With the anticipation of the upcoming solar eclipse why don't we have a look at stargazing? I used to be a stargazer in my early teens. More has been added to this.
I didn't do really a lot of stargazing but did see four of the moons of Jupiter and the rings of Saturn. I saw Uranus, which cannot be seen with the unaided eye. Venus actually goes through phases like the moon, it can't be seen with the unaided eye but can be seen with a telescope.
The stars are still there during the day but are drowned out by the light of the sun. On the moon the sun and stars can be seen at the same time but there is dust particles in earth's atmosphere that scatters sunlight all around, causing the sky to appear blue. Electromagnetic radiation is reflected by objects that are about the same size as the wavelength of the radiation and the microscopic dust particles reflect blue light, this is why the sky appears blue. At evening or morning the sun shines through a greater thickness of atmosphere so that the blue light is scattered out into space altogether. This is why sunrise and sunset appears as red and orange. During a forest fire the sky sometimes appears as yellow or orange because there are temporarily larger dust particles in the air that scatter longer wavelengths of light.
The atmosphere doesn't actually end at a given altitude, it gradually fades out. Where the atmosphere ends and space begins is a matter of definition. There is a line called the Karmann Line, beyond which the velocity necessary to keep an aircraft with wings flying would be greater than the velocity needed to put it into orbit. But that is a definition from a technology point of view. Most people would probably say that space is where satellites can orbit safely, without their orbits being hindered by friction with traces of atmosphere.
The two brightest objects, other than the sun, and moon are Venus and Jupiter, Venus is a little bit brighter. The way to tell them apart is that Venus is closer to the sun than earth and so can only be seen after sunset or before sunrise. Unlike Jupiter, Venus is never seen in the middle of the night.
The stars are arranged into groups called "constellations", or imaginary pictures. The constellations were first defined in ancient times. Some constellations are seen more clearly than others. I thought that the easiest to see constellations are the Big Dipper and Cassiopeia, near the north celestial pole, Scorpio and Taurus, in the northern hemisphere summer, Orion and Gemini, in the northern hemisphere winter.
The two stars on the outside of the bowl of the Big Dipper point to the North Star. It is not a particularly bright star but this makes it easy to find. The North Star has been used since ancient times because, as the name implies, the star is at the north celestial pole and when you face it you are facing north. South would be behind you, west on your left, and east on your right. On other planets the stars would be the same but the rotational axes of the planets are not aligned so each planet would have a different North Star.
If I happen to be in a rural area at night I still try to take the opportunity to look at the sky. There are multitudes of stars that cannot be seen in the city. Using even simple equipment such as a pair of binoculars reveals thousands more stars than can be seen with the eyes alone.
I used to measure the passage of summer by the two bright summer stars, Arcturus and Vega. When Arcturus appears overhead in the early evening we know that summer is here. As the summer wears on, Arcturus gets lower in the western sky and Vega appears overhead in the early evening. But when Vega gets lower in the western sky I knew that the end of summer was getting near and it was almost time to go back to school. In the same way, if I was up late at night and happened to see Orion, I would know that winter was on the way.
On a clear night in a rural area the Milky Way can often be seen. This is the dense band of faint stars across the sky. We live in what is known as a barred spiral galaxy. When we look at the Milky Way we are looking along the plane of the galaxy.
The planets of our Solar System orbit the sun in roughly the same geometric plane as each other. Our galaxy, commonly referred to as the Milky Way, is a barred spiral galaxy that is also aligned along one plane. But the two planes are not at all the same. There is a difference of about 60 degrees, one sixth of a complete circle, between them. The center of the galaxy is in the direction of the southern stars of the northern hemisphere summer. Our location is far out on one of the arms of our spiral galaxy.
The moon is obviously by far the easiest object to observe. The orbit of the moon around the earth is in almost the same geometric plane as the orbit of the earth around the sun, but there is a difference of about 5 degrees between them. If the two orbits were in exactly the same plane there would be both a lunar and a solar eclipse every month. A solar eclipse is when the new moon casts it's shadow on the earth. A lunar eclipse is when the earth casts it's shadow on the full moon. The diameter of the sun is about 400 times that of the moon but it is also about 400 times as far away, so that the sun and moon appear as about the same size in the sky.
