H.A.L. Astronomy School

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Size and Distance Matters:. Or, Matters of Size and Distance in the Solar System and the Universe. If the Earth was a peppercorn

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H.A.L. Astronomy School

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1. H.A.L. Astronomy School Welcome back again if you are a returning student to the H.A.L. Astronomy! If you are new, you are also welcomed! If this is your first time the following information will be usefyl to you. H.A.L. Astronomy School is a non-linear, non-sequential series of half-an-hour presentations made by various members of the Howard Astronomical League on subjects that we feel will be of interest to beginning and intermediate amateur astronomers. We operate strictly by the clock showing atomic time, EDT. We always start precisely on time and we conclude each lesson before or, at least, by 7:30pm EDT when the regular monthly H.A.L. meeting begins. We try to pick topics that are interesting to beginners and intermediate amateur astronomers and we hope we strike a balance each month of fun and educational presentations. Anyone is welcome to instruct at H.A.L. Astronomy School. Just contact anybody who is one of your elected officers and make your wishes known.Welcome back again if you are a returning student to the H.A.L. Astronomy! If you are new, you are also welcomed! If this is your first time the following information will be usefyl to you. H.A.L. Astronomy School is a non-linear, non-sequential series of half-an-hour presentations made by various members of the Howard Astronomical League on subjects that we feel will be of interest to beginning and intermediate amateur astronomers. We operate strictly by the clock showing atomic time, EDT. We always start precisely on time and we conclude each lesson before or, at least, by 7:30pm EDT when the regular monthly H.A.L. meeting begins. We try to pick topics that are interesting to beginners and intermediate amateur astronomers and we hope we strike a balance each month of fun and educational presentations. Anyone is welcome to instruct at H.A.L. Astronomy School. Just contact anybody who is one of your elected officers and make your wishes known.

2. Size and Distance Matters: Or, Matters of Size and Distance in the Solar System and the Universe Last month we discussed “The Ones That Moved” and detailed the retrograde orbit of asteroid Vesta as well as the retrograde orbit Mars is about to exhibit. Tonight’s topic is “Size and Distance Matters: Or, Matters of Size and Distance in the Solar System and the Universe”.Last month we discussed “The Ones That Moved” and detailed the retrograde orbit of asteroid Vesta as well as the retrograde orbit Mars is about to exhibit. Tonight’s topic is “Size and Distance Matters: Or, Matters of Size and Distance in the Solar System and the Universe”.

3. If the Earth was a peppercorn… Then the Moon would be the size of a head of a pin 2.5” away from the Earth And the Earth/Moon combination would orbit a volleyball-sized Sun at a distance of 78 feet! We begin with two demonstrations that illustrate the need to be fully conscious intellectually when we start talking about distances out to planets, moons, our sun and all the other stars and galaxies. One shows scale within the solar system; the other shows scale within the galaxy.We begin with two demonstrations that illustrate the need to be fully conscious intellectually when we start talking about distances out to planets, moons, our sun and all the other stars and galaxies. One shows scale within the solar system; the other shows scale within the galaxy.

4. The Scale of the Galaxy Incredible Astronomy Demonstration #2 We now demonstrate the scale of the galaxy with Incredible Astronomy Demonstration #2.We now demonstrate the scale of the galaxy with Incredible Astronomy Demonstration #2.

5. The Scale of the Solar System If the Sun, our local daytime star (we never see the sun at nightl we can only see other distant suns at night), were modeled as the size of an English Pea and placed in the center of Times Square, New York…If the Sun, our local daytime star (we never see the sun at nightl we can only see other distant suns at night), were modeled as the size of an English Pea and placed in the center of Times Square, New York…

6. The Scale of the Solar System …then the nearest star (or distant sun since the terms are synonymous) would be another English Pea located in the middle of the Ginza in Tokyo. This distance scales out to 4.22 light years and the next nearest distant sun is, of course, currently Proxima Centauri.…then the nearest star (or distant sun since the terms are synonymous) would be another English Pea located in the middle of the Ginza in Tokyo. This distance scales out to 4.22 light years and the next nearest distant sun is, of course, currently Proxima Centauri.

