Common Misconceptions About Astronomy
By Liam McDaid Sacramento City College
1). Whither seasons? Seasons are caused by Earth changing its distance from the Sun as it orbits the Sun.
It is true that Earth changes its distance from the Sun over the course of a year, but the change is about 3%. It's pretty clear that the temperature changes on Earth from season to season (in many places) much more than 3%. Also, most people are vaguely aware that the Southern Hemisphere has different seasons from the Northern Hemisphere, "they" have winter when "we"
have summer. If that's true, how can it be connected to the distance between the Earth and Sun?
If distance to the Sun played a major role in the seasons, then all Earth should have the same seasons at the same time.
So what causes the seasons? Ah... that would be the tilt of Earth. As we spin, we have a tilt (from the Sun's point of view) of about 23°. This means that sometimes North Earth is tilted toward the Sun and sometimes tilted away (and vice versa for South Earth). If you're wondering why that matters, consider this: When the Sun is higher in our sky, the light it shines is more concentrated - think how sunlight around sunset doesn't warm you much compared to sunlight at noontime. Also, when the Sun is higher in the sky, it stays up longer because it appears to follow a longer path (Earth is really doing the moving here) and takes longer to go from one end of that path (sunrise) to the other (sunset).
2). Shooting deathstars: If stars are so enormous in size, then why don't shooting stars destroy Earth?
Because shooting stars aren't really stars. They're bits of debris that usually vaporize in Earth's atmosphere. Bigger bits might make it to the ground and become meteorites. Real big bits (10 km across or more) do things like take out the dinosaurs and cause mass-extinctions. There have been five of those in the last half-billion years.
3). Dark side of the Moon: The Moon has a "dark" side that is in eternal darkness.
The Moon is lit up about half the time and in darkness about half the time, just like any other moon, planet or piece of debris in our Solar System. No body in the Solar System has a large part of itself in permanent darkness. When we see the phases of the Moon change, we are watching the changing day on the Moon. If the face of the moon changes its lighting over the course of a month, then how can half of the Moon be in eternal darkness? Now there are small parts of the Moon near its south and north poles where sunlight never reaches into some craters, but that's not the same thing, is it?
Now if you're wondering if a planet could have a permanently dark side, then read the next one...
4). Far Side = Dark Side: The Moon's dark side is the side we can never see.
We only see one face of the Moon. This is because the Moon spins in a way that it takes the same amount of time to spin around once as the Moon takes to move (revolve) around the Earth.
In a way, the Moon's "day" is the same as its "year" - so we only see the side of the Moon that faces us. No matter where on Earth you are, the same face of the Moon stares down at us. This is called the near side. If you want to see the far side of the Moon, you have to go there: the first humans to see it with their eyes were the astronauts of Apollo 8. The far side gets lit by the Sun the same as the near side, just at different times. During New Moon, the far side is completely lit up and the near side is in darkness.
Now if the Moon keeps the same face pointed toward Earth (this is also true of many moons of Jupiter and Saturn), then shouldn't it be possible for a planet to always keep one face toward the Sun thus making the far side of this planet the "dark side"? Yes, it's possible. The only planet that might do this is Mercury, and astronomers used to think this happened there. But it doesn't, because of the nature of Mercury's orbit around the Sun. Still, it could be happening with some distant world orbiting a far star.
5). Neighboring stars: Getting from one star system to another only takes a few days.
As seductive as the idea of faster-than-light travel is, there's no evidence that it's possible.
When I say that, I don't mean that there's some widget we need to invent and then it's all good. I mean not possible. If we could find a way to take shortcuts through space (wormholes,
hyperspace, etc.) that would be cool too, but the jury's out on whether that's possible. This means the stars may be beyond our practical reach, unless a human culture emerges that plans far into the future.
Stars are millions of times further away than even the most distant planet in our Solar System.
The space between stars is so huge compared to their sizes that when entire galaxies with hundreds of billions of stars collide, only a few stars actually physically collide. A few, out of hundreds of billions. This enormous void takes tens of thousands of years for our fastest space probes to reach only the nearest star.
About one-third of all stars come in sets (binaries or multiples). Even for multiple stars, the spaces between them are large or else they would be at risk of colliding. As an example, the star Sirius (in Canis Major) is actually two stars that orbit each other. They are as far apart from each other as the Sun and Uranus are. Other multiple stars have still greater distances between them, such as Rigel (in Orion).
6). The North Star: It's the brightest star in the sky.
Many people are taught this in school, but not by astronomers. A clear night can quickly settle this. At that time, go outside. Look up in the sky toward the north (if you're not sure what direction this is, map your house on Google, or watch the sunset - North is to the right of it). If you see stars in the northern sky, one of them is likely the North Star - it's true name is Polaris (in Ursa Minor). Now, turn around and look to the southern sky. Do you see anything brighter than the stuff in the northern sky? Odds are you will.
In the days pre-GPS, Polaris was important for navigation because of its location in the sky, not its brightness. It is very close to the North Celestial Pole (NCP) , or the north pole of the sky.
