So, I have a question for my loyal readers (all four and that robot run by Google).
If you are going on a trip and decide to drive but you know that the airplane is going to fly with or without you, and that "your" seat is going to be empty, are you now producing the equivalent CO2 of flying+driving?
That is, the car you drive is producing X kg of CO2 for the trip, and there is an empty seat in an airplane and if you were in that seat, it would count as Y kg of CO2, are you responsible for X+Y kg of CO2, or just X kg of CO2?
I don't want to say what I think; I want your thoughts.
Before you answer, consider this scenario and question: You and your neighbor are part of the neighborhood watch and you are both going to the police station for a neighborhood watch meeting. Are you responsible for the emissions of both vehicles if your neighbor offers to carpool and you refuse?
Saturday, March 28, 2009
Friday, March 27, 2009
What is the name of the largest star?
Question from dear son:
What is the name of the largest star?
Well, for the moment, let us assume that we can only discuss stars that were named by humans. That is, there may be many stars larger than the one I am going to discuss, but we have not discovered them yet. If some other intelligent life form out in the universe has, we do not know about it...
The largest known star in terms of size, radius, diameter, whatever, is named VY Canis Majoris. VY Canis Majoris is between about 1800 and 2100 times larger than our sun.
DS wants to know why VY Canis Majoris is named as it is. The star is in the constellation Canis Major, thus its surname. From what I can tell, VY comes from the person who first cataloged the star, A.N. Vyssotsky. Yeah, that's helpful.
Vy Canis Majoris is a relatively cold star with a photosphere temperature of only about 3500 Kelvins (5840 degrees Fahrenheit). Our sun has a photosphere temperature of about 6000 kelvins, or about 11,000 degrees Fahrenheit. In general, the larger the star, the cooler its surface.
Someone with a six-year-old has already answered this question, and I'm going to steal one of their graphics. Go back to my post about Pluto and the graphic of the solar system. It's approximately to scale, with the sun off the screen. Here's our sun compared with Vy Canis Majoris. Vy CMa would reach past the orbit of Saturn.
Here's another graphic that shows relative sizes of celestial bodies. As you go from one frame to the next (say, 2 to 3), the last object in the first frame is the first object in the next frame. Going from 2 to 3, you see the size differences between Jupiter and the other planets and Jupiter and the sun and Sirius. This does not have VY Canis Majoris on it, but it'll be in the last frame, just a bit bigger than VV Cephei A.
Everything I've talked about so far has been in terms of radius, volume, whatever. Another measure of "size" is mass. VY Canis Majoris is only about 30 to 40 times as massive as our sun. The most massive stars that we know about include HD_269810, Eta Carinae, the Pistol Star, and WR102ka, each of which is about 150 times as massive as our sun. These massive, luminuous stars are expected to end in super novae in the next million years or so. Depending on the details of the super nova, these stars will either end as neutron stars or possibly black holes. A neutron star will form if what's left after the super nova is less than about three times the mass of the sun. Otherwise, a black hole will form.
Will our sun become a black hole?
No.
Our sun's evolution from now until about six billion years from now will be as follows:
In about four billion years, the hydrogen at the sun's core will be used up and it'll start fusing helium into carbon and oxygen. As this happens, it'll expand a great deal and become a red dwarf. Its surface will reach the orbit of Mercury. The sun will expand and contract several times during its red dwarf phase. At some point, about 30 million years after it becomes a red dwarf, the sun will expand out to Earth's orbit. When this happens, a large amount of material (up to about 50% of the sun's mass) will continue moving outward and will be lost to space.
After that happens, the core of the sun will collapse to about the size of the Earth. Because of its mass, it cannot collapse any further and it'll become a white dwarf, with a core temperature of more than 100,000 kelvins. Its density will be about a million times larger than the density of the earth, and its core will be carbon and oxygen. The white dwarf will cool, and after a very long time (hundreds to thousands of billions of years), it should become a cold lump of degenerate matter, called a black dwarf. None of these black dwarves should exist right now because the universe is only about 15 billion years old.
