space
For every 15° that one travels eastward, the local time moves one hour ahead. Similarly, travelling West, the local time moves back one hour for every 15° of longitude.
Therefore, if we know the local times at two points on Earth, we can use the difference between them to calculate how far apart those places are in longitude, east or west.
This idea was very important to sailors and navigators in the 17th century. They could measure the local time, wherever they were by observing the Sun, but navigation required that they also know the time at some reference point, e.g. Greenwich, in order to calculate their longitude. Although accurate pendulum clocks existed in the 17th century, the motions of a ship and changes in humidity and temperature would prevent such a clock from keeping accurate time at sea.King Charles II founded the Royal Observatory in 1675 to solve the problem of finding longitude at sea. If an accurate catalogue of the positions of the stars could be made, and the position of the Moon then measured accurately relative to the stars, the Moon's motion could be used as a natural clock to calculate Greenwich Time. Sailors at sea could measure the Moon's position relative to bright stars and use tables of the Moon's position, compiled at the Royal Observatory, to calculate the time at Greenwich. This means of finding Longitude was known as the 'Lunar Distance Method'.
Therefore, if we know the local times at two points on Earth, we can use the difference between them to calculate how far apart those places are in longitude, east or west.
This idea was very important to sailors and navigators in the 17th century. They could measure the local time, wherever they were by observing the Sun, but navigation required that they also know the time at some reference point, e.g. Greenwich, in order to calculate their longitude. Although accurate pendulum clocks existed in the 17th century, the motions of a ship and changes in humidity and temperature would prevent such a clock from keeping accurate time at sea.King Charles II founded the Royal Observatory in 1675 to solve the problem of finding longitude at sea. If an accurate catalogue of the positions of the stars could be made, and the position of the Moon then measured accurately relative to the stars, the Moon's motion could be used as a natural clock to calculate Greenwich Time. Sailors at sea could measure the Moon's position relative to bright stars and use tables of the Moon's position, compiled at the Royal Observatory, to calculate the time at Greenwich. This means of finding Longitude was known as the 'Lunar Distance Method'.
parallax
Parallax is where things closer to you seem to move fast while distant trees seem to move slower and mountains in the far distance slower still. We can use parallax to measure distances. For example if you wanted to measure how far away a tree was you could take a picture of the tree with a mountain in the background and drive along the road a little while then take another picture and you would see that the tree had moved in relation to the mountain. If you knew how far you had driven along the road you could use simple maths to work out how far the tree was from you.
This is how we calculate the distance to distant stars but instead of travelling down the road we use the earth's orbit of the sun.
This is how we calculate the distance to distant stars but instead of travelling down the road we use the earth's orbit of the sun.
Immanuel Kant and john flamsteed
Among other things, Kant believed that the concepts of space and time are integral to all human experience, as are our concepts of cause and effect. John Flamsteed was the first astronomer royal in 1675.