Please read the following table in Markdown format and then answer the question according to the table. Table cells in one row are seperated by '|', and different rows are seperated by '
'.

Table:
| Episode title | Subject | Music by | Performed by | First aired |
| --- | --- | --- | --- | --- |
| The Body Machine | Nutrition and digestive system | Lynn Ahrens | Bob Dorough and Jack Sheldon | 1979.0 |
| Electricity, Electricity | Electricity | Bob Dorough | Zachary Sanders | 1979.0 |
| The Energy Blues | Energy conservation | George Newall | Jack Sheldon | 1978.0 |
| Interplanet Janet | The solar system | Lynn Ahrens | Lynn Ahrens | 1978.0 |
| Telegraph Line | Nervous system | Lynn Ahrens | Jaime Aff and Christine Langner | 1979.0 |
| Them Not-So-Dry Bones | Skeletal system | George Newall | Jack Sheldon | 1979.0 |
| A Victim of Gravity | Gravity | Lynn Ahrens | The Tokens | 1978.0 |
Question:
If skeletal system is the subject when was it first aired?
Answer:
1979.0