7. Let’s look, then, in considerably more detail at the mathematical and emotional meaning of these two common astronomical terms, the AU, or astronomical unit and the light-year. We’ll do this by comparing the dimensions of the solar system (which will contain a few surprises) to a single light year which, as I am sure you know, is a unit of distance measure and NOT a unit of time. You have a single-page handout to which we will now refer. It is a simple thought experiment that can be done by anybody with a standard four-function calculator, or, in this case, a Microsoft Excel worksheet. No special intelligence is required other thatn the ability to think fairly clearly.Let’s look, then, in considerably more detail at the mathematical and emotional meaning of these two common astronomical terms, the AU, or astronomical unit and the light-year. We’ll do this by comparing the dimensions of the solar system (which will contain a few surprises) to a single light year which, as I am sure you know, is a unit of distance measure and NOT a unit of time. You have a single-page handout to which we will now refer. It is a simple thought experiment that can be done by anybody with a standard four-function calculator, or, in this case, a Microsoft Excel worksheet. No special intelligence is required other thatn the ability to think fairly clearly.

8. Before we dive into the worksheet here is a live presentation from the freeware Celestia software package. I have used Celestia before in HAL Astronomy School and find that it does many, many things useful in the teaching of astronomy. It is free for the downloading. You need a fast chip and graphics card to run it.Before we dive into the worksheet here is a live presentation from the freeware Celestia software package. I have used Celestia before in HAL Astronomy School and find that it does many, many things useful in the teaching of astronomy. It is free for the downloading. You need a fast chip and graphics card to run it.

9. This month’s Sky and Telescope has a review of a new book on the solar system by Nigel Hey. The reviewer says, “….”This month’s Sky and Telescope has a review of a new book on the solar system by Nigel Hey. The reviewer says, “….”

10. With that solar system background refresher let’s look at the worksheet now.With that solar system background refresher let’s look at the worksheet now.

11. Conclusion The diameter of the solar system is nowhere close to being measurable in terms of light years, even a single light year! It is not 1/10th, 1/100th, or even 1/1,000th of a light year! The diameter of the solar system is, at best, around 16/10,000th of one light year (0.0016)! It is, however, on average, around 12/10,000th (0.0012) of a light year. Our conclusion then is “….”Our conclusion then is “….”

12. Or is It? What is the Actual Extent of the Solar System? And by Logical Extension… What Might Be the Actual Extent of Other Solar Systems? Or, Where Do Solar Systems End? How Far Away from the Primary Star(s) Do They Extend? [Read slide.][Read slide.]

13. This illustration depicts the immensity of the Oort cloud. The radius is approximately 30 trillion kilometers, the Sun being the center point. Trillions of icy objects travel this region, relicts of the primordial solar nebula from which the solar system was formed, and the source of future long-period comets to the inner solar system. Remember to consider the Oort cloud as a sphere, not a torus and not a belt. In 1950 Jan Oort noticed three things about comets: No comet has been discovered with an orbit that indicates that it came from interstellar space, (2) There is a strong tendency for aphelia of long-period comet orbits to lie at a distance of about 50,000 AU, and (3) There is no preferential direction from which comets come. From this he proposed that comets reside in a vast cloud at the outer reaches of the solar system. The statistics imply that it may contain as many as a trillion comets. Unfortunately, since the comets are so small and at such large distances, we have no direct evidence about the Oort cloud.This illustration depicts the immensity of the Oort cloud. The radius is approximately 30 trillion kilometers, the Sun being the center point. Trillions of icy objects travel this region, relicts of the primordial solar nebula from which the solar system was formed, and the source of future long-period comets to the inner solar system. Remember to consider the Oort cloud as a sphere, not a torus and not a belt. In 1950 Jan Oort noticed three things about comets: No comet has been discovered with an orbit that indicates that it came from interstellar space, (2) There is a strong tendency for aphelia of long-period comet orbits to lie at a distance of about 50,000 AU, and (3) There is no preferential direction from which comets come. From this he proposed that comets reside in a vast cloud at the outer reaches of the solar system. The statistics imply that it may contain as many as a trillion comets. Unfortunately, since the comets are so small and at such large distances, we have no direct evidence about the Oort cloud.

