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What else can I help you with?
What are some book titles that begin with the letter A?
Animal DreamsA Prayer for Owen Meany (Does it count if it's just the indefinite article?)Alias GraceAs You Like ItAround the World in Eighty DaysBook Titles Beginning with A: * Are You Ready to Play Outside, Mo Willems * The Absolutely True Dairy of a Part-Time Indian, S. Alexie * All Quiet on the Western Front, E.M. Remarque * Alice in Wonderland, Lewis Carroll * The Adventures of Tom Sawyer, M. Twain * Angela's Airplane, Robert Munsch * Aaron's Hair, Robert Munsch * Alligator Baby, Robert Munsch * Abraham Lincoln, Benjamin Thomas * Are You There God, It's Me, Margaret Judy Blume * The Adventures of Huclkleberry Finn M. Twain * Andrew's Loose Tooth, Robert Munsch * The Adventures of Cellino, B. Cellino * The Alchemist * Around the World In Eighty Days, Jules Verne * The Adventures of Hans Pfall, E.A. Poe * Are You There God, It's Me, Margaret, Judy Blume * Arabian Nights, Anthony Galland
Why does parallel Lines appear to meet in the distance?
If they tend to meet in the distance, the lines have been poorly drawn,or you have to be more accurate when making/constructing them :)=============================No !Parallel lines do appear to meet in the distance. That's the whole basis of theperspective effect in drawing.-- Stand on a railroad track, between the rails, and look at the track-bed in thedistance. The two rails appear to draw together as they get farther from you.-- Same if you stand in the middle of a straight road . . . it appears to get narrowerand the curbs draw together as they get farther from you.-- During a meteor shower, the individual meteors are parallel to each other, butto us, they appear to radiate from a single point in the sky.The reason is how our brains judge linear dimensions ... strictly by the ANGLE thatour eyes measure between two points. Anything that fills a smaller angle is perceivedas being a shorter distance. Distant people and airplanes subtend smaller angles andappear to be smaller than nearby ones, although we learn to compensate for that.The angle that parallel lines subtend at our eyes becomes smaller as they get fartheraway, which our brains interpret as a shorter linear distance between them. Turn itaround, and when you draw a picture of parallel lines, you can make them appear torecede in the distance by drawing them sloped toward each other.
When measuring the distance to a star using brightness shouldn't the calculations take into consideration the effect of the expanding universe and its effect on the apparent brightness?
Not really, and here's why. When we're calculating the distance to a star based on itsspectrum and brightness, we're calculating the distance to a STAR. There are very fewindividual stars that are bright enough to be visible, even in the largest telescopes, inother galaxies. So when we're calculating the distance to a STAR, we're generallylooking at stars in the Milky Way, or perhaps in the Magellanic Clouds. If we're seeingan individual star in a neighboring galaxy, it is generally visible only because it hasgone supernova.Within our galaxy - even within our "local group" of galaxies - we really don't need toworry about the effects of the expanding universe, because the effect is so tiny. Thateffect only manifests itself with the more distant galaxies, and we can calculate thatbased on the red shift of the light emitted by those galaxies.===========================================================================I can't quite pin down in my mind how the expansion of the universe would figure intothe measurement of a star's apparent brightness. But however I try to mash itaround in my mind, I come to the conclusion that it would make no difference.Let's use the round ballpark figure of 2.5 million light years for the distance to theAndromeda galaxy, and let's consider the brightness of a single star in it. (I'm noteven sure that we're able to pick out individual stars that far away, but let's assumethat we can.)Let's also use a current popular estimate of the Hubble constant:65 kilometers per second per megaparsec.Now we come up with something like this:-- Distance to a star in M31 . . . 2.5 million light years = 0.767 megaparsec-- Hubble expansion speed at that distance . . . 0.767 x 65 = 50 km/secondWithout going through the integration, let's just take the quick and dirty assumptionthat it maintains that constant speed away from us during the entire 2.5 million yearsthat it takes the light from that star to reach us.50 km/sec for 2.5 million years would mean that the star is 3.9 x 1015 km farther fromus when we see it than it was when the light left it. That's 0.4 light year ... an increaseof about 0.000016 percent of its distance from us during the time the light was in transit.It would take an increase of about 47 percent to change the apparent brightness byone magnitude, so it seems that the actual change is pretty negligible.And just one more thing . . . The Andromeda galaxy is so close to us that its speedof approach completely masks its Hubble expansion speed, and it's actually movingtoward our galaxy on a collision course.
