with one tenth Earth's mass. It's gravity is about one third that of Earth. Although Mars's surface is closest to that of Earth of any of the planets, it would still be a very harsh place to live, with temperature extremes between -225 and +60 degrees Fahrenheit, with an average of -67 degrees.

When it is in the night sky, Mars is easily visible with the naked eye. A good telescope will allow the viewer to make out details, such as the famous canals.

Mars has two moons, Phobos and Deimos. Compared to our moon, these satellites are quite small. It is believed they may have been asteroids, captured into Mars orbit. Neither satellite is visible to the unaided eye, but can be viewed with a fairly decent telescope.

Finally, this week, we'll talk a little about asteroids. The majority of asteroids fill a space between Mars and Jupiter known as the Asteroid Belt. The largest of these asteroids is 1 Ceres, at a whopping 578 miles across. The smallest are mere pebbles. The total mass of all the asteroids is less than that of the moon.

Although they are not visible to the naked eye, many asteroids can be viewed with binoculars or telescopes.

Next week, we'll finish our tour of the Solar System and our course. The end of the tunnel is in sight.

What is a solar system

Lesson 8: Visiting Close to Home 

What is a solar system?

It consists of a star, orbited by planets or smaller rocky bodies. The gravitational pull of the star holds the system together. Our solar system consists of our sun, which is a star called Sol, nine planets including the one we live on, Earth, along with the satellites of those planets, a number of asteroids, comets, and other smaller objects. For this lesson, we'll concentrate on our star, the Sun.

Sun:

While some stars in our galaxy are nearly as old as the universe, about 15 billion years, our sun is a second-generation star. It is only 4.6 billion years old. Some of its material came from former stars.

Stars are designated by a letter and a number combination roughly according to their surface temperature.

The classes from hottest to coolest are: W, O, B, A, F, G, K, M, R, N, and S. The number is a subcategory of each designation. Our Sun is designated as a G2 star. Astronomers describe Sol as a very ordinary star. It acts just as would be expected from a star of similar size.

Star masses typically range from 0.3 to 3.0 times the mass of the Sun with most stars having masses similar to that of the Sun.

Our solar system is part of a larger system known as a galaxy. The name of our galaxy is the Milky Way. The Milky Way contains about 100 million stars, all revolving around a point known as the galactic center. We are located in the outer part of the galaxy, approximately 1.6 × 1017 miles from the Galactic center.

At our current orbital speed of 140 miles/second, our solar system takes about 250 million years for one orbit around the Galactic center.

Since its creation, our star has used up about half of the hydrogen in its core. Over the next 5 billion years or so, it will grow steadily brighter as more helium accumulates in its core.

As the supply of hydrogen dwindles, the Sun's core must keep producing enough pressure to keep the Sun from collapsing in on itself. The only way it can do this is to increase its temperature. Eventually it will run out of hydrogen fuel. At that point, it will go through a radical change which will most likely result in the complete destruction of the planet Earth.

The sun should never be viewed directly, either with or without a magnifying device. Permanent damage can be caused in a fraction of a second unless proper precautions are taken. There are filters which can be utilized with many telescopes. (SUNGLASSES ARE NOT ADEQUATE!) Consult someone with a lot of experience before attempting Solar viewing.

Sun Statistics:

• diameter: 1,390,000 km.
• mass: 1.989e30 kg
• temperature: 5800 K (surface) 15,600,000 K (core)

A very interesting phenomenon associated with the Sun is called an eclipse. It happens when our own moon passes between the Earth and the Sun, blocking out all or part of the sun from view. Even though a portion of the sun is blocked, it is even more dangerous to view the sun during an eclipse than during a normal day.

In our next lesson, we'll take a closer look at the Inner Solar System.

patterns in the sky- connect the dots

Lesson 7: Star Power: Playing Connect the Dots With Stars

What do you do with your free time when movies, television, and even radio haven’t been invented, and won’t be for hundreds, or even thousands of years? That's the issue our ancient ancestors faced. They told stories, performed plays, wrote poetry — and, at night — looked to the sky and the stars, wondering about what they saw.

These simple activities WERE the birth of astronomy. It was a simple beginning; people noticed the stars in the sky.

Then, they named the stars. The science of astronomy grew slowly, as scientists figured out what the different objects in the sky are and learned more about them by studying them through telescopes and other instruments.

The Birth of the Constellations

Besides stargazing, the ancients noticed that the stars appeared in patterns in the sky.

So, they played cosmic "connect the dots" with the stars to create patterns that looked like animals, gods, goddesses, and heroes. Then, they created stories about these patterns of stars, which are called constellations — or constellation outlines.

The constellation patterns and their stories date back thousands of years to many cultures. For example, the constellationsUrsa Major and Ursa Minor, the Big Bear and the Little Bear, have been used by different populations around the world to identify those stars since the Ice Ages.

