Universe the milky way galaxy worksheet answers

Continue \(\def\| {&}\DeclareMathOperator{\D}{\\bigtriangleup\!} \DeclareMathOperator{\d}{\\text{d}\!} \) This page answers questions about galaxies and the Milky Way. The questions are: [248] [323] 1. Galaxies Galaxies are clouds of stars with millions or billions of stars and often also with gas clouds and so-called dark matter. There are countless other galaxies beyond those of our own. You can see the nearest one with your own eyes, without using a telescope. These are the Small Magellanic Cloud (in the constellation Tucana - the Toucan), the Large Magellanic Cloud (in the constellation Dorado - the Goldfish), and the Andromeda (in the constellation Andromeda). Just as our Milky Way consists of stars and other things with a lot of empty space in between, so the universe consists of galaxies with a lot of empty space in between. Many of the Messier objects are galaxies, for example M 31 (the Andromeda Nebula). You list them (with links to photos) on //www.seds.org/messier/objects.html#galaxy. Galaxies come in many shapes and sizes. Edwin Hubble devised the classification scheme that is still used today to indicate the type of galaxy. In Hubble's diagram, there are four main types of galaxies: elliptical galaxies (indicated by the letter E), spiral galaxies (S), barred spiral galaxies (SB) and irregular galaxies (Irr). Elliptical galaxies are shaped like a rugby ball and look like an ellipse or circle from all sides. They usually contain no gas and no internal structure. The largest galaxies are elliptical galaxies. Type E is divided into subclasses indicated by a number. The smaller the number, the flatter the galaxy. E0 is plattest, and E9 the most spherical. Spiral galaxies look like a flat disc and have spiral arms that swing their way from the center to the edge of the disc. Spiral galaxies contain many gas clouds and stars. The subclasses of type S and Sa, Sb and Sc. Subtype a has tightly injured spiral arms and a relatively large core. Direction subtype c, the arms become less tightly wrapped and the core becomes smaller. If a galaxy is located between, say, Sb and Sc, it is sometimes classified as Sbc. Barred spiral galaxies are like spiral galaxies, but have a kind of beam that runs through the center. Spiral arms often sprout from the ends of the bar. Barred spiral galaxies have the same subtypes a, b and c as ordinary spiral galaxies. Irregular galaxies do not fit into any of the other classes and, as their name suggests, have an irregular shape. Many small galaxies are irregular galaxies. [92] The difference between, for example, type SBa and type Sc is that SBa is a barred spiral and an ordinary spiral is, that SBa has tighter injured spiral arms and a more prominent core than Sc. [14] 2. The Milky Way The Milky Way is the galaxy to which the sun belongs. The Milky Way looks a band of faintly shining clouds in the sky, which are always in the same place between the stars, and thus move with the stars along the sky. You can only see the Milky Way from dark places far from the light of cities. From the Netherlands it is difficult to see the Milky Way, because almost everywhere there are one or two cities nearby that cause light pollution. The best time to see the Milky Way is when it crosses the sky straight at midnight. The time of year in which this happens depends on your latitude, but it is about early January and early July. The Milky Way passes through the following known constellations (and by others too): the Swan, Cassiopeia, the Centaur, the Scorpio, the Sagittarius. [598] 3. Milky Way and Galaxy The Galaxy is the same as one of the meanings of the Milky Way, namely the total of all gas clouds and stars, including the sun, which are bound together by gravity and move through the universe together, separated from other similar galaxies. That meaning is quite young and dates to about 1930. The other - much older - meaning of Milky Way is the faintly shiny band in the air. That significance dates back more than 2,000 years. At that time, people didn't know that that band consists of the light of countless stars that are too faint to see with the naked eye, so it made sense to think of the Milky Way and the stars as two completely separate things. It became clear that this faintly shiny band consists of countless stars only after the invention of the telescope around 1608. And that the Milky Way doesn't fill the entire universe, but that there are more galaxies like ours, and that we therefore need a word for something like this, has only been known since about 1930. So the confusion that can arise between Milky Way as the name for only the faintly shiny band in the sky, and Milky Way as the name for the entire galaxy is due to the meaning of Milky Way having expanded over time, when the nature of the Milky Way became clear. [481] 4. The central line of the Milky Way The central line of the Milky Way is the equator of the galactic coordinate system