Telescopes
Star Characteristics
Star Life Cycles
Star Systems & Galaxies
The Expanding Universe
100
What is electromagnetic radiation? Can we see it? Explain.
Electromagnetic radiation is energy from the sun that can travel in waves through space. We can only see one type of light from the sun - visible light.
100
Name five characteristics that can be used to classify stars, and give three that can be determined using a spectrograph.
Stars can be classified according to color, temperature, size, composition, and brightness. A spectrograph can help determine color, temperature, and composition.
100
What is the star characteristic that determines the life cycle of a star? Is it the same as size? Explain.
The mass of the star determines its life cycle. The mass is how much matter or "stuff" there is in the star. This is not the same thing as size, which more about volume, or how much space something takes up. You can have an object that is very small in size but large in mass and vice versa.
100
Is it common for there to be a single star like we have in our solar system? Explain.
It is not a common situation for stars to exist alone; most stars are members of groups of two or more stars called star systems. Even larger groupings of stars are called clusters (open have less structure and few stars, and globular are larger, densely paced groupings of older stars).
100
How do astronomer's believe the universe began?
Astronomer's believe that the universe was once extremely dense and hot (no larger than the period at the end of a sentence!) and that the universe as we know it formed in an instant when that dense and hot pocket of matter exploded. This is called the Big Bang Theory.
200
What makes each type of electromagnetic energy different from the other types? Do they all reach the Earth? Explain.
There is a whole spectrum of electromagnetic energy, and each type of energy has a different wavelength. Even the different colors of visible light have different wavelengths. Only radio waves, infrared waves, and visible light waves, completely penetrate our atmosphere and reach the Earth's surface.
200
Can you tell the temperature of a star by observing its color? Explain.
If you look at the night sky you can see slight differences int he colors of the stars. The coolest stars are red (with an average surface temperature of 3200 degrees Celsius) and the hottest stars appear bluish (with an average surface temperature of 20,000 degrees Celsius). The sun, a yellow star, has an average surface temperature of about 5,800 degrees Celsius.
200
Do all stars begin in the same way? Explain.
All stars begin their life as part of a nebula (a large cloud of dust and gas). In the densest part of the nebula, gravity pulls the gas and dust together so that they contract into a protostar and become so dense and hot that nuclear fusion starts.
200
What are binary star systems and why do they not always appear to be binary systems?
A binary star system is one in which there are two stars in the system. One star is often much brighter and more massive then the other. Sometimes one periodically blocks the light from the other making it difficult to detect both. This is called an eclipsing binary system.
200
What are some things that provide evidence for the big bang theory? What must be true of a scientific theory?
You must be able to test a scientific theory (able to gather evidence to prove or disprove it). Hubble's Law states that the farther away a falaxy is, the faster it is moving away from us; this strongly support the big bang theory. There is also a glow of widely and evenly distributed radiation called cosmic background radiation which is likely left-over form the big bang.
300
Compare the Spitzer, the Hubble, and the Chandra Space telescopes.
All three of these telescopes are orbiting in space and thus have much clearer images than those telescopes on Earth that might have atmospheric distortions. However, the Hubble is an optical telescope (reflecting) that gathers visible light. The Spitzer telescope produces images in the infrared portion of the electromagnetic spectrum, and the Chandra Observatory produces images in the X-ray portion of the spectrum and is thus capturing images of some of the hottest objects in space.
300
What is another name for the brightness of a star? What factors determine a star's absolute brightness? How does that compare to a star's apparent brightness?
The absolute magnitude (or brightness) of a star is determined by its size and temperature. This is how bright a star actually is, if all stars were a standard distance from Earth. The apparent magnitude is how bright the star is as seen from Earth. This is determined by the absolute brightness and the distance away the star is.
300
What is the difference in the length of the life cycle of a star based on its mass?
Generally, the stars that have less mass us their fuel slowly and can live for a very long time. A star that has more mass will have a shorter lifetime, as it will burn its fuel more quickly. A star that is 15 times as massive as the sun may have only one tenth of one percent the lifetime of the sun.
300
Are the stars in a constellation likely to be part of a star system? Explain.
Ancient observers imagined that groups of stars formed pictures of people or animals (constellations) and used the patterns to located objects in the night sky. Although the stars in a constellation look from Earth as if they might be close together, they generally are not and might not even be part of the same star system. They just happen to lie in the same part of the sky as seen from Earth.
300
How did our solar system form after the big bang?