Most names, however, come from ancient Greece and those are what we use. However, many other cultures throughout the world created their own patterns and stories for the stars, based on their own legends and beliefs.

Exploring a Star Pattern That's NOT a Constellation

In Lesson 6, you located the Big Dipper as a "landmark" in the sky. Although most people can recognize the Big Dipper, those seven stars are not really a constellation. They form what is what is known as an "asterism", or a group of stars. The Big Dipper is actually part of Ursa Major.

Likewise, the Little Dipper is a part of Ursa Minor. On the other hand, our "landmark" for the south, the Southern Cross is an actual constellation called Crux.Its long bar seems to point toward the actual region of the sky where Earth's south pole points (also called the South Celestial Pole).

There are 88 official constellations in the Northern and Southern Hemispheres of our sky. Depending on where you live, you will probably see more than half of them throughout the year. Study the stars in each constellation, and then as you get more familiar with them, start to look for other objects hidden among the stars. 

To figure out which constellations you're looking at in the night sky, you can use star charts (such as those found online at Sky&Telescope.com or Astronomy.com. Or, you can use planetarium software such as Stellarium (Stellarium.org), or an astronomy app on your portable device. There are many apps and programs that will help you make useful star charts for your observing enjoyment.

Next lesson, we'll take a look closer to home and study our own solar system.

sky observation - need not to buy Telescope

Lesson 6: Starry Eyed; Getting Started Star Gazing With a Sky Map

OK, we know a little more about stars now. They’re just big balls of fiery gas. This lesson, Let’s spend a little time looking at them. Stargazing is many people's favorite part of astronomy.

However, a few words of advice about how to explore the sky are in order.

First, don’t rush off to the store to buy a telescope just yet. For most sky observing, you don’t need much equipment at all. You DO need some information and, perhaps, a red flashlight.

Star Charts

Just like when we travel, we need a road map, when we search the skies, we need a sky map to lead us to the stars. There are many very good maps for sale at hobby shops that specialize in astronomy, or inbooks about astronomy. you can make them using astronomy software or apps, or use the ones printed in astronomy magazines such as Astronomy (Astronomy.com) andSky & Telescope (SkyandTelescope.com)

Your Viewing Area

In order to have the best views of the sky, you should try to find a nice size field, preferably with as little light around as possible to minimize interference from light pollution. Light tific Evidence Causes Scientists to Speak About God

pollution is any light around you which prevents your eyes from adjusting to the dark, thereby making star gazing more difficult. Your back yard may work just fine.

Now, lie on your back. It doesn’t matter which direction your head is pointed as long as you know how you’re oriented and orient your sky map accordingly.  For this lesson, we'll concentrate on things that can be seen from mostly from Northern Hemisphere locations.

Next, just like when we travel, we need to find a “landmark” we can recognize.

Great! Now, if you think of the two stars which from the wall of the dipper connected its handle as a pointer, they aim directly at Polaris, the North Star, which in turn starts the handle of the little dipper. See, now you’re star gazing.Since most people can find the Big Dipper, let’s look for it first.

Orient the sky map with the N pointed towards north. Now, locate the Big Dipper and Little Dipper on the map and you’re ready to set off on your exploration. If you can get a red flashlight, or place some red cellophane over the lens of a standard flashlight, when you shine it on the map, your night vision won't be as affected as with a white light.

These instructions work fine for the northern hemisphere. If you are located south of the equator, it's possible you'll want a different landmark. Probably the most easily recognizable constellation which can be seen from the southern hemisphere is the Southern Cross. Once you locate this constellation, use it to orient yourself on the sky map.

Don't expect to see everything at once, it's a very large universe. When you've had a little experience with star gazing, you can consider buying a telescope. Talk to someone with more experience about the best telescope to buy.

Don't worry too much about identifying the objects you are viewing, just enjoy the splendor of the night sky. If curiosity does get the better of you, simply glance at your map and you should be able to recognize many of the stars and/or planets that are visible. Remember that the Earth is constantly moving, so allow for that movement as you look at the map.

Here is a listing of the 10 brightest stars. Remember that not all of these stars will be visible from where you are or at the time you are looking.

Next lesson, we’ll talk more about the stars and constellations you’re viewing.

Assignment

Spend a few nights viewing the sky. Learn to quickly recognize the Big Dipper, Little Dipper, and Polaris or The Southern Cross. Check out this list of the top 10 brightest stars. Don't forget the discussion Forum.