as defined by the IAU. For example, this coordinate system is described on //en.wikipedia.org/wiki/Galactic_coordinates#In_terms_of_equatorial_coordinates. The equatorial coordinates of the galactic equator referred to the standard equinox of B1950.0 can be found on the basis of the following formulas (based on chapter 12 of [Meeus]: \beginning{align} \tan y \| = \frac{\tan(l - 123°)}{sin (27.24°)} \\ α \| = y + 12.25° \\ \sin δ \| = \cos(27.4°) \cos(l - 123°) \end{align} In these formulas, \(α\) is the correct ascension, \(δ\) declination, and \(l\) galactic length. These formulas are part of the definition of the galactic coordinate system, so they are precise. however, steratlass are referred to the standard equinox of J2000.0 instead of that of B1950.0, so you need to correct for the precession between 1950 and 2000 if you want to know the coordinates of the galactic equator compared to J2000.0. There seem to be quite a few websites that discuss or at least call these coordinates transformation. Type galactic coordinates 192.25 into your favorite search engine to find a few. Note: Before 1959, an older galactic coordinate system was used, which had a slightly different equator. I found several references (such as the Wikipedia article) that confirm that it was the IAU that defined this new galactic coordinate system, but I haven't found the exact IAU publication it contains. Many IAU publications are not freely available to the general public. [238] The Milky Way is what we can see from the galaxy in which we find ourselves, which is also called the Milky Way or Milky Way. Our Galaxy has a diameter of about 100,000 light years. The center of the Milky Way lies in the direction of the constellation archer (Sagittarius) at a distance of about 25,000 light years from the sun, but is hidden from our view by thick clouds of gas and dust. The sun takes about 200 million years to orbit the center of the Milky Way. [337] 5. The plane of the Milky Way Galaxy is shaped like a thick disk of stars and clouds of gas, and we are in that disk. The plane of the Milky Way is a plane that divides the disk of the Milky Way into a lower part and an upper part (as if you were cutting a pancake so that you get two pancakes that are half as thick). An equator is usually a flat boundary of zero thickness that divides an object into two parts that are equal in some natural sense. The milky way's disk is slightly contorted, so the vertical center creates a surface that is also slightly contorted. For convenience, we call that surface the equator of the Milky Way, but it's not perfectly flat. The Sun is currently a few dozen light years north of that plane, but it's not entirely clear how many, exactly, which means not everyone agrees where the Milky Way's plane runs near the sun. That's not very surprising, because the plane of the Milky Way is not marked in space by strange stars or anything like that. Finding the plane of the Milky Way is similar to finding the midline of a long but narrow forest without sharp edges. Most people will agree on about where the centerline is, but where exactly it is is not so clear. Some people say that the sun is now 20 light years north of the Milky Way plane, others say 45 light years, and //www.ingenta.com/isis/searching/Expand/ingenta?pub=infobike://klu/astr/2003/00000288/0000004/05123578 says 34.6 The sun wobbles around the plane of the Milky Way and passes through the plane about every 35 million years or so. [519] Gamma rays are his extremely hot or otherwise extremely energetic materials, and also during certain radioactive processes where one type of matter is changed to another. So, if there is little matter in some regions, then you can't expect many gamma rays from that region. The highest densities of material in the Milky Way are found in the milky way's disk, so it is to be expected that more gamma rays come from the milky way's disk than from regions outside the disk. The density gradually decreases over a few hundred light years when you move vertically from the vertical middle of the disc, so I expect that gamma ray emissions will also gradually decrease over such distances above or below the equator. An equator is not a separate object and can (almost) never be easily detected from natural evidence in the area around the equator. For example, you don't see in an image of a particular area near the equator on Earth exactly where the equator is running. The area appears on both sides of the equator, and does not suddenly change when you cross the equator. Similarly, it's not easy to tell exactly where the equator of the Milky Way is, and there is no sudden increase or decrease in gamma ray emissions or reception when you cross that equator. As far as we know, the sun is always in the disk of the Milky Way, and has crossed the equator many times in the past, so any sudden increase or decrease in the reception of gamma rays should be related to specific gamma ray sources, rather than to