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Definition
| The Theory that all planets form within a disc, a large cloud of gas begins to collapse under it’s own gravity to form Sun and Planets |
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| Irregularities from Nebular Theory |
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Definition
| the spirals in the milky way do not follow the Nebular theory. because of Differential rotation which is the difference in the angular speeds of different parts of the galactic disk so stars closer to the center complete a greater fraction of their orbit in a given time. But differential rotation is too efficient in making the spiral arms. After only 500 million years, the arms should be so wound up that the structure disappears. Also, the spiral pattern should occupy only a small part of the disk. The observations of other galaxies contradicts this: the spiral arms in spiral galaxies rarely have more than two turns.
if nebula Theory was correct then the milky way should have many more spirals
one major flaw is that it can't explain large planets near the star. I.E: it has a very difficult time explaining why Uranus and Neptune are so small.
Also that some planets spin backwards |
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- Radio Telescopes
- infrared (heat sensing)
UV Telescopes
X-Ray Telescopes
Gamma Ray Telescopes |
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Definition
Refractors: bending of a light beam as it passes from one transparent medium
- refracting telescope uses a convex len.
- Reflection: perfered optical telescope type. uses curved mirrors in back of telescope to reflect light in to and eye piece. light touches nothing but air
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- X-Ray
- Gamma Ray
- Radio Astronomy
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Term
Milky Way
Structure / Type |
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Definition
- barred Spiral Galaxy, eliptical center,
- The stellar disk of the Milky Way galaxy is approximately 100,000 light-years (9.5×1017 km) in diameter, and is believed to be, on average, about 1,000 ly (9.5×1015 km) thick.[7] It is estimated to contain at least 200 billion stars[8] and possibly up to 400 billion stars,
- the Milky Way classafication on The Hubble Galaxy Classification Scheme is SBa, which is a barred spiral with a eliptical center
- Our galaxy, the Milky Way, is disk-shaped with spiral arms in the disk. It has an elliptical bulge in the center with a bar-shaped distribution of gas/dust/stars going through the middle out of which the spiral arms extend and a spherical halo of stars that is denser closer to the Galaxy center
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Definition
- 95% of the Milky Ways mass is dark matter
- we can only see 5% of its contents
- in that 5% we see dust, gases, and stars
- sections of milky way:
- contains the oldest stars in the Galaxy
- The Halo consists of the oldest stars known, including about 146 Globular Clusters, believed to have been formed during the early formation of the Galaxy with ages of 10-15 billion years from their H-R Diagrams. The halo is also filled with a very diffuse, hot, highly-ionized gas. The very hot gas in the halo produces a gamma-ray halo.
- The nuclear bulge and Galactic Center.
- The disk, which contains the majority of the stars, including the sun, and virtually all of the gas and dust
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The disk of the Galaxy is a flattened, rotating system which contains the Sun and other intermediate-to-young stars. The sun sits about 2/3 of the way from the center to the edge of the disk (about 25,000l.y. by the most modern estimates). The sun revolves around the center of the galaxy about once every 250 million years. The disk also the galaxy about contains atomic (HI) and molecular (H2) gas and dust.
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Definition
- The galaxy rotates about its center according to its galaxy rotation curve The discrepancy between the observed curve (relatively flat) and the curve based upon the known mass of the stars and gas in the Milk Way (decaying curve) is attributed to dark matter.
- Differential rotation; things in the center complete there rotation faster the then thing out further towards edge of he galaxy
- Rotates once ever 240 million years, learned through dopler shift.
- To determine the rotation rate of the Milky Way, astronomers mapped star forming regions using the Very Long Baseline Array (VLBA) radio telescope. The molecules in these regions amplify naturally occurring radio emissions. By observing how far these regions shifted over time in three dimensions, they were able to calculate the rotation of the entire galactic disk
- Our galaxy, the Milky Way, has about 3 billion solar masses of H I gas with about 70% of it further out in the Galaxy than the Sun. Most of the H I gas is in disk component of our galaxy and is located within 720 light years from the midplane of the disk. What's very nice is that 21-cm line radiation is not blocked by dust! The 21-cm line radiation provides the best way to map the structure of the Galaxy.