Stars - Those stars you see with your naked eye in the night sky all belong to the Milky Way Galaxy

Stars are massive shining spheres of hot gas. Those stars you see with your naked eye in the night sky all belong to the Milky Way Galaxy, the huge system of stars that contains our solar system. There are around 5,000 stars which can be seen with the naked eye, though not all stars are visible at all times and places. With a smalltelescope, hundreds of thousands of stars can be seen.

Larger telescopes can show millions of galaxies, which can have upwards of a trillion or more stars.

There are more than 1 x 1022 stars in the universe (10,000,000,000,000,000,000,000). Many are so large that if they took our Sun's place, they would engulf Earth, Mars, Jupiter, and Saturn. Others, called white dwarf stars, are around the size of Earth, and neutron stars are less than about 16 kilometers (10 miles) in diameter.

Our Sun is about 93 million miles from Earth, 1 astronomical Unit (AU). The difference in its appearance from the stars visible in the night sky is due to its close proximity. The next closest star is Proxima Centauri, 4.2 light-years (40.1 trillion kilometers (20 trillion miles) from Earth.

Stars come in a wide variety of colors, ranging from deep red, through orange and yellow to an intense white-blue. The color of a star depends on its temperature. Cooler stars tend to be red, while the hottest ones are blue.

Stars are classified many ways, including by their brightness. They are also divided into brightness groups, which are called magnitudes. Each star magnitude is 2.5 times brighter than the next lower star.

The brightest stars now represented by negative numbers and they can be dimmer than 31st magnitude. 

Stars - Stars - Stars

Stars are primarily made of hydrogen, smaller amounts of helium, and trace amounts of other elements. Even the most abundant of the other elements present in stars (oxygen, carbon, neon, and nitrogen) are only present in very small quantities.

Despite the frequent use of phrases like "the emptiness of space," space is actually full of gases and dust. This material gets compressed by collisions and blast waves from exploding stars, causing lumps of matter to form. If the gravity of these protostellar objects is strong enough, they can pull in other matter for fuels. As they continue to compress, their internal temperatures rise to the point where hydrogen ignites in thermonuclear fusion. While the gravity continues pulling, trying to collapse the star into the smallest possible size, the fusion stabilizes it, preventing further contraction. Thus, a great struggle ensues for the life of the star, as each force continues to push or pull.

How Do Stars Produce Light, Heat, and Energy?

There are a number of different processes (thermonuclear fusion) which make stars produce light, heat and energy. The most common happens when four hydrogen atoms combine into a helium atom. This releases energy, which is converted to light and heat.

Eventually, most of the fuel, hydrogen, is exhausted. As the fuel begins to run out, the strength of the thermonuclear fusion reaction declines. Soon (relatively speaking), gravity will win and the star will collapse under its own weight. At that time, it becomes what is known as a white dwarf. As the fuel further depletes and reaction stops all together, it will collapse further, into a black dwarf. This process can take billions and billions of years to complete.

Toward the end of the twentieth century, astronomers began to discover planets orbiting other stars. Because planets are so much smaller and fainter than stars, they are difficult to detect and impossible to see, so how do scientists find them? They measure tiny wobbles in a star’s motion caused by the gravitational pull of the planets. Although no Earth-like planets have been discovered yet, scientists are hopeful. Next lesson, we'll take a closer look at some of these balls of gas.

Man Behind the Comet - Edmund Halley

Meet the Man Behind the Comet

Edmund Halley is famous the world over for the work he did to identify Comet Halley from orbital measurements. For his labors, his is name attached to this famous comet.  Who was he?

Edmund Halley's official birth date is November 8, 1656. At the age of 17, he entered Queen's College Oxford, already an expert astronomer. He carried with him a wonderful collection of astronomical instruments purchased for him by his father.

Halley Makes a Name for HimselfHe worked for John Flamsteed, the Astronomer Royal and was so useful that when Flamsteed published his findings inPhilosophical Transactions of the Royal Society in 1675, he mentioned his protegé by name. On August 21, 1676 Halley observed an occultation of Mars by the Moon, and published his findings.

Halley put his Oxford career on hold to go map the southern skies. He cataloged 341 southern stars and discovered a star cluster in the constellation Centaurus. He also made the first complete observation of a transit of Mercury across the face of the Sun. 

Halley returned to England in 1678 and published his catalogue of southern hemisphere stars. King Charles II decreed that the University of Oxford confer a degree on Halley, without his having to take exams. He was also elected a member of the Royal Society at 22, one of its youngest members. All these honors did not sit well with John Flamsteed. Despite his earlier liking of Halley, Flamsteed came to consider him an enemy.

During his travels, Halley observed a comet. He worked with Giovanni Cassini to determine its orbit.  tha the inverse square law of attraction. He discussed Kepler's third law as a possible way of understanding that orbit with his colleagues Christopher Wren and Robert Hooke.Travels and Observations

He visited Isaac Newton and urged him to publish his Principia Mathematica, which discussed the same issues of planetary orbits.