It is believed that about five billion years ago a giant cloud of gas and dust collapsed to form our solar system. As the center of the nebula became more dense, it shark and began to spin. Eventually the gases became so hot and dense that nuclear fusion occurred and our sun was "born." After that, small asteroid-like bodies called panetesimals which formed the building blocks of the planets, began to collide and clump together forming the planets. Most of the gases near the inner planets burned off due to their proximity to the sun, the outer planets, cooler and farther away, were able to capture and retain many gases.
400
What are the two types of optical telescopes? How do they compare?
The two types of optical telescopes, or telescopes that gather visible light, are refracting and reflecting. A refracting telescope uses convex lenses to gather and focus the light. A reflecting telescope uses mirrors to gather and focus the light. Both use a convex lens on the eyepiece to to magnify the image. The largest optical telescopes are reflecting, because it is easier to make a larger mirror.
400
What is the expected relationship between a star's temperature and it's absolute magnitude? Where on the H-R Diagram would you find the stars that fit this pattern? Are there exceptions? Explain.
The expected relationship between temperature and brightness, is the hotter the star, the brighter it will be. Stars that follow this pattern are found in the main sequence on the H-R Diagram. However, a star's size also affects its absolute magnitude. The larger stars, even if they are cooler, will probably still be very bright (such as red giants), and a smaller, hotter, star still might not be that bright.
400
Will the sun ever supernova? Explain.
The sun is a medium-sized, yellow, dwarf star. It will eventually go through the red giant stage (in which all of the inner planets will be engulfed), and then the outer parts of the star will drift off into space forming nebula that could become new stars. The core of the star that is left behind will cool and become a white dwarf (very dense with no fuel left) that will eventually stop glowing and be characterized as a black dwarf. There will never be a supernova.
400
How do we know dark matter and dark energy exist if we cannot see them?
Scientists use indirect evidence to determine the existence of things that can't study directly. For example, dark matter does not give off electromagnetic radiation and can't be seen directly. But astronomers infer its existence by observing the effect of its gravity on visible objects. After observing that galaxies seem to be moving apart at a faster rate now than they did in the past, astronomers inferred that a mysterious new force called dark energy is causing that acceleration. Current estimates suggest that most of the universe is made not of "empty space," but of dark energy and matter.
500
Observatories are often built on mountains. Why? Why is it even more advantageous to have telescopes in space?
The sky on some mountain tops is clearer than the sky from sea level because it is away from city lights. Also, the atmosphere is thinner and less likely to blur the images. Telescopes in space are outside Earth's atmosphere, so the images won't be distorted at all. Also, the atmosphere won't block any types of radiant energy, so all can types of light can be gathered by a telescope.
500
What is parallax, and how is it used to determine the distance of nearby stars?
Parallax is the apparent change in position of an object when you look at it from different places. Since the Earth is moving, the stars seem to shift positions when we look at them at different times of the year. By drawing imaginary lines to a star at different times of the year, astronomers can find the likely location of the star where the lines intersect. Using some geometry and algebra, they can then determine the distance to the star. This will only work on "nearby" stars, because there won't be much of a parallax for the ones farther away (they will not appear to shift much).
500
How do the events in the life cycle of a massive star compare to those of a lower mass star?
A lower mass star never supernovas. After the red giant stage, it will slowly die out becoming first a white dwarf and the a black dwarf. A massive star will experience the red giant stage more dramatically (it will become a super giant), and then it will supernova (explode) forming either a neutron star (which lasts forever) or, if it is an extremely massive star, a black hole (which also lasts forever and has so much gravity that not even light can escape.
500
What is the largest grouping of stars and how do the types compare with each other?
The largest grouping of stars, a galaxy, which includes single stars as well as star systems and clusters, can be classified as either spiral, elliptical, or irregular. Elliptical galaxies, which look like round or flattened ball, contain billions of stars but have very little gas and dust between them, and so are likely to have only old stars and no new stars forming. Spiral galaxies (in the shape of a pinwheel) have very few stars forming in the dense center; new stars are found in the spiral arms where there is more room for gas and dust. Irregular galaxies, with no particular shape, are typically smaller and have more new stars due to a larger amount of room for gas and dust.
500
What are the two possible futures of the universe?
One possibility is that the universe will continue to expand as it is doing now, and all of the stars will eventually run out of fuel and burn out, leaving a cold and dark universe. Another possibility is that the force of gravity will begin to pull the galaxies back together resulting in a reverse of the big bang - a big crunch in which all of the matter of the universe would be crushed into an enormous black hole. However, new observations of the phenomena of dark energy, the force believed to be accelerating galaxies away from each more and more rapidly, suggests that the first possibility is the most likely.
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