"Planetarium" is a 45-line free verse feminist poem that starts with a dedication to the eighteenth-century female astrologer Caroline Herschel, explaining that the poem was written while:

Thinking of Caroline Herschel (1750—1848)
astronomer, sister of William; and others.

As the poem continues to talk about the struggles of women, and particularly how women struggle to express themselves in a patriarchal society, the reader realizes the heartfelt anger the quiet, unobtrusive dedication disguises. The line "sister of William," for example, sounds like Rich is saying that despite all she did, Herschel's achievements have always been linked to a man. In this respect, she is dedicating this poem to Herschel and any other women whose brilliance the world has forgotten or revised to better suit male narratives.

The first verse of the poem starts with the lines,

A woman in the shape of a monster
a monster in the shape of a woman
the skies are full of them

From the beginning, she states exactly what women are up against. If they step out of conventional society and its gendered expectations, society will see them as "monsters"—women who are not palatable or desirable and present a threat to everyday living. The skies are a great example because many of the constellations are named after women who have suffered violence and humiliation because of their gender. The poet continues to talk about the achievements of Caroline Herschel:

in her 98 years to discover
8 comets

She describes Herschel at work in very romanticized terms. It is as if the poet is saying that Herschel should be one of the deities in the skies alongside the male ones:

she whom the moon ruled
like us
levitating into the night sky
riding the polished lenses

As Rich states, however, Herschel was "like us." Like all successful women, she suffered for her "impetuousness."

Galaxies of women, there
doing penance for impetuousness
ribs chilled
in those spaces of the mind

Rich continues on to say that at some point this "galaxy of women" will appear like a nova in the sky.

every impulse of light exploding
from the core
as life flies out of us
If they work together, they can gather strength and change the world.
I am an instrument in the shape
of a woman trying to translate pulsations
into images for the relief of the body
and the reconstruction of the mind.