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Definition
- February 11th 1800. Herschel was testing filters for the sun so he could observe sun spots. When using a red filter he found there was a lot of heat produced. Herschel discovered infrared radiation by passing sunlight through a prism and holding a thermometer just beyond the red end of the visible spectrum. This thermometer was meant to be a control to measure the ambient air temperature in the room. He was shocked when it showed a higher temperature than the visible spectrum. Further experimentation led to Herschel's conclusion that there must be an invisible form of light beyond the visible spectrum.
- Realized we were in the middle of a Grindstone.
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Definition
used the period-luminosity relation for Cepheid variable stars to determine distances to globular clusters.
He was the first to realize that the Milky Way Galaxy was much larger than previously believed, and that the Sun's place in the galaxy was in a nondescript location.
found out we are NOT at the center because galaxy is asymeterc
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Term
| Population I / Population II |
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Definition
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Population I -
- Open Clusters | Young | Blue | 3% Hydrogen | found in disc
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Population II
- Globular Clusters | Old | Red | No metals | found in halo
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Definition
| galaxies are in constant interaction with each other and that the biggest ones get bigger by engulfing smaller ones. |
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Definition
| About 99% of the interstellar medium is gas with about 90% of it in the form of hydrogen (atomic or molecular form), 10% helium, and traces of other elements. At visible wavelengths, however, dust has a greater effect on the light than the gas. The presence of interstellar gas can be seen when you look at the spectral lines of a binary star system. Among the broad lines that shift as the two stars orbit each other, you see narrow lines that do not move. The narrow lines are from much colder gas in the interstellar medium between us and the binary system. |
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Definition
Emission nebulae, or nebulae that glow with their own light, exist where relatively dense interstellar material is found in the vicinity of hot stars. Such material may be left over from star formation or from stellar mass loss in supernovae, planetary nebulae, or novae. Ultraviolet light from the hot stars is absorbed by the gas, ionizing the hydrogen (also termed HII, hence the alternative name HII regions) at a high temperature, around 10,000 K. As ionized hydrogen recombines with electrons, hydrogen emission lines in the visible part of the spectrum are produced.
2.
1. if the nebula is reddish in color it's hydrogen
2. if it is greenish in color its oxygen
3. place where stars are born
also known as HII Region |
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Term
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Definition
1. If no hot stars are present, the interstellar gas will be cold, and dust may condense from the heavier elements. Interstellar dust has a size and structure similar to soot particles, and in the densest regions the dust may completely obscure the light of stars behind it, producing an absorption nebula, or dark nebula. Typical dust cloud sizes are about 10 pc, with representative masses of about 50 solar masses.
1. absorbs light
2. denise cloud of dust
3. no light can get through
4. opaque because of their internal dust grains.
5. The form of such dark clouds is very irregular: they have no clearly defined outer boundaries and sometimes take on convoluted serpentine shapes. |
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Definition
| The obscuring effect of dust is primarily the result of scattering or reflecting light into different directions. A dust cloud near stars but not close enough to destroy the dust through heat or ultraviolet radiation will preferentially reflect the stars' blue light; hence a bluish-looking nebula can be observed |
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Term
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Definition
| An H I region is an interstellar cloud composed of neutral atomic hydrogen (H I). These regions are non-luminous, save for emission of the 21-cm (1,420 MHz) region spectral line. This line has a very low transition probability, so requires large amounts of hydrogen gas for it to be seen. At ionization fronts, where H I regions collide with expanding ionized gas (such as an H II region), the latter glows brighter than it otherwise would. Most of the matter between the stars in the Milky Way Galaxy, occurs in the form of relatively cold, neutral hydrogen gas with a temperature of only about 100 K and a density of approximately one atom per cubic cm. There also exist cold compact hydrogen clouds with a density of at least 10 particles per cubic cm. Hydrogen clouds are easily detectable at radio wavelengths because they emit a characteristic energy at a wavelength of 21 cm |
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Definition
| H II regions are regions of hot ionized, thin hydrogen emission nebulae that glow from the fluorescence of hydrogen atoms. |
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Definition
1. Wavelength of Hydrogen
2. measured with radio telescopes
3. The energy state of an electron spinning anti-parallel is slightly lower than the energy state of a parallel-spin electron. Remember that the atom always wants to be in the lowest energy state possible, so the electron will eventually flip to the anti-parallel spin direction if it was somehow knocked to the parallel spin direction. this releases a proton that can be detected at The wavelength of 21.1 centimeters |
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