If a star 100 light years from earth is beginning to expand into a giant star how long will it take for astronomers to observe this development explain

Which is not a source of noise pollution? a)airplanes b)acid rain c)machines d)cars

The place you get your hair cut has two nearly parallel mirrors 6.00 m apart. as you sit in the chair, your head is 2.00 m from the nearer mirror. looking toward this mirror, you first see your face and then, farther away, the back of your head. (the mirrors need to be slightly nonparallel for you to be able to see the back of your head, but you can treat them as parallel in this problem.) how far away does the back of your head appear to be?

Which feature indicates that mars resides in the inner region of the solar system