the exact location of the sun relative to the equator of the Milky Way. [339] 6. The Milky Way Galaxy is a Spiral Galaxy The Milky Way galaxy is a spiral galaxy. That means that the milky way's flat disk contains a number of arms that make their way from the center to the edge. You take a picture of the structure of the Milky Way (as discovered so far) on //www.ras.ucalgary.ca/CGPS/where/plan/. If you start in the middle and move outwards along the sun, you will come across the following arms: the Norma arm, the Scutum-Crux Arm, the Sagittarius arm, the local arm and the Perseus Arm. There is also a piece of arm called the Outer Arm, but that seems to be part of the Norma Arm. These arms (with the exception of the local and outer arms) are named after the constellations they contain (as seen from Earth). The local arm in which the sun happens to be in is not a full arm. At the end of 2003, Australian astronomers from CSIRO (//www.atnf.csiro.au/news/press/spiralarm/) reported that they discovered a new piece of spiral arm at 15 - 20 kpc from the middle. It is quite possible that this is yet another part of the Norma Arm, at even greater distance from the center than the Outer Arm, which also appears to be part of the Norma Arm. [110] 7. The name of the Ancient Greek astronomers thought the Milky Way looked like a river of milk milk through the sky, and that's where both Milky Way and Galaxy come from. Galaxy comes from the Greek word for milk. [13] 8. The discovery of the Milky Way A very long time ago there were no cities, and no city lights. The people of that time could even see very dim stars and the Milky Way every cloudless night. So it's likely that humans have been aware of the Milky Way for thousands of years, and we can't say who first discovered the Milky Way. However, it took us a long time to discover the true nature of the Milky Way. After the invention of the telescope in 1609, people saw that the Milky Way contained many seemingly faint stars that could not be seen individually without a telescope. In 1755, the philosopher Immanuel Kant suggested that some nebulae visible in the sky could be distantly separated Galaxies, rather than small nebulae within one giant Milky Way that filled the entire universe. It wasn't until 1923 that Edwin Hubble (for whom the Hubble Space Telescope is called) proved that some of these nebulae are indeed far beyond our own Milky Way galaxy, and that our Milky Way does not fill the entire universe. Today, we know that our Milky Way is just a typical spiral galaxy, in the backwater of the universe. [121] 9. The discovery of the center of the Milky Way The discovery of the center of the Milky Way was a lengthy process involving many people. Until the beginning of the 20th century, we didn't know where the center of the Milky Way is. Many people believed then that the Milky Way filled the entire universe; At least, no one had proven otherwise. However, there were indications that the Milky Way was not the same in all directions. The observations of nebulae collected by J. Herschel (1864) and Mr. Dreyer (1888) showed that spherical clusters have a great preference for the side of the sky where the constellation of the Sagittarius is. Moreover, the Milky Way does not seem equally bright in all directions. It is brightest near the constellation of the Sagittarius, and least bright near the constellation Perseus. This was particularly evident in O. Boeddicker in Ireland (1892) and C. Easton in Dordrecht (1893). In 1922, Freundlich and Von der Pahlen discovered that stars of spectral type B showed a remarkable distribution of speed that depended on their position along the Milky Way. In 1927, J.H. Oort from Leiden in the Netherlands showed that this remarkable distribution could be explained if you assumed that the Milky Way revolves around a center that was about 6000 pc away towards the constellation of the Sagittarius. (I summed up a lot of this history of [Pancake].) Nowadays, with many more measurements of different species, astronomers think the center is more like 8000 pc away. All the gas and dust between us and the center of the absorbs so much of the light that we see all the way to the middle on ordinary photos. (The total absorption is about 27 larges!) Radio waves, infrared radiation and gamma rays suffer much less from such absorption, so we can record this kind of radiation from the center, but only since about the fifties (radio) and the eighties (infrared, gamma). Around 1990 it became clear that the compact radio source Sagittarius A* (often abbreviated to Sgr A*) is located in the exact center of the Milky Way and is associated with a black hole of 3.6 million solar masses. That radio source was discovered in February 1974 by Bruce Balick and Robert Brown. The name Sagittarius A* was first used by Robert Brown in 1982 and has since become the default name for that object (according to [Goss]). [73] 10. The direction of the center of the Milky Way The center of