Monday, July 14, 2014

Thoughts 19

Thoughts 19

Earlier I have mentioned how because of the human intellect we have to set up standards (reference frames) to try to understand our world, society or anything. This week I want to show some comparisons; reference frames that will borrow from others. I am fat weighing 275 pounds. Comparing my size to a new born of 7 pounds, I am large. Compare my size to the size of the Earth and I am small. I seem to be getting fatter and fatter but I do not believe I will be anything but small if I am compared to the Earth.

I have found illustrations that will show and tell the sizes of the planets and the distances involved in the solar system.

How Distances are Measured in Astronomy

Dealing with the numbers involved with the distances to the stars or even with those found in the solar system can be hard going. Astronomers make their lives easier by using a number of rulers (units of distance) for the distances and although they have some strange names they can be very useful for comparing the distances to stars, other galaxies and even the planets in our solar system.

AU (astronomical units)

One AU is the distance that the average distance that the Earth orbits the Sun at. The AUis most commonly used for the distances of objects with in our solar system. Pluto, the last planet in the solar system is found at an average distance of 39.47 au from the Sun. Sedna the new body nearly as large as a planet found beyond Pluto is never nearer to the Sun than 76AU and then goes to 880AU from the Sun in its giant elliptical orbit.

Light Years

One of the most common rulers is the light year. The light year is is the distance that light travel in one year (365 1/4 days). It is most commonly used for the distances to stars and other galaxies.
The nearest star is 4.2 light years away from our sun. We are 8.3 light minutes away form the Sun. the distance to the outer most planet Pluto is about 13 light hours.
Some other interesting distances in light years:

Distance in light years
Nearest Star (Proxima Centuri)
Sirius the dog star (the brightest star in the sky)
centre of the galaxy
approximately 30 000
Andromeda (one of our nearest neighbouring galaxies)
approximately 2 million
The stars of Orion. (Betelgeuse and Rigel)
1400 light years

Parsec (pc)

Astronomers started measuring distances from the amount that a star moves as the Earth goes from one side of the Sun to the other. Try moving your head and you will see that the postion of everything around you changes. One parsec is derived from the smallest angle measurement of 1/3,600th of a degree or an arc second that is the angle that a star at this distance would appear to move in 6 months as the Earth journeys around the Sun. A parsec is 3.2616 light years or 30,857,000,000,000 km.. Two parsecs is 6.5532 light years or twice the distance, it is not a measure of change in angles of the stars. Due to the massive distance in the universe astronomers often use multiples of parsec commonly found are kiloparsec (kpc) a 1000 parsecs or a megaparsec (Mpc) 1,000,000 parsecs.

Below is a conversion table for some useful astronomical distance units

kilometres (km)
Astronomical units (AU)
Light Years (l.y.)
Parsec (pc)
kilometres (km)
149.6 million
Astronomical units (AU)
Light Years (l.y.)
Parsec (pc)

Planet Radius Radius Object ideal ideal
(Jupiter=1) circumference diameter
Jupiter 68,700 km     1.000    basketball      73.5 cm    23.4 cm
Saturn 57,550 km     0.838    soccer ball     61.5 cm    19.6 cm
Uranus 25,050 km   0.365    softball           26.8 cm    8.52 cm
Neptune 24,700 km  0.360    softball          26.4 cm    8.40 cm
Earth 6,378 km       0.093    large marble  6.81 cm    2.17 cm
Moon 1,738 km      0.025    tiny bead       1.86 cm    5.91 mm
Venus 6,050 km     0.088    large marble  6.47 cm    2.06 cm
Mars 3,394 km      0.049    small marble  3.61 cm   1.15 cm
Mercury 2,440 km 0.036    small bead    2.60 cm    8.30 mm
Pluto 1,700 km     0.025    tiny bead      1.81 cm    5.78 mm
Charon 750 km    0.011    tiny bead      0.80 cm    2.55 mm
The chart is arranged in order of decreasing size, with the only exception being the moon given right after the Earth. **

The reason for all the data is preparing for the next post. I hope you weren't too bored this time.

Pictures are from google and duckduckgo

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