Round disk seen in field across from home in the 70's.

I am reporting a story my mother told me many years ago and recently retold the story so I could report it.  
This happened back in 1974, I was about 3 years old, and my brother was 4 years old and my sister a newborn.  We lived out in the country on a gravel road beside my grandparents. Across the road from us was a field.  My mother could stand in the kitchen and wash dishes and look out at the field.  
She said it was early March and around 6 in the evening before it got dark.  She was at the kitchen sink doing something and glanced out the window to the field.  She said there was a huge round disk hovering above the ground and it was pulsating a pinkish light.  She kept saying it was huge and glowing.  There was no sound coming from it.  It never touched the ground and she said she could see no windows.  
She said it sat there for probably 30 minutes doing nothing but hovering over the ground.  
She said that we, I and brother, went out onto the porch and watched it.  She sent my brother next door to get my grandparents and they came over as well.  She said they just stood there watching it trying to figure out what it was and nobody could explain what it was.  
My grandparents went back home and my sister started crying, my mother went into get her and when she came back out it was gone.  
My mother said it was not anything she had ever seen before or since. She said nothing weird happened and no missing time.  
I found it strange that I have always been interested in them and nobody else in my family is.