the Milky Way (between the constellations of the Sagittarius, the Scorpio, and the Snake Bearer) is about 5 degrees in the sky from the path that takes the sun (the ecliptic), so the sun is always at least 5 degrees away from the center of the Milky Way, and the line through the Earth's space through the sun to the center of the Milky Way always has a curve of at least 5 degrees in. [191] The equatorial coordinates of the direction to the center of the Milky Way Galaxy are (relative to the equinox of 2000.0): correct ascension 17h46m, declination −28°56'. Things that do not move relative to the stars (such as the stars themselves) always rise at the same sideways time and always at the same sidereal time, as seen from a fixed location. For the center of the Milky Way, those sideways times are listed in the following table, in the Rise and Set columns. Latitude Rise Set Straight Overhead 90° north never 80° north never 60° north 16:39 18:53 02:41 23:01 50° north 14:31 21:01 04:20 21:22 4 °30° north 21:20 13:37 21:55 05:09 20:33 30° north 13:00 22:32 05:42 20:00 20° north 12:32 23:00 06:08 19:34 10 ° 12:08 23:24 06:30 19:12 11:46 23:46 06:51 18:51 10° south 11:24 00:08 07:12 18:30 20 ° south 11:00 00:32 07:34 18:08 30° south 10:32 01:00 08:00 17:42 40° south 09:55 01:37 08:33 17:09 50° south 09:01 02:31 09:22 16:20 60° south 06:53 3 04:39 11:01 14:41 70° south always never 80° south always never 90° south always never Never The transformation of sidereal time to clock time is explained on the Page of the Time. 11. The Mily Way Straight Over Your Head When the Milky Way goes right over your head, the midline of the Milky Way makes a right angle with the poles of the Milky Way, so those poles should be on the horizon. The North Pole of the Milky Way has right ascension 12h51m and declination +27°08' (compared to the equinox J2000.0). That point is on the horizon on the two sidereal times included in the previous table in the Straight column 12. The Neighbors of the Milky Way Our Milky Way Is part of a group of galaxies called the Local Group. The nearest neighboring galaxy about the size of our own Milky Way is the AnromedAnevel (M 31). The Galaxy also has some smaller neighbors, all of which probably haven't all been discovered yet. The most famous small neighbours are the Large Magellanic Cloud and the Small Magellanic Cloud. You can find a list on the UniverseFamilyTree Page about clusters of galaxies. [12] 13. Thousands of millions of galaxies If we assume that the universe looks pretty much the same everywhere (against which we have no clues), then there must be thousands of millions of galaxies in the universe. A typical galaxy has a mass of about 100 thousand thousand times that of the Sun (measured from the movements in and around the galaxy, which depend on all mass, including invisible mass). If we divide the total mass of the visible universe (about 4 × 1022 solar masses or 9 × 1052 kilograms) by the typical mass of a galaxy, we get an estimate of about 400 million galaxies in the visible universe. Only a very small proportion of all those galaxies have been studied. Even the Sloan Digital Sky Survey (www.sdss.org), the largest systematic census of objects in the universe, has only about 100 million objects, including an estimated one million galaxies. [428] 14. Active galaxies The leading models for active galaxies assume that there is a large black hole at the center of such a galaxy and that a large amount of energy is released by material from the environment that falls into the black hole. See //en.wikipedia.org/wiki/Active_galaxy and //imagine.gsfc.nasa.gov/docs/science/know_l1/active_galaxies.html. See //www.ast.man.ac.uk/~rb/agn/ for the Active Galaxies Newsletter. [284] 15. The Great Wall There are many very large concentrations of galaxies. One, about 300 million to 500 million light years from Earth toward the constellations of at least Leo to Herculus, is known as the Great Wall. However, its full extent is not yet known, and it is not everywhere very well separated from neighboring concentrations of galaxies. The part we've seen so far measures about 200 by 600 by 20 million light-years in size. See //www.angelfire.com/id/jsredshift/grtwall.htm and //adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1992ApJ... 384.396R. [365] 16. Lonely Galaxies The galaxies in the universe are so far apart because they formed from much larger clouds of gas and dust that collapsed and shrunk due to their own gravity. All the gas and dust from a very large area of space concentrated in a single galaxy that is only a very small part the region of space filled so that the rest of the space ended up empty. If each galaxy ended up where the center of the cloud used to be, and as two of clouds hit each other, then the distance between the two galaxies that formed from them would still be many times greater, because those galaxies are so much smaller than the original clouds. The universe is also expanding, so galaxies