The moon is tidally locked to the earth so that the same side of the moon always faces earth. The dark "seas" that can easily be seen on the moon are actually lava plains from the moon's distant past. The moon orbits earth every 29 days in the same direction as the earth rotates, which is eastward. If we divide 24 hours by 29 it means that the moon rises 50 minutes later each day.
Because the planets all orbit the sun in close to the same geometric plane they seem to follow a path as they move across the sky. This path is known as the Ecliptic. There is what is known as the "Celestial Equator", which is a reflection of earth's equator in space. But since the earth is tilted on it's axis by 23 1/2 degrees as it moves around the sun, which is what gives us the seasons, the Celestial Equator forms a sine wave across the sky, through the course of the year, rather than a straight line.
Planets were originally distinguished from stars because planets gradually move relative to the fixed background stars. The word "planet" actually means "wanderer". The twelve constellations along the ecliptic, which forms the background to the movement of the planets, is known as the Zodiac. So it might be said, for example, that "Mars is in Gemini".
Another way that planets are distinguished from stars is that stars seem to "twinkle" while planets shine with a steady light. I believe that this twinkling is caused by the polarity of light. Light may or may not be polarized, which means all the waves aligned in the same geometric plane. Our eyes ordinarily cannot tell whether light is polarized or not. The twinkling of stars is caused by the continuous and random changes in the polarity of the light. When light is reflected from a surface it is partially polarized. This is why planets do not display the same twinkling.
Uranus and Neptune are not visible to the unaided eye. Mercury is difficult to see because it is close to the sun and thus only seen just after sunset or just before sunrise. This is for the same reason that Venus is only seen after sunset or before sunrise, it is closer to the sun than the earth. But Mercury is even closer to the sun than Venus, which makes it difficult to see.
The planets revolve around the sun but at different speeds, according to their distances from the sun. A planet is best seen from earth when it is directly opposite the earth, said to be in opposition. The orbits of the planets are not circles but ellipses, meaning that planets at opposition are not always the same distance apart, and obviously a planet is at it's brightest and best-seen when it is closest to earth.
Venus is closer to the sun than earth so it moves through it's orbit faster than earth. At dawn the direction that the earth is moving through it's orbit around the sun is directly overhead. Venus, because it is closer to the sun, can only be seen either just after sunset or just before sunrise. When Venus is catching up to earth in it's orbit it appears after sunset, in the west. When Venus passes the earth in it's orbit it then appears before sunrise, in the east.
Some of what can be seen in the night sky are nebula, distant clouds of gas and dust. A few of what appear to be nebula are actually other galaxies. I have seen the Andromeda Galaxy, it is visible with the eyes alone if you know where to look, appearing like a patch of light. The Andromeda Galaxy is similar in form to our galaxy but it is larger. It is the largest galaxy in our Local Group of galaxies, ours is the second-largest. In the southern hemisphere the Magellanic Clouds are two satellite galaxies of our galaxy that are prominently visible.
The night sky has been especially important in the Middle East since ancient times. The Pyramids of Giza are almost universally considered to be arranged like the stars in the belt of Orion, as we saw in "The Underground Orion Correlation Theory" March 2016. The brightest stars were named in ancient times but about two hundred other stars have Arabic names. This is a legacy of the Golden Age of Islam, when learning was centered around the "House of Wisdom" in Baghdad.
Arabs, along with Chinese and Japanese sources, documented the supernova that resulted in what we see today as the Crab Nebula, in the year 1054, while there is little evidence that Europeans paid any attention to it.
Astronomy today is often concentrated in the southern hemisphere, particularly Chile, simply because most of the world's people live in the northern hemisphere so that the northern stars have been much more studied. The ideal place for a telescope is on a mountain in the desert, because it will be above much of the atmosphere and there will be less water in the air and less likelihood of cloud cover. Another important place for astronomical observations is the high mountain tops of the large island of Hawaii.
The Mount Wilson Observatory, above Los Angeles, that we saw in "Travel Photos Of North America", used to be very important in astronomy, until it's viewing was increasingly drowned out by the bright light of Los Angeles. This is where it was discovered that the universe is expanding.
