Weight is just a number!

picture from storejpg.com

Weight IS just a number-it’s simply the product of the mass of an object and the force put on that object due to gravity!  Since the number is dependent on gravity, it’s totally logical that, since the force of gravity from the Sun is different in different locations in the Solar system and mass remains the same (close enough, imagining that the object could be at all these places in the universe at the same time), the weight of these objects will also change.  This change is proportional to the gravitational force on the planet, with the proportionality constant being the object’s mass!  This site is a lot of fun for seeing what you, or your favorite object that you know the mass of, would weigh in various other locations in the Solar system.  It’s interesting to see the effects of both distance from the Sun and mass of the solar body on the gravity there, and thus the effect on weight!  For example, a 200 lb person on Earth would weigh only 75.6 lbs on Mercury and 472.8 lbs on Jupiter.  This may be opposite of what one would initially think since Mercury is so close to the Sun and Jupiter is further away, so it seems like you should feel a lot more force due to gravity on Mercury, but you cannot forget to factor in the masses of the two objects! Jupiter is more than 5700 times more massive than Mercury, explaining the huge difference in gravity and the further object actually experiencing more gravitational force from the Sun.  Overall, I had a lot of fun playing around on this site, and it definitely helped me understand a lot more about how the effects of both distance AND mass factor into the force of gravity on each of these solar bodies!

The first navigational tool

Image from kaloujm.com

People have been using the sky as their source of navigation for years, and one of the first tools made for the purpose of aiding in navigation (that wasn’t a body part!) was the kamal.  The exact date is unsure, but it’s estimated that this tool came into use around the fifth or sixth century.  While it looks simple, made of just a piece of wood and some string with strategically tied knots along its length, it was highly effective at measuring relatively small angles, allowing ancient navigators to determine their latitude.  It’s used by placing one end of the string between your teeth and extending out the wooden portion attached to the other end of the string an appropriate distance from your face such that the horizon is along the bottom of the wooden board and the star of interest (usually Polaris) to use for navigation is along the top of the board.  The angle is then measured by counting the number of knots which are tied into the string, and this number corresponds to a certain degree of latitude.  There were clear limitations to this tool, as it had a limit with it’s size and that it could only measure a set (pretty small) amount of angles, so it was only very useful in equatorial regions where Polaris remained very near the horizon.  While we have come a long way in navigational tools over the last several centuries, it’s really awesome to see how something so simple can be such a powerful tool when resources and knowledge are limited.