Central Bureau for Astronomical Telegrams
The Central Bureau for Astronomical Telegrams is an international clearing house that gathers and distributes alerts about transient astronomical events.
Last updated August 31, 2026
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Overview
The Central Bureau for Astronomical Telegrams (CBAT) is an international astronomical information service responsible for collecting, checking, and circulating reports about transient or newly observed events in the sky. Its subject matter includes comets, novae, meteors, natural satellites, and other astronomical phenomena whose discovery, confirmation, designation, or changing brightness may require rapid communication among observatories and researchers. In addition to distributing information, the bureau has historically helped establish discovery priority and circulated initial designations or names for newly reported objects. The organization was established in 1882 by the Astronomische Gesellschaft in Kiel, Germany. During the First World War it moved to Copenhagen, where it was operated through the Copenhagen University Observatory at the Østervold Observatory. The International Astronomical Union subsequently designated the bureau as its official central bureau in 1922, using the French title Bureau Central des Télégrammes Astronomiques. This institutional relationship made CBAT part of the international infrastructure through which astronomers exchanged urgent observations and coordinated information about transient phenomena. The word “telegrams” reflects the bureau’s earlier communications technology rather than its present operating model. From the 1920s through 1992, urgent notices could be sent by telegram, although many circulars were distributed by ordinary mail. As electronic communications became standard, the bureau moved toward electronic distribution. IAU Circulars and related Minor Planet Circulars became available electronically from the mid-1980s, and the Central Bureau Electronic Telegrams, or CBETs, were introduced as a digital expansion of the circular system. CBETs are distributed by email to subscribers and made available through the CBAT website. In 1965, the bureau moved from Copenhagen to the Harvard College Observatory in Cambridge, Massachusetts, where it was operated by the Smithsonian Astrophysical Observatory. Harvard had already maintained a western-hemisphere central bureau from 1883, allowing its staff and facilities to assume responsibility for the international bureau. In 2010, operational responsibility moved from the Smithsonian Astrophysical Observatory to Harvard University’s Department of Earth and Planetary Sciences. The bureau has remained in Cambridge since its relocation to the Harvard environment. CBAT is a nonprofit service rather than a conventional commercial brand. It charges for access to IAU Circulars and electronic telegrams, with those fees supporting the service’s continuing operation. Its role is specialized: it functions as a trusted distribution and coordination point for professional astronomers, observatories, and other qualified users who need timely information about transient celestial events. The organization’s historical identity is tied to telegrams, but its contemporary communications depend on email, web publication, and electronic circulars. Its institutional importance lies in preserving an organized international record of observations and in helping the astronomical community coordinate recognition, naming, and follow-up of rapidly changing phenomena.
History
The Central Bureau for Astronomical Telegrams originated in 1882, when the Astronomische Gesellschaft established it in Kiel, Germany, to coordinate the exchange of urgent astronomical information. Its early purpose was closely connected with the practical difficulty of communicating discoveries and unusual observations across national borders. Reports concerning comets, novae, meteors, and other transient events could affect observing priorities, discovery credit, and the work of astronomers who needed to verify or follow up an event quickly. During the First World War, the bureau was moved to Copenhagen and operated through the Copenhagen University Observatory at the Østervold Observatory. In 1922, the International Astronomical Union formally made the Central Bureau its official bureau for astronomical telegrams. The organization was then also known by the French designation Bureau Central des Télégrammes Astronomiques, reflecting the multilingual and international character of astronomical institutions of the period. For much of the twentieth century, the bureau distributed information through a mixture of telegrams, printed circulars, and ordinary mail. Urgent telegram transmission continued from the 1920s until 1992, although telegrams were not the only communication channel. The term “telegram” survived after the technology ceased to be central because it had become part of the institution’s established name and identity. The service’s information role included not only reporting observations but also helping establish discovery priority and communicating provisional designations or names for newly recognized objects. The bureau moved to the Harvard College Observatory in Cambridge, Massachusetts, in 1965. The Harvard institution had maintained a western-hemisphere central bureau since 1883, and its staff therefore had relevant experience in receiving and circulating astronomical reports. After the relocation, the bureau was operated by the Smithsonian Astrophysical Observatory on the Harvard University campus. This arrangement connected CBAT with a major research environment while preserving its international function under the International Astronomical Union. Electronic communications gradually transformed the service. From the mid-1980s, IAU Circulars and related Minor Planet Circulars became available electronically. Later, the Central Bureau Electronic Telegrams were established as a digital-only extension of the circular system. CBETs could be distributed to subscribers by email and posted on the bureau’s website, allowing information to travel more rapidly than printed circulars or postal notices. The change modernized delivery without eliminating the bureau’s traditional role as an authoritative clearing house. In 2010, responsibility for operating CBAT moved from the Smithsonian Astrophysical Observatory to Harvard University’s Department of Earth and Planetary Sciences. The bureau continued to operate from Cambridge. It remains a nonprofit service and charges for its IAU Circulars and electronic telegrams in order to finance ongoing operations. Today, CBAT’s institutional value comes from its specialized position within international astronomy: it provides a recognized channel for transient-event information, supports coordinated observation, and maintains continuity between historical astronomical communication practices and modern digital alert distribution.
