Arecibo Observatory is presented as the point of origin for humanity’s 1974 SETI message to a distant globular cluster. In Samantha Crowe’s account of how communication with the Yrr might work, the observatory becomes more than a transmitter: the message describes the human world through mathematics and includes an image of the device that sent it. Its role links a specific terrestrial instrument to the much larger question of how one intelligence might make itself intelligible to another.

The 1974 transmission

Crowe explains that the 1974 message was sent from the Arecibo radio telescope toward a globular cluster in the constellation of Hercules. It comprised 1,679 characters encoded as binary pulses. The number was chosen for its mathematical structure: it is the product of the prime numbers 23 and 73, allowing a recipient to arrange the pulses as 73 columns of 23 characters and reveal a pattern.

The transmission’s journey underscores the distance between sending a signal and establishing contact. Crowe estimates that the message would take 26,000 years to reach its destination and that a reply would take another 26,000 years to return. Against this timescale, the novel’s proposed underwater exchange with the Yrr is presented as a much faster alternative.

What the message depicts

The message’s visual structure is designed to carry information across differences in language and measurement. Its upper lines show the numbers one through ten and indicate the decimal system. Further sections give the atomic numbers of water, carbon, oxygen, nitrogen, and phosphorus, followed by information about Earth’s biochemistry, including DNA bases, sugars, and the double helix.

The final third depicts the human form and links it to DNA, inviting the recipient to infer something about evolution on Earth. Because human units of length would mean nothing to an alien intelligence, the signal’s wavelength supplies a reference for average human height. The message then diagrams the solar system and concludes with the appearance, dimensions, and design of the Arecibo radio telescope itself. The instrument is thus made part of the introduction: the sender attempts to show not only what humanity is, but how it communicated.

Role in the first-contact discussion

Crowe presents the Arecibo transmission while explaining why mathematics might serve as a common language for beings subject to the same physical laws. She distinguishes the distant, one-way message from the planned underwater contact, which is to proceed in stages and begin with two sums intended to establish the Yrr’s existence and test whether dialogue is possible.

The discussion also turns the message’s invitation into a question of risk. Vanderbilt characterizes it as an invitation to visit Earth and consume humanity; Crowe acknowledges that this danger concerned the authorities, but argues that an invitation was unnecessary because Earth had already been broadcasting radio waves for decades. Ordinary radio traffic, including intelligence-agency communications, could itself disclose the existence of a technologically capable civilization. Arecibo therefore embodies both the ambition and the vulnerability of deliberate contact: a carefully structured message may make its sender legible, but it cannot control what the recipient learns or chooses to do.