All the sky turns around that point (or its equivalent in the southern sky - the South Celestial Pole). Since the NCP is pretty important in finding your way, Polaris is important by
association.
7). Moon phases: They're caused by the shadow of Earth.
When part of the Moon is in darkness, that's just because that part is out of view of the Sun and so that part is having its night. The Earth is only half-lit by the Sun at any time, why should the Moon be different? The Moon does take much longer to spin around once than Earth, and that is what we see when watch the phases over the course of a month - which is how long the Moon's "day" is.
The shadow of Earth does cross the Moon during a lunar eclipse, but this can only happen during a full moon - when the Earth can get in the way between the Sun and Moon. It also only happens at most, a couple times a year.
8). Astrology and Astronomy: They're basically the same thing.
No. To a math phobic person, astrology might seem like a science because it uses extensive math to calculate things like planet positions and hour angles. Numerology does as well, yet it's certainly not a science. Astronomy, on the other hand is a science - not because of its use of math, but because it creates testable ideas about the Universe. Astronomers then go out and test those ideas. Some turn out to be based in reality, but many more do not. In science, ideas that don't correspond to what we see as reality are junked. Some think this is small minded but if there's anything to the idea, at some point in the future as our knowledge expands it will return in one form or another to make its presence known. Some ideas however, have stayed in the junk pile for centuries. Astrology is one such idea…When people test an idea, have it fail, and then continue to make excuses that allow the idea to go on, that's not science…
Astrology has been tested extensively in the 20th century and has failed again and again and again. Astrologers continue to excuse these huge failures but then as mentioned above, that shows that they don't do science. It makes more sense to think of Astrology as a very old religion that requires math skills if you practice it - as opposed to just believing in it which
requires no math. For more information about astrology from an astronomer's point of view, go here.
9). Free in orbit: Satellites aren't affected by Earth's gravity.
Things that orbit the Earth (or Moon, or anything) are very much affected by the gravity of what they are orbiting. Gravity is actually what makes them orbit. When you are in orbit, you are basically aiming for the ground and constantly missing (how the Hitchhiker's Guide to the Galaxy defines flying). In orbit you have enormous horizontal speed. The ground below curves beneath you faster than you can fall to hit it, so you never catch up. If there were no gravity at all in space, once a probe got there, it would move away from its planet of origin at a constant speed in a straight line. It wouldn't come back and it wouldn't be in orbit.
The reason there seems to be no gravity in the orbiting International Space Station is that you, it, your stuff, and everything else around you are falling at the same rate. You feel weightless because you are falling (and you feel it, constantly). If you jumped off a cliff, you would also feel weightless until you hit the ground. The difference is that things in orbit never hit the ground unless something gets in their way.
10). A young Universe: The Universe is only a few thousand years old.
As mentioned above, people that persist in making excuses to maintain ideas that have failed testing are not doing science. There are those who claim evidence to support a young Universe (and therefore a young Earth). The problem with all this claimed evidence is that it doesn't stand up to even basic investigation. These people often quote scientists to support their claims. The problem is, either the work quoted was done long ago (when we thought different), or
information is quoted out of context (so are some scientists), or it's a (usually not honest) misunderstanding of something in physics or astronomy. Since almost all people pushing this idea have a flamingly obvious agenda, this claim is not taken seriously by scientists. Is this close-minded? No more so than dismissing claims by some people - still made today - that Earth is actually flat. Some ideas don't reflect reality no matter how much some may wish.
So what about the evidence that the Universe is ancient? Just sampling some of the massive scientific work, let's start with the most abstract and move toward more concrete things. Based on the expansion of the Universe, you can make a crude guess as to when it all started based on the speed at which it now expands. This assumes that the expansion is constant, which it probably isn't, but I did say crude guess. From this, the Universe is between 10 billion and 20 billion years old.
Next, we can see the echo of the Big Bang in the Cosmic Background Radiation which is a kind of glowing leftover from that unimaginably violent event. Recent examinations of this glow tell us that the Universe is about 13.7 billion years old, assuming that the models used in these studies are correct. The point is, it doesn't disagree with the earlier value. If we found stars that are older than the Universe, then there's a problem with the model.
We have a good understanding of how stars work, how long they live and when they will die (see #19). We can build star models from this to estimate star ages. All around us in the Galaxy are many stars of ages from the newly born to the dying (or even dead). The measurable features that we look for in stars of certain ages agree with the predictions of our star models. From this, we know that the Sun is about 4.6 billion years old and the oldest stars in the Galaxy are about 13 billion years old. So far, so good...as the ages don't contradict each other and they are both younger than the oldest age of the Universe.
Meteorites can be dated radiometrically just like Earth rocks, and the oldest ones found so far (including rocks brought back from the Moon) are about 4.5 billion years old. So the Solar System isn't older than the Sun, which agrees again. Although we can't find rocks on Earth older than about 3.8 billion years because of Earth's active geology, no Earth, Mars or Moon rock has been found that is older than the Sun.
