To send content items to your account,
please confirm that you agree to abide by our usage policies.
If this is the first time you use this feature, you will be asked to authorise Cambridge Core to connect with your account.
Find out more about sending content to .
To send content items to your Kindle, first ensure firstname.lastname@example.org
is added to your Approved Personal Document E-mail List under your Personal Document Settings
on the Manage Your Content and Devices page of your Amazon account. Then enter the ‘name’ part
of your Kindle email address below.
Find out more about sending to your Kindle.
Note you can select to send to either the @free.kindle.com or @kindle.com variations.
‘@free.kindle.com’ emails are free but can only be sent to your device when it is connected to wi-fi.
‘@kindle.com’ emails can be delivered even when you are not connected to wi-fi, but note that service fees apply.
The study of the nongravitational effects on comets began slightly more than a century and a half ago. As is well known, Encke (1819) demonstrated that comet 1819 I had a revolution period of not more than a few years and that the same comet had also been observed in 1786, 1795 and 1805. The observations clearly required that the revolution period be about 3.3 years, and Encke went on to remark that, after approximate allowance had been made for the perturbations by the planets, the average revolution period seemed to be 1207.9 days between 1795 and 1805, but only 1207.3 days between 1805 and 1819. As a result of a more refined computation of the planetary perturbations, the following year he (Encke 1820) was able to confirm these figures and find in addition that the average period between 1786 and 1795 was as much as 1208.1 days.
Among the solar proxies, κ1 Cet, stands out as potentially having a mass very close to solar and a young age. We report magnetic field measurements and planetary habitability consequences around this star, a proxy of the young Sun when life arose on Earth. Magnetic strength was determined from spectropolarimetric observations and we reconstruct the large-scale surface magnetic field to derive the magnetic environment, stellar winds, and particle flux permeating the interplanetary medium around κ1 Cet. Our results show a closer magnetosphere and mass-loss rate 50 times larger than the current solar wind mass-loss rate when Life arose on Earth, resulting in a larger interaction via space weather disturbances between the stellar wind and a hypothetical young-Earth analogue, potentially affecting the habitability. Interaction of the wind from the young Sun with the planetary ancient magnetic field may have affected the young Earth and its life conditions.
Databases of astrometric and orbital data for minor planets and comets and of photometric data for comets are maintained in connection with the publication of the Minor Planet Circulars and the International Comet Quarterly. Aspects of these publications and the content and availability of these databases are discussed.
Although there are currently no professional search programs specifically designed for comets, comet discoveries are a significant by-product of the current search programs for near-earth asteroids. With their emphasis on the opposition point and the ecliptic, asteroid patrols are clearly biased toward discovering short-period comets. A. comparison of the comet discoveries made at elongations of less than 120° from the sun during the ten-year intervals ending in 1892 and 1992 indicates that the current opposition searches are not able to displace visual searches in the vicinity of the sun. Modification of the near-opposition search region to that proposed for the Spaceguard Project would be helpful, but—as also proposed for Spaceguard—supplementation is still necessary for high-inclination objects. CCD experimentation in the regions traditionally searched visually by amateurs would be useful. Searches for particular types of object like Kreutz sungrazers and comets near Jupiter in space are briefly discussed.
Launched in October 1990, the ESA-NASA Ulysses mission has conducted the very first survey of the heliosphere within 5 AU of the Sun over the full range of heliolatitudes. The first polar passes took place in 1994 and 1995, enabling Ulysses to characterise the global structure of the heliosphere at solar minimum, when the corona adopts its simplest configuration. The most important findings to date include a confirmation of the uniform nature of the high-speed (~ 750 km s−1) solar wind flow from the polar coronal holes, filling two-thirds of the volume of the inner heliosphere; the sharp boundary, existing from the chromosphere through the corona, between fast and slow solar wind streams; the latitude independence of the radial component of the heliospheric magnetic field; the lower-than-expected latitude gradient of galactic and anomalous cosmic rays; the continued existence of recurrent increases in the flux of low-energy ions and electrons up to the highest latitudes.