15. The 52 AU maximum orbit of Pluto and Neptune around the Sun are dwarfed by the scale of the surrounding Oort cloud.The 52 AU maximum orbit of Pluto and Neptune around the Sun are dwarfed by the scale of the surrounding Oort cloud.

16. Here is a cutaway of an Oort cloud with a radius of ten to the fifth or 100,000 AU. The Oort cloud may account for a significant fraction of the mass of the solar system, perhaps as much or even more than Jupiter. (This is highly speculative, however; we don’t know how many comets there are out there nor how big they are. The very existence of the Oort cloud is only a working hypothesis. Our only evidence is very indirect.)Here is a cutaway of an Oort cloud with a radius of ten to the fifth or 100,000 AU. The Oort cloud may account for a significant fraction of the mass of the solar system, perhaps as much or even more than Jupiter. (This is highly speculative, however; we don’t know how many comets there are out there nor how big they are. The very existence of the Oort cloud is only a working hypothesis. Our only evidence is very indirect.)

17. Much, much closer in, there’s the Kuiper Belt, a disk-shaped region past the orbit of Neptune roughly 30 to 100 AU from the Sun containing many small icy bodies. The Kuiper Belt holds significance for the study of the planetary system on at least two levels. First, it is likely that the Kuiper Belt objects are extremely primitive remnants from the early accretional phases of the solar system. The inner, dense parts of the pre-planetary disk condensed into the major planets, probably within a few millions to tens of millions of years (or even sooner as a report issued just this week claims). The outer parts were less dense, and accretion progressed slowly. Evidently, a great many small objects were formed. Second, it is widely believed that the Kuiper Belt is the source of the short-period comets. It acts as a reservoir for these bodies in the same way that the Oort cloud acts as a reservoir for the long-period comets. So, as a reminder, Mars is 1.5 AU from the Sun, Jupiter is 5 AU from the sun, and Pluto (probably once a Kuiper Belt object) averages around 39 AU from the sun. Comets come from very far away indeed.Much, much closer in, there’s the Kuiper Belt, a disk-shaped region past the orbit of Neptune roughly 30 to 100 AU from the Sun containing many small icy bodies. The Kuiper Belt holds significance for the study of the planetary system on at least two levels. First, it is likely that the Kuiper Belt objects are extremely primitive remnants from the early accretional phases of the solar system. The inner, dense parts of the pre-planetary disk condensed into the major planets, probably within a few millions to tens of millions of years (or even sooner as a report issued just this week claims). The outer parts were less dense, and accretion progressed slowly. Evidently, a great many small objects were formed. Second, it is widely believed that the Kuiper Belt is the source of the short-period comets. It acts as a reservoir for these bodies in the same way that the Oort cloud acts as a reservoir for the long-period comets. So, as a reminder, Mars is 1.5 AU from the Sun, Jupiter is 5 AU from the sun, and Pluto (probably once a Kuiper Belt object) averages around 39 AU from the sun. Comets come from very far away indeed.

