What is a parsec and why is it necesssary when a "lightyear" would do just fine to measure distance?

Answer 1

A parsec is the unit most astronomers use. A parsec is 3.26 light years, and the reason astronomers use it is because it is easier to convert to when measuring closer stars. That is because if a star was exactly one parsec away, the paralax angle it would form over the course of a year would be exactly one arcsecond.

Translating that into english, imagine a 360 degree circle. Now, divide each of those degrees into 60 parts. Now divide each of those 60 parts into 60 more parts. That reeeeeeeally tiny angle is one arcsecond. Because the Earth circles around the sun, it moves in relation to other stars in the galaxy, and it forms a paralax.

Here's an example of paralax: Close one of your eyes, hold your thumb out at arm's length, and cover something up with it. Then, switch eyes, and your thumb won't be covering the same thing anymore. The same thing happens on a much larger scale in space. The earth, over the course of 6 months, travels the diameter of its orbit to the other side of the sun. The background of stars shifts during that time because we are at a slightly different angle than before.

If a star was 3.26 light years away, this star would shift by exactly one arcsecond, or 1/3600 of one degree on the sky. Because this is the primary method of determining distances of stars closer to earth, it is a convenient unit to use.

That being said, the light-year is much easier to understand.

Answer 2

A parsec is the distance, approximately 3 1/4 light years, at which the PARallax of a star is equal to one SECond of arc.

When the earth moves, in six months' time, from one side of its orbit to the other, it is about 180 million miles from where it started. The position of a nearby star compared to the background of more distant stars will be very slightly different when seen from one location in the Earth's orbit than the opposite location.

You can demonstrate the effect for yourself by holding your thumb out at arm's length, and using your free hand to cover first one eye, then the other. Your thumb, representing the nearby star, will appear to move relative to the wall (or whatever) in front of you, which represents the distant star. The closer you hold your thumb to your face, the more pronounced the difference becomes.

Distances in space, however, are so vast that the nearest star to the sun, Alpha Centauri, has a parallax of only about 3/4 seconds of arc. One second of arc is 1/3600 of a degree (60 minutes to the degree, 60 seconds to the minute.) Therefore, that star is a little over 4 light years (roughly 1 1/3 parsec) away.

More distant stars have even smaller parsecs, and after awhile they become so small as to be immesurable. Then we must use other methods, such as measuring red shift, to determine the distance to a star.

Use of the parsec, as opposed to the light year, makes certain calcuations easier by eliminating some of the need to convert units of measurement.

Answer 3

Builders often measure things by using angles, say 145 degrees, 90degrees, 60degrees, 45degrees. Connecting such angles by a third long line, you get "fat" triangles. Sometimes small angles are used... 10 degrees, 5degrees, 1degree. Connecting such angles by a third short line, you get "skinny triangles". Using trigonometry, you can use an angle & one of the line lengths to figure out the length of the other lines mathematically...& it will be correct. The calculated length of the third line will be the same as the line length if you measure it! Its kinda fun to do. In the 1800's astronomers got a really neat idea to measure distance to a star. The earth moves around the sun in a nearly circular orbit. The rough diameter of the near circle around the sun is about 185million miles! That could be one of the lines of a triangle. If they could get a measurement of any shift angle of a "nearby" star as viewed from two points opposite each other across the orbit of the earth around the sun, they could calculate the distance to that star! This was very difficult since no star other than the sun is nearby. Therefore no star they measured ever had a shift angle they could measure. Finally, a sun was found that had a shift angle. But this angle was not measured in degrees. It wasn't even measured in 1/60th of degrees which are called minutes! If the star could have been measured in 1/60th of 1/60th of degrees which are called seconds, such a long long long skinny triangle(with the short line being 185 million miles long) would have had a distance of one of the long legs of 5.87 million million miles or 1 parsec or 3.26 lightyears distance! ..... but the distance wasn't even that close! 61 Cygni had a measured angle of 0.3 of 1/60th of 1/60th of a degree placing the star over 11light years away & placing the measurement itself as one of science measurements greatest achievements! Such a long long long long skinny triangle & so far away! The universe lept to an unimaginable size. Yes, the universe has taken many leaps in size as scientists learned more, but this was the first really really huge leap....in conjunction with the reality of the parsec. You must forgive professional astronomers if they measure distances in parsecs(& now megaparsecs-millions of parsecs). Professional astronomers have the right to measure in parsecs & megaparsecs.

Answer 4

A parsec is the distance of an object that has a heliocentric parallax of one arc second. What is more, the inverse of the parallax equals the distance in parsecs. So if the star has a parallax of 1/10 arc second, then the distance is 10 parsecs. If another star has a parallax of 0.0132 arc seconds, its distance is 1/0.0132 parsecs (about 76 parsecs). Since the parallax is directly measured at the telescope, using parsecs simplifies distance calculations.

Answer 5

a parsec is 3.08568025 × 10^16 meters

1 lightyear = 9.4605284 × 10^15 meters

a parsec = 3.26163626336 lightyears

Answer 6

It is a paralllax second of arc. The parallax of a star is half of the angular distance a star appears to move against the celestial sphere due to the orbit of the Earth around the Sun. It is equal to 3.2+lightyears. It is used because one can measure the angle of the star at two opposite sides of the earths orbit around the sun

Answer 7

i have no idea about a parsec before. but i understand why a lightyear would do just fine to measure distance.this is because the speed of light is always constant. we can get know the distance by measure the time which taken by light go through,then using the formula:time*the speed of light.haha, actually i dont know about anything.just try to answer for fun

Answer 8

A 'Parsec' is a measurement of stellar distances.
It represents 3.261 light-years.

The nearest star to us, (other than our sun), is Proxima Centauri and is 1.29 parsecs away.

1 light-year is represented by the distance light travels in 1 year at a speed of 186,000 miles per second. (1 mile = 1.6 km)

The mind boggles doesn't it?

Answer 9

"Allowing the cultural center/mosque to be built near the site of 911 is not a sign of weakness, but a sign of strength. It shows intelligence that we can separate in our minds the muslims that are peaceful from the violent extremists" I've been saying that all along. It's a sad commentary though on how Americans perceive Islam when a majority of individuals are opposed to the community centre, and a percentage are only in favour to protect the first amendment. The U.S. has a chance to extend an olive branch to the Muslim world with this mosque...

Answer 10

OK, so you have lots of answers for the first question.

Now for the second. Why do you need "lightyear" when meter would do just fine to measure distance?