The closer to the equator the observer is the more total stars can be seen over the course of the year. From a vantage point on the equator, with a clear view and a flat horizon, an observer can theoretically see every star that is visible from earth, over the course of the year. But from either the north or south pole only half of the stars will ever be visible because the stars of the opposite hemisphere will always be below the horizon. When I traveled across the southern U.S. I noticed stars that I had never seen before.
A different set of stars is seen for each season, because the earth faces different directions in space as it goes through it's orbit around the sun. My favorite stars were the winter ones even though I would, of course, rather be outside during the summer.
The stars change by season, as the earth goes through it's orbit around the sun. But at every latitude except right on the equator some stars, the ones near the north or south celestial equator, are visible throughout the year. These are known as the "circumpolar constellations". From any latitude that many degrees from the nearest celestial pole will be circumpolar constellations. I live at 43 degrees north so I can always see the Big Dipper and Cassiopeia, at any time of the year. From the north or south pole all visible constellations are theoretically circumpolar constellations, while there are theoretically no circumpolar constellations from the equator.
The brightness of a star is expressed as magnitude, the lower the number the brighter the star. A star's apparent brightness depends both on it's actual magnitude and it's distance from us. Many of the stars that we see are much larger and brighter than the sun, which is an average star if we exclude the numerous red dwarfs. The brightest star in the sky is Sirius, which is about twice as big as the sun but relatively close by.
The distances to stars are measured in light-years, which is the distance that light travels in a year, about 10 trillion km. The distances to nearer stars can be measured by parallax against more distant stars by measurements taken six months apart when the earth is on opposite sides of it's orbit around the sun. But this method is only accurate to about 50 light years and distances to further stars must be estimated by more indirect methods.
Distances are sometimes expressed in parsecs, or parallax-seconds, with a "second" meaning 1 / 60 of 1 / 60 of a degree of parallax as described above. A parsec is equal to 3.26 light-years because this is how far away a star would be that had a parallax difference of one second of arc when observed from opposite sides of the earth's orbit. This is similar in concept to a nautical mile, which is one minute of arc, or 1 / 60 of a degree, of the earth's circumference. A nautical mile is equal to 1.15 statue miles. Much lesser distances may be expressed in Astronomical Units, AU, which is the average distance between the earth and the sun.
ASTRONOMICAL EQUIPMENT
There are two basic types of optical telescope, a reflecting telescope that uses a concave mirror to gather light and focus the image and a refracting telescope which uses a lens. All of the world's largest telescopes use mirrors simply because a mirror can be supported from beneath, while a lens can't, so that concave mirrors can be made much larger than lenses. A lens can be supported only by it's edges, without blocking the image, and a lens that is too heavy will sag under it's own weight.
But for small portable telescopes many people think refracting telescopes, using a lens, is better because reflecting telescopes, using mirrors, must have a small secondary mirror, to reflect the image to the eyepiece, and the whole arrangement can be knocked out of alignment.
These are two refracting telescopes that I had. There was a tripod for the larger one. I never had a reflecting telescope.
The difference between a telescope intended for terrestrial use, including binoculars, and one intended for astronomical use is that the astronomical telescope delivers the image upside-down. The reason is that the terrestrial telescope contains a third lens, aside from the objective lens and the eyepiece, to turn the image right side up. But the surface of this extra lens inevitably reflects away some of the precious light that the telescope has gathered. So the third lens is done away with in astronomical telescopes because it really doesn't matter if the image is upside-down. The objective is to gather as much light as possible.
A telescope operates like a lever. With a lever we can trade distance for force. With a telescope we can bring distant objects much closer, at the expense of field of view. A telescope that is based on a lens has a large objective lens that is pointed at the object and a small eyepiece lens that the observer looks through. Every lens has a focal length, usually the larger the lens the longer the focal length. The magnification of the telescope is the ratio of the focal length of the objective lens divided by that of the eyepiece, the same way that a lever works.
Aside from looking at the moon what is really important in looking at space is not how much magnification power the telescope has, even in the most powerful telescopes stars still appear as points of light, but how much light it can gather, which depends primarily on the size of the objective lens or mirror. This will enable stars and objects to be seen that wouldn't be visible otherwise. When a telescope is referred to in terms of inches, centimeters or, meters it is referring to the diameter of the objective lens or mirror.