are now farther apart than thousands of millions of years ago. The space between galaxies is usually empty. There may be a few stars that have escaped from a galaxy, and there are a few protons and electrons here and there, but all in all there is so little matter that a similar situation in a laboratory on Earth would be called a good vacuum. [291] 17. Colliding galaxies Galaxies are usually millions of light years apart, yet there are occasional collisions between galaxies. A galaxy is usually empty space, so it is very unlikely that stars of both galaxies will collide. What exactly happens, when two particular galaxies collide, depends on the mass of the galaxies, on the smallest distance between them during the collision, on the relative speed and on the orientation of the galaxies. It may be that the two galaxies will merge into a single galaxy, but it may also be that they have only a slight change of direction. It may be that one of the galaxies loses stars to the other, or that both stars lose to each other. Often tidal forces cause large groups of stars to be ejected into the universe, and these form (temporary) tails to the galaxies. It also often happens that the collision generates a pressure wave that passes through the galaxies and causes star formation. Such a galaxy will contain unusually many young, bright stars for a few million years. [442] 18. How to tell if a Point of Light is a Galaxy or a Star One can identify the nature of a point of light by its spectrum and brightness. The spectrum of a galaxy is the combination of the spectra of all its bright components, usually the stars, but sometimes also with a large contribution of an Active Galactic Nucleus (AGN, for example in quasars). The spectrum of an AGN looks very different from that of a star, so the difference is pretty easy to spot when you measure the spectrum. Because the spectrum of a normal galaxy (without agn) is the combination of the spectra of stars of many different species, it usually does not exactly resemble the spectrum of a particular type of star, and from this you can see that it is not the spectrum of a single star. A galaxy is much larger than a single star, so a galaxy must appear very far away indeed in the sky as just a point of light. At such great distances, the galaxy is likely to have a large of its spectrum (due to Hubble's law and the expansion of the universe), which means that all spectral lines are shifted to longer wavelengths compared to the same spectral lines in the spectrum of a nearby star. The redshift gives the and the distance along with the apparent brightness indicates how much light the object emits, which is much greater for a galaxy than for a single star. A small object in our solar system appears as a point of light in our sky, and such an object can be told apart from a star or galaxy by its spectrum, for example because the spectrum reveals the temperature of the object, and objects in our solar system (other than the sun itself) are much cooler than the sun and other stars are. Such objects also reflect sunlight, which bears the temperature signature of the sun, so one should be careful to check for another contribution from the object itself, with a much lower temperature. [590] 19. Moving galaxies We have direct and circumstantial evidence that galaxies are moving. Circumstantial evidence is that many galaxies look like they've been disturbed by the severity of something else, and that must have been something with a similar amount of mass, and other galaxies are good candidates for that. Sometimes such a different galaxy is close to the disrupted galaxy, but sometimes there is no other galaxy around, and then that galaxy must have been closer in the past than it is now, so it must have moved. The direct evidence is the Doppler shifting the spectral lines into the light emanating from those galaxies. Just as the pitch of a siren increases when the ambulance drives towards you, and decreases when the ambulance drives away from you, the frequency of light waves also increases or decreases as the source of the light comes towards or away from you. The light coming from galaxies has many spectral lines that we know what their real frequencies are, so we can determine their speed along the line of sight. Determining the speed of galaxies perpendicular to the line of sight (i.e. across the sky) is a lot more difficult than determining the speed along the line of sight. Of most galaxies whose speed we know along the line of sight, we don't know their speed on the other side of the sky. We don't have a preferred position in the universe, so the spread of galaxies around the local average is about as wide on the line of sight as along the line of sight. The typical speed of a galaxy relative to its neighbors is in the order of 10 to 100 km/s. languages: [en] //aa.quae.nl/en/antwoorden/melkwegstelsels.html; Last updated: 2020-07-18 2020-07-18

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