Track quiz
Show on a big screenHere are the nine rules, in the exact words each lab uses.
| Idea | The rule, as the lab applies it |
|---|---|
| A day | The Earth spins on its axis. So the Sun seems to rise and set. The time from one highest Sun to the next is a day. It is about 24 hours. |
| A shadow that tells the time | A stick's shadow is shortest when the Sun is highest. The time from one shortest shadow to the next is one day. |
| A month | The Moon shines by reflecting sunlight. Half of the Moon is always lit. We see only the part of the lit half that faces us. So the Moon seems to change shape. The cycle takes about 29.5 days. |
| A year | The Earth goes once round the Sun in about 365¼ days. During this time the seasons go through one cycle. That cycle is a year. |
| They do not divide | Twelve Moon months make 354 days. A solar year is about 365 days. So twelve Moon months fall short by nearly 11 days. |
| A spare day every few years | Earth's trip round the Sun takes a bit less than 365¼ days. Four quarter days make about one extra day. So a year divisible by 4 is usually a leap year. A century year must divide by 400. |
| Calendars people use | A lunar calendar follows the Moon. A solar calendar follows the seasons. A luni-solar calendar follows the Moon. It adds an extra month every few years. That keeps it in step with the seasons. |
| Where to look for the Moon | At sunset, look for a waxing Moon. At sunrise, look for a waning Moon. |
| Satellites above us | Artificial satellites are human-made and orbit the Earth. They help with research, weather, communication, disasters and navigation. |
What makes the Sun seem to rise and set?
About how long is a day?
The shortest shadow comes at 12:40 on two days in a row. How long is the day?
When is a stick's shadow shortest?
You see no lit part of the Moon at all. What phase is it?
Why does the Moon seem to change shape?
About how long does one cycle of Moon phases take?
What repeats once in a year?
How many days do twelve Moon months make?
A solar year is about 365 days. Twelve Moon months make 354. What is the gap?
Why is there a leap year?
Which of these is a leap year?
A calendar follows the Moon. It adds a month every few years. What kind is it?
Why do festivals on the Moon's dates move on the Gregorian calendar?
A thin Moon is low in the west just after sunset. What is it?
An object orbits the Earth and carries TV between far places. What is it?
Chapter 11 of your NCERT book is Keeping Time with the Skies. Read it now. Ask of each cycle: what spins or goes round?
Next: How Nature Works in Harmony.
Reveal every answer to finish this lesson.