They have to be - essentially they're the outer envelope.

At the edge of the outer envelope, the aircraft is not yet a threat.

Anyway, I'd be curious to see the numbers for a red giant's outer envelope.

The star would suddenly have nothing to fuse, no means to support its outer envelope against collapse.

But, no- Again he slowly opened the outer envelope.

It is because one or another of the elements doth form their bodies' outer envelope.

Water will often penetrate the outer envelope of a building and appear inside.

Do remember, however, that a post office manages the outer envelope of mail.

Some of the viruses also have an outer envelope.

However, their outer envelope is much lower in temperature, giving them an orange hue.