Introduction: Vancouver Coastal Health (VCH) emergency physicians have been on contract based funding models for two decades. On October 1, 2015, physicians at one hospital (SPH) switched to fee-for-service (FFS) payments. Conventional wisdom is that FFS physicians are motivated to see more patients quickly and achieve higher throughput. Our hypothesis was that FFS payment would reduce patient wait times. Methods: This interrupted time series analysis with concurrent control was performed in VCH Region, where there are two tertiary EDs. During the 20-week study period (July 15-Nov 30), VGH remained on contract, while SPH converted to FFS (the intervention). VCH administrative data was aggregated by week. Our primary outcome was median wait time to MD. Secondary outcomes were ED LOS and left-without-being-seen (LWBS) rates. Results: Interrupted time series plots will be presented for the data. Data from 67,214 ED visits were analyzed (31,733 SPH, 35,481 VGH). Figure 1 shows that baseline wait time was 74 minutes at the control and 53 minutes at the intervention site. During the pre-intervention period, there was a non-significant downward trend of 0.4 minutes per week at the intervention hospital relative to control (p=0.26). After FFS conversion, there was a 4.1 minute increase in wait time at the control site (p=0.18), and a significant downward trend of 1.4 minutes per week (p=0.001). After FFS conversion, wait times at the intervention site increased by 4.8 minutes more than control (p-value for the difference=0.27), and the wait time trend increased significantly by 1.3 minutes per week relative to the expected counterfactual trend (p=0.02). Baseline EDLOS for discharged patients was 227 minutes at the control hospital and 193 minutes at the intervention site. There were similar pre-intervention LOS increases at both hospitals. Post-intervention, both sites saw significant increases in EDLOS, followed by a similar downward trends of -2.68 minutes per week (p=0.001). Baseline LWBS rate was 3.86% at the control hospital and 3.56% at the intervention site. Pre-intervention trends, and post-intervention level/trend changes did not differ by site. Conclusion: Conversion to FFS payment was associated with an increase in wait time trend of 1.3 minutes per week relative to control. There were no significant changes in EDLOS or LWBS rates. In this preliminary analysis, FFS payment had little effect on wait times or patient throughput.
In the past triennium members of the Commission 20 have been very active in studying positions and motions of minor planets, comets and satellites including rings by observational and theoretical investigations, as it is described in this report In fact observers have been producing tremendous amount of astrometric data, much more than we could imagine twenty years ago, when we heard many complains and appeals to observers for needs of more observations, particularly, for minor planets and satellites. Technically, several new devices to detect faint objects and to measure their positions more effectively, have been developed. Theoreticians have faced many interesting and important problems to explain observational facts with several powerful methods developed recently.
As noted below in the report of the Central Bureau, a number of changes have been introduced in the technical and business operations of the Bureau during the triennium. Some of the changes follow from the transfer of the IAU Minor Planet Center to the Smithsonian Astrophysical Observatory. For example the Minor Planet Circulars now offer an alternate avenue of publication for less time-urgent data concerning comets as well as minor planets. Changes at the communications center of the Smithsonian Astrophysical Observatory have made it less costly, as well as more efficient, for the Central Bureau to maintain its own communications equipment. At the same time, in the face of generally rising costs, and after careful investigation of alternatives, it has become necessary for users to assume an increased share in underwriting the operating expenses of the Bureau.
Since July 1996, 815 new names on features on bodies in the Solar System have been assigned by the WGPSN and approved at the IAU General Assembly in Kyoto in 1997. Of these names, 666 were for Venus, 17 for Mars, 3 for the Moon, 125 for the Galilean satellites, 3 for the Uranian satellite Miranda, and 1 for the minor planet Ida. 71 additional names mostly on Venus have been selected and have been given or are awaiting provisional approval by the IAU Executive Committee (EC). These names are up for final approval at the next IAU General Assembly.
The year 1990, within the triennium covered by the present report, marked a number of significant anniversaries for the Central Bureau, including 70 years since its foundation at the Brussels Observatory, 25 years since the transfer of the Bureau’s operations to the Smithsonian Astrophysical Observatory (and 22 years of Dr. Marsden’s service as Director), and the issuance of the 5000th Circular. The amount of work done at the Bureau has increased enormously in this time, but especially within the past decade, as a result of the demands of modern astronomers and astrophysicists who are responding to the technological advances that have revolutionized observing and computing methods. At the same time methods of rapid communication have undergone a transformation that still continues. Appreciation is due for the support provided to the Bureau by the Smithsonian Astrophysical Observatory, but special gratitude must be expressed to Dr. Marsden and members of the staff and volunteers for their long hours of work and dedication to the needs of astronomers around the world for rapid access to information.
Throughout the triennium, Commission 6 has interacted with the Central Bureau for Astronomical Telegrams (CBAT), most ably headed by Brian Marsden. As will be seen from his report below, the use by scientists of the Circulars for rapid dissemination of astronomical and related news continues unabated.
The commission has been able to continue its work during the last triennium with a minimum of effort. Thanks for this and for the untiring dedication are due to the Director of the Bureau, B. G. Marsden. We are also grateful to the Smithsonian Astrophysical Observatory for its general support.
According to the annoucement published in the IAU Information Bulletin no 58, K. A. Thernöe died on 1987 March 7. He was the director of the Central Telegram Bureau during the years 1960 - 1964 in Copenhagen and for many years he served as principal substitute for Julie Vinter Hansen when she ran the Bureau.
During the triennium, Commission 6 continued to interact with the Central Bureau for Astronomical Telegrams (CBAT) under the very effective directorship of Brian Marsden. A widening of the associated astronomical subjects recorded in the IAU Circulars was noted. There is no doubt that these Circulars continue to play an important role for the fast dissemination of astronomical information. The trend towards a preference for electronic distribution by the recipients cannot be overlooked.