What is the name of the largest star?
Well, for the moment, let us assume that we can only discuss stars that were named by humans. That is, there may be many stars larger than the one I am going to discuss, but we have not discovered them yet. If some other intelligent life form out in the universe has, we do not know about it...
The largest known star in terms of size, radius, diameter, whatever, is named VY Canis Majoris. VY Canis Majoris is between about 1800 and 2100 times larger than our sun.
DS wants to know why VY Canis Majoris is named as it is. The star is in the constellation Canis Major, thus its surname. From what I can tell, VY comes from the person who first cataloged the star, A.N. Vyssotsky. Yeah, that's helpful.
Vy Canis Majoris is a relatively cold star with a photosphere temperature of only about 3500 Kelvins (5840 degrees Fahrenheit). Our sun has a photosphere temperature of about 6000 kelvins, or about 11,000 degrees Fahrenheit. In general, the larger the star, the cooler its surface.
Someone with a six-year-old has already answered this question, and I'm going to steal one of their graphics. Go back to my post about Pluto and the graphic of the solar system. It's approximately to scale, with the sun off the screen. Here's our sun compared with Vy Canis Majoris. Vy CMa would reach past the orbit of Saturn.
Here's another graphic that shows relative sizes of celestial bodies. As you go from one frame to the next (say, 2 to 3), the last object in the first frame is the first object in the next frame. Going from 2 to 3, you see the size differences between Jupiter and the other planets and Jupiter and the sun and Sirius. This does not have VY Canis Majoris on it, but it'll be in the last frame, just a bit bigger than VV Cephei A.Everything I've talked about so far has been in terms of radius, volume, whatever. Another measure of "size" is mass. VY Canis Majoris is only about 30 to 40 times as massive as our sun. The most massive stars that we know about include HD_269810, Eta Carinae, the Pistol Star, and WR102ka, each of which is about 150 times as massive as our sun. These massive, luminuous stars are expected to end in super novae in the next million years or so. Depending on the details of the super nova, these stars will either end as neutron stars or possibly black holes. A neutron star will form if what's left after the super nova is less than about three times the mass of the sun. Otherwise, a black hole will form.
Will our sun become a black hole?
No.
Our sun's evolution from now until about six billion years from now will be as follows:
In about four billion years, the hydrogen at the sun's core will be used up and it'll start fusing helium into carbon and oxygen. As this happens, it'll expand a great deal and become a red dwarf. Its surface will reach the orbit of Mercury. The sun will expand and contract several times during its red dwarf phase. At some point, about 30 million years after it becomes a red dwarf, the sun will expand out to Earth's orbit. When this happens, a large amount of material (up to about 50% of the sun's mass) will continue moving outward and will be lost to space.
After that happens, the core of the sun will collapse to about the size of the Earth. Because of its mass, it cannot collapse any further and it'll become a white dwarf, with a core temperature of more than 100,000 kelvins. Its density will be about a million times larger than the density of the earth, and its core will be carbon and oxygen. The white dwarf will cool, and after a very long time (hundreds to thousands of billions of years), it should become a cold lump of degenerate matter, called a black dwarf. None of these black dwarves should exist right now because the universe is only about 15 billion years old.
Wednesday, March 25, 2009
Women and science in history...today
Today as I was looking across the (one of four) conference room during a talk, something struck me.
I was not being blinded by a bunch of bald heads. In fact, there were a lot fewer balding, white men in the audience than young, fully covered heads. Many of these heads also sported a couple of feet of hair, and a reasonable amount of the skin under the heads was dark. While the sciences may be more liberal in its acceptance of long-haired hippy freaks, it is by no means dominated by them. Those with long hair here are, with few exceptions, female, and scientists never have time to go get a tan.
This is the first conference I've been to where it is clear that the old guard of white males has mostly died out. Now, it may be a little sad that these people are dieing, but I think it's great that they're not being replaced by the same people from a good-old-boy network.