The point of all this is that the Universe, Sun, Moon and the planet beneath your feet are billions of years old. So it's an ancient Universe for such a young species as we to live in.
Perhaps there are species out there who have been around since the formation of the Sun. I'm sure they have some stories!
11). The polymorphous Zodiac: The planets travel through only 12 constellations
Constellations are arbitrary patterns humans read into the stars we see in the sky. Most of the constellations used in astronomy are from the Middle East by way of Greece and Rome. Other cultures of course, have different constellations. The Sun, Moon and planets travel through a specific band in the sky called the Zodiac. The planets and the Sun travel pretty close to a line in the middle of the Zodiac called the ecliptic, although the Moon's path wanders further. The classical zodiac has twelve constellations. This isn't a mystery, as the year has twelve months for the same reason - it's how many times the Moon goes around the Earth in a year (give or take).
With twelve constellations, the Sun is in a different one each month. It doesn't work well, because the number of months in a year doesn't divide evenly and this fact drove ancient skywatchers nuts - and leaving leftover days in their calendars.
There are 88 constellations and actually thirteen of them are on the ecliptic. The 13th one is Ophiuchus. If we allow for the tilt of the Moon's orbit, there are about twenty zodiacal
constellations. Some constellations that can host the Moon (and some planets) but aren't thought of as part of the Zodiac include Auriga, Orion and Crater.
So how many constellations are on the Zodiac? Depends on what sky object you care about.
The Sun has thirteen along its path, the Moon has about twenty. If this seems quite arbitrary, it is. Remember that all constellations are random patterns invented by humans, which is why they're not imbued with a deeper significance. Those who believe astrology is real think otherwise but see #15 for more about that.
12). Lunar phase names: A first quarter moon is 25% lit up.
Some names stick even when they make no sense. Lunar phases have two points named quarters: First Quarter and Last (or Third) Quarter. It's a source of huge confusion that when the Moon is in a "quarter" phase it's half lit by the Sun. The problem is that the word quarter doesn't refer to the illumination of the Moon, it refers to which of four main stages the lunar cycle is in (hence quarters). Each month has about four weeks because they are stand-ins for the phases of the moon. There are four quarters in the total lunar cycle, so each week represents one quarter of the cycle. In order, they are:
New Moon
First quarter Moon Full Moon
Third or Last quarter
New Moon (start of a new cycle)
The phase of the Moon where it's more than half lit (from our point of view) is called gibbous.
13). Is that all there is? Visible light is the only light.
The idea of invisible light sounds contradictory, but think about it: you can feel heat - which is a form of infrared light. You can also feel the aftereffects of ultraviolet light via a sunburn.
These are forms of light you can't see, but you can feel (either immediately or later). The amount of light in the Universe that we can't see dwarfs the tiny range of colors that we do see.
The types of light that humans can't see also include radio (which is light, not sound), x-rays, gamma rays, and microwaves (a type of radio light). These types of light can be detected, but not with human eyes. Many wonder if any aliens out there can see this other light with whatever organ they have that's equivalent to our eyes. Who knows? X-rays and gamma rays are
dangerous or outright lethal (sorry to any Incredible Hulk fans), so it's unlikely an alien species would be able to "see" them, but radio, infrared and ultraviolet are quite possible.
14). The lesser light: The Moon can only be seen during the night.
Most people don't look up in the sky unless there's a reason to. This is a major reason for most UFO reports - most people reporting them have minimal or no sky familiarity. During the day when the Sun is out it makes less sense to take time out of your busy day to watch the sky.
Because of this, most people are unaware that the Moon is often visible in the sky during the day.
Two good times to go moon watching during the day are: 1). A few hours before sunset when the Moon is past the phase of First Quarter but isn't yet Full. The Moon will be in the east in the late afternoon while the Sun is in the west. 2). Early in the morning a few days after the Moon is Full, but before Last Quarter. At this time, the Moon is in the west. The closer to full the Moon is, the more of it is lit up and the easier it is to see during the day.
The Sun and Moon are not the only things visible during the day. It is possible to see Venus in the sky during the day - if you know exactly where to look. The easiest way to do this is to see Venus before dawn and track it across the sky as the day goes on. From time to time you may lose it, but if you know the area of the sky it's in, you can find it again.
15). Bigger is better: The most important thing telescopes do is magnify stuff.
At star parties and observatories all across the land, The Question is asked: How much magnification does your telescope have? I always respond by asking "What magnification would you like it to be?" Changing the magnification takes no more time than it takes to change the eyepiece. The problem with high magnification is that you get a bigger image, but it's fainter. A large image is also blurrier. With bad seeing, a big image of Saturn quickly becomes a blurry washed out mess.
The most important thing telescopes do is gather light which is why they're often called light buckets. With more light, you can see fainter things or more detail in brighter things. The larger the light gathering surface (lens or mirror), the better. This is why we try to make telescopes with the largest light gathering surfaces possible, although some folks in Europe are carrying this to extremes.
From: http://scc.losrios.edu/~sah/physics/44Miscon.htm