Timetables are everywhere. In our day-to-day lives, we use basic calendars, diaries and schedules to stay organised and manage our time. They could be to keep track of our own daily tasks and events, or they could be for the public to know about important times such as when trains arrive or when sporting matches will be on. Businesses and hospitals also need timetables to keep track of the many tasks and people that make them run.
Most timetables are structured in a similar way, as a consecutive list of days and/or times. The following schedules from timeanddate.com are the most common types you will encounter.
There are particular patterns in nature that scientists can predict with a high level of accuracy, often years in advance. This is nature's timetable. It includes the motion of the stars and the planets, the variations of the tides, the phases of the moon, and the rising and setting of the sun.
What do all of these have in common? They are all to do with the movement of celestial bodies (things in space). Even the tides depend on where the sun, the moon and the earth are positioned.
Humans have been observing and tracking the motion of stars, planets and the moon since before Ancient times. The Egyptians, the Babylonians and Australian Aboriginals all wrote down early versions of star charts. Stars have determined spiritual practices and beliefs, and helped ships to navigate the ocean.
So how is the movement of celestial bodies different from, say, the changing of the seasons?
Well, even though we can predict when the seasons will occur, things like the weather are too complicated to predict well in advance with accuracy. The movement of celestial bodies, on the other hand, is one of the most predictable things in all of science.
For this reason, we have timetables for the tides, the phases of the moon, and sunrise/sunset.
However, these timetables often aren't formatted like the basic timetables above. Why might this be? What would it look like if we tried to use one of the above styles?
Well, one reason for using a different format is that these natural events are only occurring two or four times a day at most. Secondly, there is a lot of information associated with these events that we want to know, such as heights of the tides or time differences between sunrise and sunset. Thirdly, they are not occurring at nice half-hourly intervals. Sometimes, they aren't even occurring the same amount of times each day! For instance, most of the time, there are two high tides and two low tides each day. However, sometimes only three tide extremes can fit in a day, and not all days begin with a low tide.
We will now try to interpret some complex timetables such as these.
Consider the following timetable.
A good way to understand the phases of the moon is to view an animation. Further details, diagrams and selected animations can be found here.
One full revolution of the Earth is a day. One full revolution of the Earth around the Sun is a year.
Firstly, notice just how slowly the Moon moves around us. Even though we talk of sunrises, sunsets, moonrises and moonsets, in reality, it is the earth that is doing the moving.
Secondly, notice that the Moon is almost always lit. It does not matter what phase the Moon is in, half of the moon is always lit by the Sun. The Earth's position relative to the Moon and Sun is the reason why we don't always see a Moon which is half lit and the phases of the Moon which we see is the determined by the potion of the lit Moon we can see from the Earth's position relative to the position of the Sun and the Moon.
The Moon does not appear lit during a lunar eclipse, which only happens a small number of times a year at most. This is when the Moon passes directly behind the Earth and into its shadow, with the Sun, Earth and Moon closely aligned,
Thirdly, notice also that on any particular night, the moon is in a different position in relation to the Earth and the Sun. Sometimes it is between the two, sometimes it is to the side of the Earth, and sometimes it is behind the Earth. This determines what part of the lit moon we can see at night, called the moon phase.
(a) When is the next Full Moon? Where will the Moon be in relation to the Earth and the Sun on that night?
(b) When is the next New Moon? Where will the Moon be in relation to the Earth and the Sun on that night?
(c) When is the next Crescent Moon? Where will the Moon be in relation to the Earth and the Sun on that night?
(d) Approximately how many days are there between Full Moons? This is called a Lunar Month.
(e) Approximately how many Lunar Months are there in a year?
2. Another name for a Lunar Month is a Synodic Month, the amount of time between Full Moons. On the other hand, a Sidereal Month is the amount of time it takes the Moon to orbit 360 \deg around the Earth. These are not the same. A Sidereal Month is about two days shorter than a Synodic Month. Why do you think this is? Discuss with your classmates and your teacher.
The words Moon and Month come from the same Latin word.
Moon phases, the changing of the seasons, and later the calculation of the Earth's orbit around the Sun, are the ways humans have historically used to define the calendar year.
Most people are used to having four seasons- Summer, Autumn, Winter and Spring. However, some indigenous calendars divide the year up differently based on subtle changes in the natural environment. For example, the Yarwuru tribe has seven seasons, while the Miriwoong tribe only has three.
Indigenous Australians observed the relationship between changes in the astronomy and corresponding changes in flora and fauna. Stories about the rising and setting stars and constellations, as well as movements of the sun, moon and planets were passed on to teach people when it was time to move on and find a new source of food.
There is evidence Aboriginal Australians may actually have been some of the first astronomers. For example, according to oral tradition, the rock engravings by the Nganguraku people at Ngaut Ngaut (shown at the top of the page) represent lunar cycles. Lunar cycles influences the tides. Tides are caused by the gravitational pull of the sun and moon, which can be used to tell the time.
Ben and his friends are planning a surfing and fishing holiday for the coming week near Triggs Beach in Western Australia. Ben checks the surf forecast for a beach where they are staying to help plan for the week ahead.
Ben knows that a falling tide, which is about two hours before a low tide, are the best conditions for fishing. Ben and his friends don’t mind fishing in the rain. For surfing at this spot, high tide, above about 0.5 m, tends to be the best and surfers usually prefer to surf when the weather is clear and at dawn and dusk.
interpret complex timetables, such as tide charts, sunrise charts and moon phases