To be sure, I'm not claiming that this group of old, white, balding men were awful (many of the one just starting to be gray and bald came of age during the feminist revolution of the 60s after all), but it is nice to see a much greater diversity than in the past.
Also, this trend is an actual trend. When I first started attending these meetings, pretty much everybody was male, old, white, bald, or had some combination of those "features."
I was not being blinded by a bunch of bald heads. In fact, there were a lot fewer balding, white men in the audience than young, fully covered heads. Many of these heads also sported a couple of feet of hair, and a reasonable amount of the skin under the heads was dark. While the sciences may be more liberal in its acceptance of long-haired hippy freaks, it is by no means dominated by them. Those with long hair here are, with few exceptions, female, and scientists never have time to go get a tan.
This is the first conference I've been to where it is clear that the old guard of white males has mostly died out. Now, it may be a little sad that these people are dieing, but I think it's great that they're not being replaced by the same people from a good-old-boy network.
To be sure, I'm not claiming that this group of old, white, balding men were awful (many of the one just starting to be gray and bald came of age during the feminist revolution of the 60s after all), but it is nice to see a much greater diversity than in the past.
Also, this trend is an actual trend. When I first started attending these meetings, pretty much everybody was male, old, white, bald, or had some combination of those "features."
Sunday, March 22, 2009
Is it more energy efficient to fly or to drive to your destination?
DW asked a question of me that was asked at Crunchy Chicken. Is it selfish to fly for tourism/pleasure?
Here's my take on this question. But first, it has to be framed in the "right" way.
Here's my way of asking the question, giving it two parts, each of which I will simplify into just talking about CO2 emissions at the vehicle.
1) Is it better for the environment for my family to drive or to fly to our vacation destination? Or not to go at all?
2) Is it better for the environment for me to drive or fly to a work meeting?
Let's start with 2) because it's a single person on travel and I often do not have the choice about going if I want to keep my job.
I was going to use this graphic, but it sucks. It's not clear how to account for three passengers or a ULEV vehicle.
Let's calculate based on estimates from various sources rather than a graphic. According to atmosfair.de, my business travel this week is likely to cost about 1080 kg CO2. I've read their documentation, and it seems light, but relatively well-done. It's certainly not a research article, but I don't think it's meant to be. I'm going to trust that it is approximately right.
The personal-vehicle travel, round-trip distance is about 3900 km (2400 miles). If I took my Prius, according to fueleconomy.gov, it would cost about 0.6 tonnes (metric tons) of CO2. It would also take me about 36 hours round-trip. If I took the business vehicle, an older Ford SUV, it would cost about 1.6 tonnes of CO2.
So, clearly, it would be best for the environment if I didn't go. It would probably also be best for the marriage if I didn't go (at least until I lost my job). Next best would be to drive the Prius. However, the above estimate only accounts for the CO2 cost of driving. I would need to spend at least one night each-way in a hotel. I don't want to go into the details of how much CO2 that would cost, but it would add a bit to the total trip cost. Driving the Prius may even come out to more than the air travel due to dining out for at least six meals, additional energy costs at the hotel, etc., etc., etc. I could mitigate some or a lot of that additional CO2 cost by camping and buying food from a grocer or farmer, but does anyone really think that would happen during a business trip? Perhaps if I knew the route well enough.
Now, let's answer 1). The three of us are planning a trip to Los Angeles this late Spring. Do we fly or do we drive? The round-trip driving distance is about 1600 km (1000 miles). The CO2 cost is about 0.2 tonnes of CO2, assuming 10% city and 90% freeway driving. The fueleconomy.gov estimate is almost certainly for a single driver, so let's assume that with the passengers, we double the weight of the driver, which only accounts for about 5% of the total weight (10% with the passengers). So, we would not change the total emissions by an appreciable amount.