Astronomy has always been a science with a heavy amateur participation and many discoveries have been made by amateurs. There are astronomical telescopes today that work with, and are directed by, smartphones that can use artificial intelligence to cancel out the city lights all around. But your worst enemy will still be clouds.
Amateur astronomy is so important because professional astronomers, each working on a specific task, cannot possibly watch everything that goes on in the sky. But a network of people across the world with their own telescopes can. A major difference between amateurs and professional astronomers is that amateurs deal almost exclusively with visible light while professionals deal with information from the entire electromagnetic spectrum. Professional astronomy is also more math-intensive. An amateur astronomer might discover a comet while professionals would calculate it's orbit.
Aiming a telescope at an object that you can see with your eye alone is easy enough but finding an object that you can't see with your eyes alone is more difficult. There is a system of stellar coordinates, or you can use bright stars as reference points and find the target object from there. The large telescope in the photo offered from 20x to 60x magnification. When looking for an object that I couldn't see with my eyes alone, such as Saturn, I would start with low magnification, which gives a wider field of view, then zoom in when I found it.
You cannot turn a light on while stargazing or it will ruin your night vision. I had a star chart that glowed in the dark. The stars have been divided into constellations, or imaginary pictures, since ancient times. The stars move as the earth turns so to take astronomical photos, which usually requires extended exposure, it is necessary to have a motor that drives the telescope to match the movement of the stars.
Satellites can be seen going over but only during a limited window of time. To see a satellite it must be dark where you are but the sun must still be shining on the satellite. A satellite cannot be seen in the middle of the night because the light of the sun is blocked by the earth. Unless you live relatively near the equator only satellites in polar orbits, moving north-south, can usually be seen. As more and more satellites are launched it is bringing conflict with the astronomical community, which claims the satellites ruin photographic images by showing up as streaks of light.
In my youth I watched Skylab going over, as it's orbit decayed before it burned up in the atmosphere. Pieces of it were found in Australia. It appeared as a moving bright light in the evening because it was dark where I was but the sun was still shining on it.
You can actually use the sunset to measure the altitude of a high object. After the sun sets it will get dark where you are but the sun will still be shining on the object. But as the earth continues turning the object will go dark when it gets into the shadow of the earth, or if it turns orange because it is now receiving only light refracted by the atmosphere. If you can get the exact time that the object ceased being exposed to direct light and the exact time the sun set, you can calculate how far the earth turned to get the sunlight on the object to change. Considering the earth's diameter and circumstance you can then draw a diagram that will show the altitude of the object. Remember to multiply the equatorial circumstance of the earth by the cosine of your latitude. Clouds appear white in direct sunlight, orange in refracted sunlight and purple when there is only scattered light. If there are low cumulus and high cirrus clouds at the same time sometimes you can see, after sunset, the cumulus will be orange while the cirrus is still white.
"Shooting Stars", which can usually be seen on any clear night, are observed with the eyes alone, since their appearance is unpredictable. A "shooting star" is really a meteor, an object moving at high speed through space that burns up by friction with the atmosphere. Most of the "shooting stars" that you see are no larger than a grain of sand. Large meteors can make it to the earth's surface without burning up, they are then known as meteorites. All metal deposits that we mine came from meteorites, which is why their locations are so unpredictable.
In the early morning of August 25, 1995, between North Tonawanda and Niagara Falls, my car had overheated and I was waiting for it to cool so I could drive some more. I happened to see a brilliant blue light crossing the sky from northeast to southwest. I wasn't sure of the scale of it but there were a few cumulus clouds and I could see that it illuminated the clouds from above. It looked like a blazing blue comet. My first thought is that it was a plane and horror that I had witnessed the death of a plane full of people. I went all around the radio dial (before phones were common) but there was nothing about a plane crash. The news the next day had nothing about a plane crash. Then I read that it was a meteor and hundreds of people had seen it.
I saw the northern lights once, incidentally from the top level of a parking ramp. It looked like a glowing green curtain.
I saw comet Hale-Bopp, in 1997, but it is difficult to tell in advance what a visual impact a comet will make and some, like Kohoutek in my early teens, were not easy to see. Comets have tails when they get near the sun because they are at least partially made of ices and the sun vaporizes some of it on each orbit. The tail of a comet thus always points away from the sun. The water on earth almost certainly came from comets.