In 1691, Halley applied for the Savilian Chair of Astronomy at Oxford, but Flamsteed blocked the appointment. So, Halley edited Philosophical Transactions, published the first actuarial tables, and made careful studies of comets. In 1695, when Newton accepted the position of Master of the Mint, he appointed Halley deputy controller of the mint at Chester.

Heading out to Sea and Into Academia

Halley accepted command of the ship Paramour, on a scientific expedition. He studied the variation between magnetic north and true north, and published a map showing isolines, or points of equal value of deviation.

In 1704, he was finally appointed Savilian Professor of Geometry at Oxford, which upset Flamsteed. When Flamsteed died, Halley succeeded him as Astronomer Royal. Flamsteed’s widow was so angry she had her late husband’s instruments sold so Halley could not use them.

Discovering Comet Halley

Halley turned his attention to work he had started in 1682. Armed with Kepler’s Laws of Planetary Motion, and Newton’s theories of elliptical orbits, Halley recognized that the comets of 1456, 1531, 1607, and 1682 all followed similar paths. He then that these were all the same comet. After publishing his theory, Synopsis on Cometary Astronomy in 1705, it was simply a matter of waiting for the next return to prove his theory.

Edmund Halley died January 14, 1742 in Greenwich, England. He did not survive to see the return of his comet on Christmas day in 1758.

Father of modern astronomy-Tycho Brahe

Tycho Brahe has often been called the Father of modern astronomy, and for good reasons. However, I think that title really belongs to Galileo Galilei for his pioneering use of the telescope to magnify the view of the sky. However, Brahe did advance the science more than anyone in the past, simply by using his senses, rather than philosophy to study the sky.

The work that Brahe began was continued and expanded by his assistant, Johannes Kepler, whose laws of planetary motion are among the foundations of modern astronomy.

Sir William Herschel (1738-1822), though born in Germany, was a British astronomer. He discovered Uranus in 1781 coined the word "asteroids". He also cataloged about 2,000 nebulae, discovered several satellites of Uranus and Saturn, studied the rotation of planets. Discovered and studied binary stars. He discovered two satellites each orbiting Uranus and Saturn. He studied the rotation period of many planets, the motion of double stars, and nebulae. He cataloged more than 800 double stars and contributed new information on the constitution of nebulae. Herschel was the first to propose that these nebulae were composed of stars. He is considered the founder of sidereal astronomy.There are many other astronomers since Galileo, Brahe, and Kepler who have advanced the science:  Here, in brief, are some of the other bright lights who helped bring astronomy to its current place.

• Edmund Halley (1656-1742) was a British astronomer who was also a big fan of Sir Isaac Newton. After encouraging Newton to write his Principia, Halley then published it at his own expense. Not stopping to rest on the fame of another, he went on to calculate the orbits of comets, including the one named after him.

• Albert Einstein (1879-1955) was a German-born American physicist and Nobel laureate. He may be the most well-known scientist of the 20th century. In 1915, he developed his general theory of relativity, which states that the speed of light is constant and that the curvature of space and the passage of time are linked to gravity. Thinking the universe was unchanging, he inserted a  cosmological constant "fudge factor" into his calculations to make them fit his viewpoint.

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  Edwin P Hubble (1889-1953), American Astronomer. In the 1920s, Albert Einstein stated, "I have made my greatest blunder." This pronouncement came when Hubble demonstrated that the universe was not static and Einstein's cosmological constant was not necessary. Utilizing improved telescopic devices, he was also able to confirm that those "fuzzy" objects astronomers had seen for years were in fact other galaxies.Willem de Sitter: (1872 - 1934), a Dutch astronomer, removed Einstein's cosmological constant from his calculations and used the theory of relativity to show that the universe may always be expanding.
• Georges-Henri Lemaitre: (1894 - 1966) was not only a Belgian astronomer, he was also a Jesuit priest. Discovering the writings of Russian mathematician, Alexander Friedmann, Lemaitre took his solution for an expanding universe and theorized that if the universe is expanding, if we follow it back to the starting point, then our universe began as a great "cosmic egg" which exploded and expanded outward. Lemaitre is often referred to as the father of the Big Bang theory.

• Thomas Gold (1920 - 2004) was an American astronomer. Though it is generally believed that Gold's "steady state" theory of the universe is incorrect, he made many major contributions to our knowledge of the universe, including the nature of pulsars as rotating neutron stars, and the origin of planetary hydrocarbons.

These are just a few of the astronomers and their findings in the pre- and early 20th century history of astronomy. There have been and are many other great brains in the field of astronomy, but it's time to get away from history for now. We'll meet some of these other astronomers throughout the rest of our lessons. Next, we'll look at numbers.