The cost to fly? atmosfair.de claims that for three passengers, the cost would be about 1.3 metric tons of CO2 (a little over 0.4 per passenger).
So, again, it's cheaper in CO2 for us to drive our Prius. Now, the Prius is not a very common vehicle, so each person would need to do the calculation for their vehicle, but unless you drive an SUV, you are likely to put less greenhouse gas mass into the atmosphere if you drive. Also, an airplane puts the greenhouse gases into just about the worst place possible in terms of environmental damage.
Now, back to the original question. Is flying to a vacation destination selfish? Yes, of course it is. Now, that doesn't mean I think everyone needs to instantly stop traveling, but I do think people should be aware of their actions (admission is the first step or something like that). If you have to go on a long trip, you might also consider taking the train, which is much more efficient than flying.
Considering the amount of driving people in the USA do, I think we should focus on decreasing emissions from our personal vehicles (by using them less, by technology, by whatever means necessary) before we worry too much about that 10% or less effect our air travel has. Where do I get the 10%? Well, most people don't travel 1,000 miles by air for every 10,000 miles they drive. I suspect the number is much smaller. But, the total greenhouse gas emissions from air travel accounts for about 10% of transportation costs. So, not really pulling a number from my...thin air, the total amount of air travel-caused emissions is 10% or less for most people.
Driving three blocks to get groceries or coffee twice a week is much more of a selfish thing to do. I'm as guilty as everyone else.
Hi, My name is Moses and I'm a CO2 emitter.
Here's my take on this question. But first, it has to be framed in the "right" way.
Here's my way of asking the question, giving it two parts, each of which I will simplify into just talking about CO2 emissions at the vehicle.
1) Is it better for the environment for my family to drive or to fly to our vacation destination? Or not to go at all?
2) Is it better for the environment for me to drive or fly to a work meeting?
Let's start with 2) because it's a single person on travel and I often do not have the choice about going if I want to keep my job.
I was going to use this graphic, but it sucks. It's not clear how to account for three passengers or a ULEV vehicle.
Let's calculate based on estimates from various sources rather than a graphic. According to atmosfair.de, my business travel this week is likely to cost about 1080 kg CO2. I've read their documentation, and it seems light, but relatively well-done. It's certainly not a research article, but I don't think it's meant to be. I'm going to trust that it is approximately right.
The personal-vehicle travel, round-trip distance is about 3900 km (2400 miles). If I took my Prius, according to fueleconomy.gov, it would cost about 0.6 tonnes (metric tons) of CO2. It would also take me about 36 hours round-trip. If I took the business vehicle, an older Ford SUV, it would cost about 1.6 tonnes of CO2.
So, clearly, it would be best for the environment if I didn't go. It would probably also be best for the marriage if I didn't go (at least until I lost my job). Next best would be to drive the Prius. However, the above estimate only accounts for the CO2 cost of driving. I would need to spend at least one night each-way in a hotel. I don't want to go into the details of how much CO2 that would cost, but it would add a bit to the total trip cost. Driving the Prius may even come out to more than the air travel due to dining out for at least six meals, additional energy costs at the hotel, etc., etc., etc. I could mitigate some or a lot of that additional CO2 cost by camping and buying food from a grocer or farmer, but does anyone really think that would happen during a business trip? Perhaps if I knew the route well enough.
Now, let's answer 1). The three of us are planning a trip to Los Angeles this late Spring. Do we fly or do we drive? The round-trip driving distance is about 1600 km (1000 miles). The CO2 cost is about 0.2 tonnes of CO2, assuming 10% city and 90% freeway driving. The fueleconomy.gov estimate is almost certainly for a single driver, so let's assume that with the passengers, we double the weight of the driver, which only accounts for about 5% of the total weight (10% with the passengers). So, we would not change the total emissions by an appreciable amount.
The cost to fly? atmosfair.de claims that for three passengers, the cost would be about 1.3 metric tons of CO2 (a little over 0.4 per passenger).