Much of the future of astronomy should be in telescopes that are based in space. The Hubble Space Telescope has been a fantastic success that has far exceeded all expectations. It is in orbit around the earth. The newer James Webb Telescope is actually in orbit around the sun, but at a Lagrangian Point so that it stays in the same position relative to earth. But large earth-based telescopes are still being built. Radio telescopes require large antenna so it is not practical to put one in space, although the wavelengths of radio waves that are reflected by the ionosphere naturally cannot be received on earth.
There is really no well-defined boundary between astronomy and space exploration. Most people would say that astronomy is observing what is in space while space exploration is actually sending a spacecraft there. However the space telescopes, the Hubble and James Webb, operate by observing but actually are spacecraft. The missions to the outer planets, such as Voyager I and II, went past the planets but didn't land on any, only taking photos and beaming them back to earth.
In contrast to astronomy, which is actually observing what is in space, cosmology is developing theories about the basic nature of the universe. Albert Einstein's two theories of Relativity, for example, are cosmology rather than astronomy. But there is a definite connection between the two as astronomical observations, as well as data like particle accelerator experiments, are used to verify cosmological theories.
It is not actually necessary to observe space. I spent a lot more time reading about space than actually observing it. My interest in science began when I took this children's book out of the school library at age 8.
EXPLORING STARS WITHOUT A TELESCOPE OR SPACESHIP
We can actually explore how a star works right here on earth. We know that there was once a large star that exploded in a supernova, since only the largest stars explode in a supernova. Some of the matter fell back together again, by gravity, to form the sun and planets. We know that the sun is such a second generation star because it contains heavier elements that are beyond it's current stage in the fusion process, which is fusing four hydrogen atoms into one helium atom.
Every atom in your body was once part of this star. Energy such as that in tides, geothermal energy, any energy derived from the rotation of the earth, the energy in moving glaciers, volcanoes, landslides and, radioactivity, all come from the explosion of this star.
Stars form when there is enough gravitational mass to overcome the mutually repulsive force between electrons and crunch smaller atoms together into larger ones. The new larger atom contains less internal energy than the atoms that were crunched together to form it. The excess energy is released as radiation and that is why stars shine.
A simple way to illustrate how stars work is to consider two or more spheres made of clay, with surface area representing their internal energy. If we combine the spheres together, into one large sphere, it will have less overall surface area than the smaller spheres. The lost surface area, that represents energy, is released as radiation and this is why stars shine.
A star is an equilibrium between the inward force of gravity and the outward force of the energy released by fusion. As successively heavier elements are fused together more energy per time is released. This upsets the equilibrium and the star explodes as a supernova, scattering it's matter across space. Some of the matter may fall back together, creating a solar system around a second generation star. This is almost certainly the only way that solar systems form.
We can see how this works just by looking at the earth. The most abundant element on earth by mass is iron, because the ordinary fusion process only goes as far as iron. Elements heavier than iron are only created by the energy released by the actual explosion of the supernova. This is why gold is rare while iron is common.
Some of these very heavy atoms that were forced together are less than stable and gradually emit particles or radiation to reach a more stable energy state. These emissions are known as radioactivity. Heavy rare earth elements are often found together in mines because they did not have the chance to separate by mass before the star exploded.
In the outer reaches of the star it makes sense that molecular fusion, rather than nuclear fusion, took place. This is what formed light molecules, like water and salt, which is why water and salt arrived together in comets. I believe that this happened when the outer layers of the previous star were blasted away in a nova, before the star exploded from the center in a supernova. This is also why the oxygen, nitrogen and, hydrogen in the atmosphere and water is diatomic. When hydrogen is used for fuel this is where the energy originated.
The earth is nowhere near massive enough to produce nuclear fusion and ignite as a star but it can accomplish molecular fusion by geological processes. This is how gems are formed inside the earth. Gems that refract light are very limited in size. This is because the atoms must be lined up for it to refract light. Geological processes can accomplish this but the gem is limited to being closer to the scale of the atoms than to the scale of the earth.
So we can take a close look at how stars work right here on earth.