18. Stellar Distances So, the solar system may extend out as much as 1.5 – 3.0 light-years from the central sun. And what if that holds true for every single-sun solar system? What is there is almost always an Oort cloud around distant suns? Remember that with stellar distances from our sun it is 4.22 light-years to the current nearest star, Proxima Centauri. If the Oort cloud extends 3 light-years out from our sun then another 1.22 light-years gets you to Proxima Centauri. Does Proxima Centauri have its own version of an Oort cloud and is it possible that Proxima Centauri’s Oort cloud and our sun’s Oort cloud might overlap and interact, perhaps stimulating the bump that sends long-period comets towards both Proxima Centairu as well as on long elliptical tracks around our sun? Even with this three-dimensional representation of the closest stars to the sun, our local stellar neighborhood, you can see that there there is a lot of space in space.So, the solar system may extend out as much as 1.5 – 3.0 light-years from the central sun. And what if that holds true for every single-sun solar system? What is there is almost always an Oort cloud around distant suns? Remember that with stellar distances from our sun it is 4.22 light-years to the current nearest star, Proxima Centauri. If the Oort cloud extends 3 light-years out from our sun then another 1.22 light-years gets you to Proxima Centauri. Does Proxima Centauri have its own version of an Oort cloud and is it possible that Proxima Centauri’s Oort cloud and our sun’s Oort cloud might overlap and interact, perhaps stimulating the bump that sends long-period comets towards both Proxima Centairu as well as on long elliptical tracks around our sun? Even with this three-dimensional representation of the closest stars to the sun, our local stellar neighborhood, you can see that there there is a lot of space in space.

19. And now, on another scale indeed, here is the Milky Way Galaxy viewed from above the galactic plane and just outside the extent of one of its outermost spiral arms. It is a very typical classic grand spiral, one of billions in the universe, nothin particular special in its awesomeness and splendor. We live here.And now, on another scale indeed, here is the Milky Way Galaxy viewed from above the galactic plane and just outside the extent of one of its outermost spiral arms. It is a very typical classic grand spiral, one of billions in the universe, nothin particular special in its awesomeness and splendor. We live here.

20. It is a very nearly symmetrical spiral with a diameter of some 125,000 light-years. If you want miles you can multiply 125,000 times about 6 trillion. It is important to shift gears intellectually now and forget AU altogether. You can’t begin to single out the sun at this immense scale.It is a very nearly symmetrical spiral with a diameter of some 125,000 light-years. If you want miles you can multiply 125,000 times about 6 trillion. It is important to shift gears intellectually now and forget AU altogether. You can’t begin to single out the sun at this immense scale.

21. Remember to allow for the perspective of foreshortening in this picture. A galactic diameter perpendicular to the first diameter also stretches from one side, across the galactic nucleus, to the other side 125,000 light-years away. You should begin to think of the nearly impossible ramifications for intra-galactic space travel, not even mentioning intergalactic space travel, at this point. Remember to allow for the perspective of foreshortening in this picture. A galactic diameter perpendicular to the first diameter also stretches from one side, across the galactic nucleus, to the other side 125,000 light-years away. You should begin to think of the nearly impossible ramifications for intra-galactic space travel, not even mentioning intergalactic space travel, at this point.

22. The hovering point for this artistic rendering of the Milky Way was deliberately chosen by the artists. This painting used to hang down at the Smithsonian Air and Space Museum. It was constructed from then-current knowledge not too may years ago. The vastness of a classic grand spiral is overpowering. I try to remember this painting when I see little slips of faint fuzzy face-on and edge-on galaxies at the telescope. The hovering point for this artistic rendering of the Milky Way was deliberately chosen by the artists. This painting used to hang down at the Smithsonian Air and Space Museum. It was constructed from then-current knowledge not too may years ago. The vastness of a classic grand spiral is overpowering. I try to remember this painting when I see little slips of faint fuzzy face-on and edge-on galaxies at the telescope.