So, again, it's cheaper in CO2 for us to drive our Prius. Now, the Prius is not a very common vehicle, so each person would need to do the calculation for their vehicle, but unless you drive an SUV, you are likely to put less greenhouse gas mass into the atmosphere if you drive. Also, an airplane puts the greenhouse gases into just about the worst place possible in terms of environmental damage.
Now, back to the original question. Is flying to a vacation destination selfish? Yes, of course it is. Now, that doesn't mean I think everyone needs to instantly stop traveling, but I do think people should be aware of their actions (admission is the first step or something like that). If you have to go on a long trip, you might also consider taking the train, which is much more efficient than flying.
Considering the amount of driving people in the USA do, I think we should focus on decreasing emissions from our personal vehicles (by using them less, by technology, by whatever means necessary) before we worry too much about that 10% or less effect our air travel has. Where do I get the 10%? Well, most people don't travel 1,000 miles by air for every 10,000 miles they drive. I suspect the number is much smaller. But, the total greenhouse gas emissions from air travel accounts for about 10% of transportation costs. So, not really pulling a number from my...thin air, the total amount of air travel-caused emissions is 10% or less for most people.
Driving three blocks to get groceries or coffee twice a week is much more of a selfish thing to do. I'm as guilty as everyone else.
Hi, My name is Moses and I'm a CO2 emitter.
Wednesday, March 18, 2009
Happy Women in History Month
March is Women in History Month, here in the US, so clearly I need to discuss the history of women in math and science. There is zero chance that I could name even 0.0000001% of the women who have been influential in science and mathematics, so I'm going to name a few who have made a difference in my view, mostly because they were absolutely phenomenal scientists. I will not name any living, women scientists who directly affected me, but there were many, and I think that most of them know how influential they were.
The women I mention below overcame great, artificial barriers to do their work. In my opinion, anyone who says women cannot do science or math as well as men should be removed from public life permanently. Mr. Summers, I'm looking at you and Barbie, in particular. There is absolutely no evidence that, given the same support and resources, women do not thrive as well as or better than men in any field. If you disagree, you are irrelevant and can go elsewhere; I'm not interested in your opinion.
Back to celebrating, with my favorite first.
Dr. Marie Curie (1867-1934)
Marie Curie is the scientist that inspired my love of science. When I was about six or seven, I read a book about her and decided that science and math would be my future. She studied radioactivity (coined the term and has a unit of measure--the Curie---named after her), discovered the elements radium and polonium, and pioneered the use of radioactive isotopes in the treatment of cancer. She became the first female professor at the University of Paris, and was the first person to be awarded two Nobel prizes.
In 1903, she was awarded, along with her husband Pierre Curie and Henri Becquerel, the Nobel Prize in Physics for their work on radiation. This was the first time a woman was awarded a Nobel Prize. In 1911, she was awarded a second Nobel Prize (and did not share it), this time in chemistry,
Her graduate student, Marguerite Perey, was the first woman to be elected to the French Academy of Sciences (Dr. Curie was refused the honor in 1911 because of sexism).
She was, is, and should continue to be an inspiration to all scientists.
Dr. Jane Goodall (1934 - present)
Jane Goodall began studying the chimpanzees in Gombe Stream National Park in Tanzania, in 1960 and continued for 45 years (I'm not sure that she's done even now). She was the first scientist to observe the creation of tools in non-humans; previously, it was known that non-humans could use tools, but that only humans were sophisticated enough to make them. She has contributed much to the field of primatology over her 45 years, and I can only hope that I will be able to put up with the scientific community for half that long.
In 1974, she founded the Jane Goodall Institute, which is active in protecting the environment.
Dr. Goodall has written too many books to list, including many children's books.
Florence Nightingale (1820 - 1910)
Florence Nightingale pioneered the use of hygiene and sterilization in military field hospitals during the Crimean War. It was her work to clean up a medical barracks in Istanbul that caused the death rate there to drop from ~43 per cent to 2 per cent. She developed a very strong desire to move health care away from cold, impersonal, crowded hospitals to the patients' homes.