- 2010
Operational transfer within Harvard
[1]Operation of CBAT moved from the Smithsonian Astrophysical Observatory to Harvard University’s Department of Earth and Planetary Sciences.
- 1992
Traditional telegram transmission ends
[1]The bureau’s historical use of urgent telegram transmission ended, although the word remained in its name.
- 1985
Electronic access to circulars begins
[1]IAU Circulars and related Minor Planet Circulars became available electronically during the mid-1980s.
- 1965
Relocation to Harvard College Observatory
[1]CBAT moved from Copenhagen to Cambridge, Massachusetts, where it was operated by the Smithsonian Astrophysical Observatory.
- 1922
IAU designates CBAT as its official central bureau
[1]The International Astronomical Union made the organization its official central bureau for astronomical telegrams.
- 1883
Harvard western-hemisphere bureau begins operating
[1]Harvard College Observatory maintained a separate western-hemisphere central bureau, an institutional predecessor relevant to its later operation of the international bureau.
- 1882
Central Bureau established in Kiel
[1]Astronomische Gesellschaft founded the Central Bureau in Kiel, Germany, to coordinate information about transient astronomical observations.
Products and positioning
A specialized, internationally coordinated information clearing house for professional astronomical alerts and transient-event reporting.
Astronomical circulars
IAU Circulars
IAU Circulars are notices used to communicate significant information about transient astronomical events, including observations and reports concerning comets, novae, meteors, natural satellites, and other newly observed phenomena. Historically distributed by mail and, in urgent cases, telegram, they later became available electronically. Access fees help support CBAT’s nonprofit operations.
Digital astronomical alerts
Central Bureau Electronic Telegrams
Central Bureau Electronic Telegrams, commonly called CBETs, are the bureau’s digital-only extension of its traditional astronomical circulars. They provide timely notices about transient events and are distributed by email to subscribers as well as made available through the CBAT website. The service preserves the historical telegram designation while using modern electronic delivery.
Brand decisions
2010
Transfer operation to Harvard’s Earth and Planetary Sciences departmentStrategyBackground
CBAT had been operated by the Smithsonian Astrophysical Observatory since its relocation to Harvard in 1965.
Action taken
Operational responsibility moved to Harvard University’s Department of Earth and Planetary Sciences.
Aftermath
The bureau remained in Cambridge while its operating institutional home changed within Harvard’s scientific structure.
1985
Adopt electronic distributionStrategyBackground
Electronic communications began replacing printed and mailed notices as the faster method for distributing astronomical information.
Action taken
IAU Circulars and related Minor Planet Circulars were made available electronically during the mid-1980s.
Aftermath
CBAT’s information reached subscribers more quickly and the organization began its transition from traditional correspondence toward digital delivery.
1965
Move the international bureau to HarvardStrategyBackground
The International Astronomical Union’s central bureau had operated in Copenhagen since its wartime relocation. Harvard already maintained a western-hemisphere bureau and had institutional experience with astronomical information exchange.
Action taken
CBAT was transferred to the Harvard College Observatory in Cambridge, Massachusetts, where the Smithsonian Astrophysical Observatory assumed operational responsibility.
Aftermath
The bureau established a long-term base in Cambridge and continued its international clearing-house role from the Harvard environment.
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