23. Knowing the scale and extent of the galactic diameters in this painting it is possible to make some observations. If you will take the time to consider the data tables for the common stars you ordinarily view you will see that it is a rare star with a listed distance of over 2,000 LY. Practically all of the stars in the Orion OB Association are around 1,600 light-years away. You never get much better than a 3,000-4,000 star night in Maryland and you get no more that 10,000+ stars out in New Mexico. Practically none of these stars that you can see with the naked eye are more distant that 2,000 light-years. The majority are much closer. Knowing the scale and extent of the galactic diameters in this painting it is possible to make some observations. If you will take the time to consider the data tables for the common stars you ordinarily view you will see that it is a rare star with a listed distance of over 2,000 LY. Practically all of the stars in the Orion OB Association are around 1,600 light-years away. You never get much better than a 3,000-4,000 star night in Maryland and you get no more that 10,000+ stars out in New Mexico. Practically none of these stars that you can see with the naked eye are more distant that 2,000 light-years. The majority are much closer.

24. Construct, therefore, a circle on this painting with a radius (not diameter) of 2,000 light-years and you will get circumscribed for you the very paltry portion of stars within the Milky Way that you can see on any given night. I am speaking, of course, of individual stars that resolve to points of light to the naked eye and not the magnificent bands of the Millky Way itself. Our sun is inside that circle that looks like an ellipse due to perspective foreshortening. Every single, individual star you’ve ever seen with the naked eye is inside that circle. True, many favorite deep sky objects lie outside that circle and they are identified on the guide that accompanies this painting. But you should also remember that they are limited to mostly this side of the painting. Our telescopes don’t peer through the arms to see the other side of the Milky Way and they certainly cannot penetrate the galactic core. We see so very little of the Milky Way, in fact, compared to what there may be to see. We have to look away to other galaxies than our own to discern galactic structure and origins. Construct, therefore, a circle on this painting with a radius (not diameter) of 2,000 light-years and you will get circumscribed for you the very paltry portion of stars within the Milky Way that you can see on any given night. I am speaking, of course, of individual stars that resolve to points of light to the naked eye and not the magnificent bands of the Millky Way itself. Our sun is inside that circle that looks like an ellipse due to perspective foreshortening. Every single, individual star you’ve ever seen with the naked eye is inside that circle. True, many favorite deep sky objects lie outside that circle and they are identified on the guide that accompanies this painting. But you should also remember that they are limited to mostly this side of the painting. Our telescopes don’t peer through the arms to see the other side of the Milky Way and they certainly cannot penetrate the galactic core. We see so very little of the Milky Way, in fact, compared to what there may be to see. We have to look away to other galaxies than our own to discern galactic structure and origins.

25. "Space," says Douglas Adams' The Hitchhiker's Guide to the Galaxy, "Is big.  Really big.  You just won't believe how vastly hugely mind-bogglingly big it is.  I mean, you might think it's a long walk down the road to the chemist, but that's just peanuts to space." [Read slide.][Read slide.]

26. The Distance to the Nearest Star The distance from the Sun to Proxima Centauri is 4.22 light years (or 260,000 AU.) So, you can have it both ways if you wish: the distance from the Sun to Proxima Centauri is 4.22 light years which you can multiply by 6 trillion miles per light-year to get just over 25 trillion miles. Or, you can stay with 260,000 AU and know that you would have to go from the earth to the sun more that a quarter of a million times to get out to the next closest star. Either way you’d be right. To be correct, however, you need to remember your units of measure and be able to actively think about what they represent. Once you have a n in-depth understanding of the AU and the light-year you’ll appreciate that size and distance really do matter if you want to understand astronomy better.So, you can have it both ways if you wish: the distance from the Sun to Proxima Centauri is 4.22 light years which you can multiply by 6 trillion miles per light-year to get just over 25 trillion miles. Or, you can stay with 260,000 AU and know that you would have to go from the earth to the sun more that a quarter of a million times to get out to the next closest star. Either way you’d be right. To be correct, however, you need to remember your units of measure and be able to actively think about what they represent. Once you have a n in-depth understanding of the AU and the light-year you’ll appreciate that size and distance really do matter if you want to understand astronomy better.

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