In 1859, Nightingale was elected the first female member of the Royal Statistical Society.
Rear Admiral Grace Hopper, Ph.D. (1906 - 1992)
Grace Hopper was at the forefront of computer development in the 40s. She earned her Ph.D. in mathematics at Yale in 1934 and taught at Vassar from 1931 to 1943, when she joined the US Navy Reserves, where she served on the Mark I programming staff. She essentially invented the compiler, which is a bit of software that translates a human-readable programming language into machine language. COBOL, the business programming language still in use today, was based on her compiler FLOW-MATIC. She pioneered the use of reusable computer code (reducing errors and making software extensible), and was one of the developers of UNIVAC I.
More:
Dr. Lisa Randall
Dr. Rosalind Franklin
Hypatia
Mary Somerville
Caroline Herschel
Carolyn Shoemaker
Dr. Sally Ride
Dr. Olivia Judson
There are, of course, many, many more, but here's my problem: I don't have the space to talk about each and every famous influential woman in science and mathematics. Or even about my favorites. :( This page is already getting long and I'm feeling guilty about having to choose one over the others.
I may try to post some about some other people during this month. We'll see how time works out. If you have a favorite (or several), post in a comment and I will look her up and post a paragraph or so when time allows.
The women I mention below overcame great, artificial barriers to do their work. In my opinion, anyone who says women cannot do science or math as well as men should be removed from public life permanently. Mr. Summers, I'm looking at you and Barbie, in particular. There is absolutely no evidence that, given the same support and resources, women do not thrive as well as or better than men in any field. If you disagree, you are irrelevant and can go elsewhere; I'm not interested in your opinion.
Back to celebrating, with my favorite first.
Dr. Marie Curie (1867-1934)
Marie Curie is the scientist that inspired my love of science. When I was about six or seven, I read a book about her and decided that science and math would be my future. She studied radioactivity (coined the term and has a unit of measure--the Curie---named after her), discovered the elements radium and polonium, and pioneered the use of radioactive isotopes in the treatment of cancer. She became the first female professor at the University of Paris, and was the first person to be awarded two Nobel prizes.
In 1903, she was awarded, along with her husband Pierre Curie and Henri Becquerel, the Nobel Prize in Physics for their work on radiation. This was the first time a woman was awarded a Nobel Prize. In 1911, she was awarded a second Nobel Prize (and did not share it), this time in chemistry,
"in recognition of her services to the advancement of chemistry by the discovery of the elements radium and polonium, by the isolation of radium and the study of the nature and compounds of this remarkable element"She is only one of two people to receive a Nobel Prize in two different fields. The other is male and is therefore irrelevant to this discussion.
Her graduate student, Marguerite Perey, was the first woman to be elected to the French Academy of Sciences (Dr. Curie was refused the honor in 1911 because of sexism).
She was, is, and should continue to be an inspiration to all scientists.
Dr. Jane Goodall (1934 - present)
Jane Goodall began studying the chimpanzees in Gombe Stream National Park in Tanzania, in 1960 and continued for 45 years (I'm not sure that she's done even now). She was the first scientist to observe the creation of tools in non-humans; previously, it was known that non-humans could use tools, but that only humans were sophisticated enough to make them. She has contributed much to the field of primatology over her 45 years, and I can only hope that I will be able to put up with the scientific community for half that long.
In 1974, she founded the Jane Goodall Institute, which is active in protecting the environment.
Dr. Goodall has written too many books to list, including many children's books.
Florence Nightingale (1820 - 1910)
Florence Nightingale pioneered the use of hygiene and sterilization in military field hospitals during the Crimean War. It was her work to clean up a medical barracks in Istanbul that caused the death rate there to drop from ~43 per cent to 2 per cent. She developed a very strong desire to move health care away from cold, impersonal, crowded hospitals to the patients' homes.
