Commission 31 activities

Consistent with its Terms of Reference, Commission 31 acts as a coordinating body for discussions and meetings related to time. A major focus of these activities occurs at each IAU General Assembly when Commission Business Meetings and associated Joint Discussions are held. Links to Commission 31 Triennial Reports and Business Session Reports are given below.

Joint Discussions
C31 Triennial Reports
Business Session Reports
Circular Letters (2001 - 2003)

Working groups

Commission 31 members participate in IAU Working Groups, mostly under Division I. Current activities include:

Leap Seconds

For the past several years, a proposal to eliminate the "leap seconds" from UTC has been under discussion and Commission 31 members have contributed to this process. Leap seconds are inserted in UTC as necessary to maintain synchronicity with the rotation of the Earth (see the BIPM webpage for definitions of the various international timescales). A detailed discussion of the history of the leap second and possible future developments is given in the Metrologia (2001) article by R. A. Nelson et al.. Please note, an extensive series of articles on timescales and time standards has been published in Volume 48 of Metrologia.

An IAU Working group on the topic was set up in 2000 and produced a final report in July 2006 after extensive consultation. At that time, there was no consensus on whether or not to eliminate leap seconds from UTC. Since then, opinion has shifted toward eliminating leap seconds from UTC. This discussion and the processes involved were discussed by D. McCarthy at Joint Discussion 6, 27th IAU General Assembly, August 2009.

A useful web page describing developments in this process and giving many associated links is maintained by Steve Allen.

Recent Developments

Working Party 7A (Time Signals and Frequency Standard Emissions) of the International Telecommunications Union (ITU) met in Geneva on 5-11 October, 2010. During this meeting the possible revision of ITU-R TF 460-6 to abolish leap seconds from UTC was discussed. Prior to this meeting, the IAU was requested to report on whether or not it supported this proposal. A poll of Commission 31 members especially requesting input from those opposed to the recommendation resulted in three opposing responses. Several responses supporting the recommendation were also received. Based on this and other input from IAU members, the IAU submitted a document to the ITU supporting the proposed change.

The following report on the outcome of the ITU WP 7A meeting was received from Dr Felicitas Arias, Director, Time, Frequency and Gravimetry Department, BIPM, on 28 October, 2010.

"The Study Group 7 (SG7) of the ITU-R met in Geneva in October 2010. Prior to this meeting, eleven ITU Member States responded to a questionnaire circulated by the SG7 on the modification of the recommendation ITU-R TF.460-6 which proposes a redefinition of UTC without leap seconds. Two international organizations, the IAU and the BIPM also sent answers, and they were considered as qualified opinions. The three administrations opposing the recommendation did not add any technical information to the discussion. Therefore, the President of the SG7 decided on the meeting of 12 October to send the proposed revision of Recommendation ITU-R.460-6 to the Radio Assembly which will meet in Geneva between the 16 and the 20 January 2012. A consultation to the Member States will be put in place, informing that the recommendation will be submitted to the Radio Assembly, and requesting responses to the questionnaire. A vote on the recommendation will take place during the Radio Assembly, and at least 70% of favourable votes will be necessary for the approval of the proposal."

Dr Masatoshi Ohishi, the IAU's representative on the ITU, has forwarded the section of the SG7 Chairman's report that relates to Recommendation ITU-R TF.460-6 on leap seconds:

"Results of discussions on the revision of Recommendation ITU-R TF.460-6.
Following further responses to the questionnaire sent by the Director of the Bureau it appeared that 8 Administrations were in favour of the revision of Recommendation ITU-R TF.460-6 while 3 were against it. Since no consensus could be reached the Chairman proposed to send the revision of Recommendation ITU-R TF. 460-6 to the Radiocommunications Assembly together with a report describing the difficulties encountered by Study Group 7 in the revision of the Recommendation. Canada, on behalf of several Administrations, proposed to wait for further responses to the questionnaire prior to next meeting of WP 7A before sending the document to the Radiocommunications Assembly. The USA opposed this proposal. ESA requested a quick decision on this Recommendation in view of the design of GALILEO. UK proposed to wait for the next SG 7 meeting before taking any action on this Recommendation. China proposed to send back the Recommendation to WP 7A. After further debate it was decided to send the Recommendation to the Radiocommunications Assembly, and then to send a new circular letter reminding Administrations to answer to the questionnaire on this issue."

Dr Ohishi also notes that: "The chairman of SG7 was not able to get a consensus regarding the proposed revision of Recommendation ITU-R TF.460-6, and he followed the rule of the ITU when a Study Group can not find a consensus among participants.
The IAU is a recognized international organization in the ITU and is not a Member State. It is the rule of the ITU that only Member States have the right to vote toward making final decisions of the ITU."

Technical Committee 37 of the International Organisation for Standardization (ISO) has issued a statement concerning the naming of a new continuous timescale which has been forwarded to the ITU Radio Assembly for consideration.

Recent meetings about leap seconds:

  • A meeting, Decoupling Civil Timekeeping from Earth Rotation, to discuss potential impacts of the abolition of leap seconds was held in Exton PA, near Philadelphia, USA on 5-6 October 2011. The proceedings of the meeting are available from the publisher. Preprints, presentations and transcripts of the roundtable discussions are also available from a link on the meeting web page.
  • A meeting, Royal Society Meeting: UTC for the 21st century, to discuss the future of the role of UTC was held in Newport Pagnell (near London), UK on 3-4 November, 2011. A short summary of the meeting outcomes was prepared by Dr Terry Quinn and Dr Felicitas Arias, the meeting Chairs.

At its January 2012 meeting in Geneva, the International Telecommunications Union has decided to postpone a decision on the future of leap seconds until 2015 because of differing views of member countries. See the ITU press release for further details.

The IERS announced through Bulletin A (12 January 2012) and subsequently inserted a positive leap second into UTC on 30 June 2012.