"my view you know is that the ultimate destination is the nursing of the sick in their own homes. … I look to the abolition of all hospitals and workhouse infirmaries. But it is no use to talk about the year 2000."Nightingale believed in and heavily used a data-based approach to determining how well hospitals and health care officials were caring for their patients. She was one of the first health care professionals who gathered and analyzed copious amounts of statistical data throughout her career. To present the results of her work in tracking deaths due to needlessly poor conditions, Nightingale developed the Polar-area Diagram, also known as the Rose Diagram. This diagram was derived from the pie chart, but is actually useful in comparing multiple data sets (the pie chart is just about the most useless way of presenting data imaginable).
In 1859, Nightingale was elected the first female member of the Royal Statistical Society.
Rear Admiral Grace Hopper, Ph.D. (1906 - 1992)
Grace Hopper was at the forefront of computer development in the 40s. She earned her Ph.D. in mathematics at Yale in 1934 and taught at Vassar from 1931 to 1943, when she joined the US Navy Reserves, where she served on the Mark I programming staff. She essentially invented the compiler, which is a bit of software that translates a human-readable programming language into machine language. COBOL, the business programming language still in use today, was based on her compiler FLOW-MATIC. She pioneered the use of reusable computer code (reducing errors and making software extensible), and was one of the developers of UNIVAC I.
More:
Dr. Lisa Randall
Dr. Rosalind Franklin
Hypatia
Mary Somerville
Caroline Herschel
Carolyn Shoemaker
Dr. Sally Ride
Dr. Olivia Judson
There are, of course, many, many more, but here's my problem: I don't have the space to talk about each and every famous influential woman in science and mathematics. Or even about my favorites. :( This page is already getting long and I'm feeling guilty about having to choose one over the others.
I may try to post some about some other people during this month. We'll see how time works out. If you have a favorite (or several), post in a comment and I will look her up and post a paragraph or so when time allows.
Monday, March 16, 2009
Sunday, March 15, 2009
Planets...
DM-i-L asked what's the real difference between a dwarf planet and a planet.
The IAU specification's only real difference is that the dwarf planet has not cleared its orbit. Clearing an orbit refers to removal of all small debris and most large debris from the region through which the object passes on its orbit around the star. This removal involves incorporating all of that debris into the main body or gravitationally accelerating it out of the region.
Earth has cleared its orbit of all but a few large objects. First, of course is Luna. Second, there is at least one and probably several small objects in a horseshoe orbit around Earth. Other than that, the path that Earth takes around the sun is clear. The same is true for the other seven planets:
Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune.
The named dwarf planets, Ceres, Pluto, Eris (2003 UB313), Haumea, and Makemake (not pronounced as "make, make" but as "mocky mocky") all have other debris in their orbits.
But, what about Saturn and its dust and rings? Well, Saturn is gravitationally in control of all that junk; there's basically nothing in its orbit that isn't strongly affected by Saturn.
There are currently only eight planets in our solar system. There are hundreds of known extrasolar (out of our system) planets.
The IAU specification's only real difference is that the dwarf planet has not cleared its orbit. Clearing an orbit refers to removal of all small debris and most large debris from the region through which the object passes on its orbit around the star. This removal involves incorporating all of that debris into the main body or gravitationally accelerating it out of the region.
Earth has cleared its orbit of all but a few large objects. First, of course is Luna. Second, there is at least one and probably several small objects in a horseshoe orbit around Earth. Other than that, the path that Earth takes around the sun is clear. The same is true for the other seven planets:
Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune.
The named dwarf planets, Ceres, Pluto, Eris (2003 UB313), Haumea, and Makemake (not pronounced as "make, make" but as "mocky mocky") all have other debris in their orbits.
But, what about Saturn and its dust and rings? Well, Saturn is gravitationally in control of all that junk; there's basically nothing in its orbit that isn't strongly affected by Saturn.
There are currently only eight planets in our solar system. There are hundreds of known extrasolar (out of our system) planets.
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