MS-072: Adin B. Thayer, Co. B, 16th Maine Volunteer Infantry

This collection contains twenty-one Civil War era letters, ranging from 1862-1865, written by Adin Thayer of the 16th Maine. Most of his letters are written to family members prior to his capture and imprisonment in the Confederate prison camp in Salisbury, North Carolina. The final letter in the collection is dated April 26th, 1865 and is addressed to Thayer’s father from Sgt. William Fennelly, of the 16th Maine informing him of his son’s death. Special Collections and College Archives Finding Aids are discovery tools used to describe and provide access to our holdings. Finding aids include historical and biographical information about each collection in addition to inventories of their content. More information about our collections can be found on our website http://www.gettysburg.edu/special_collections/collections/.https://cupola.gettysburg.edu/findingaidsall/1066/thumbnail.jp

MS-076: George C. Wynkoop, 2nd Brigade, 2nd Division, Dept. of Pennsylvania

This collection consists of records from George Wynkoop’s service as a Brigadier General in the three month Pennsylvania Volunteers. Over three hundred pieces of correspondence, orders, forms, and daily reports make up the collection. The correspondence and reports come from a variety of locals at which the Department of Pennsylvania set up camp. Locations include Camp Scott and Camp Chambers, Pennsylvania, Hagerstown, Maryland and Harper’s Ferry, Virginia (Today West Virginia). Special Collections and College Archives Finding Aids are discovery tools used to describe and provide access to our holdings. Finding aids include historical and biographical information about each collection in addition to inventories of their content. More information about our collections can be found on our website http://www.gettysburg.edu/special_collections/collections/.https://cupola.gettysburg.edu/findingaidsall/1070/thumbnail.jp

MS-075: Henry W. Siebert, Company E, 16th Pennsylvania Volunteer Cavalry

The Henry W. Siebert journals, of which there are two, cover the years 1863 and 1865 respectively. The journals themselves are leather bound notebooks closed with straps, the whole measuring 3 inches by 6 inches. The 1863 volume numbers 90 pages, with entries for every day. The 1865 diary numbers 150 pages and has entries for January 1, 1865 through May 24, 1865. The entries are generally short in nature, not exceeding a paragraph in length. The text is normally limited to a discussion of the morning weather, general activity of the day and the geographic location reached by nightfall. A number of battles are mentioned, including Chancellorsville, Aldie, Upperville, Gettysburg, Petersburg and Appomattox. Special Collections and College Archives Finding Aids are discovery tools used to describe and provide access to our holdings. Finding aids include historical and biographical information about each collection in addition to inventories of their content. More information about our collections can be found on our website http://www.gettysburg.edu/special_collections/collections/.https://cupola.gettysburg.edu/findingaidsall/1069/thumbnail.jp

MS-074: Thomas B. McGaffick, Co. F, 101st Pennsylvania Volunteer Infantry

The letters of Thomas B. McGaffick, a corporal in Company F of the 101st Pennsylvania Volunteer Infantry range in date from January 19th, 1861 to February 11, 1863. The collection contains twenty two pieces of correspondence, including two fragments of letters along with a number of official documents relating to McGaffick’s discharge from the army. The letters are all addressed to members of Thomas’s family, including his sisters Belle and Mary, his brother Benjamin and his parents. The letters address a variety of subjects ranging from the rigors of army life to McGaffick’s constant battle with his own health. Thomas rarely received enough correspondence to keep him satisfied and was constantly after family members to write more. He described his thoughts on General McClellan, his desire to return home and the various women to whom he wrote during the conflict. Also of interest is McGaffick’s view towards the African Americans he encountered while in the south. “If I thought I was fighting to free the niggers I would go home and let and let Lincoln fight it out himself.” Special Collections and College Archives Finding Aids are discovery tools used to describe and provide access to our holdings. Finding aids include historical and biographical information about each collection in addition to inventories of their content. More information about our collections can be found on our website http://www.gettysburg.edu/special_collections/collections/.https://cupola.gettysburg.edu/findingaidsall/1068/thumbnail.jp

Theory and Simulations of Refractive Substructure in Resolved Scatter-Broadened Images

At radio wavelengths, scattering in the interstellar medium distorts the appearance of astronomical sources. Averaged over a scattering ensemble, the result is a blurred image of the source. However, Narayan & Goodman (1989) and Goodman & Narayan (1989) showed that for an incomplete average, scattering introduces refractive substructure in the image of a point source that is both persistent and wideband. We show that this substructure is quenched but not smoothed by an extended source. As a result, when the scatter-broadening is comparable to or exceeds the unscattered source size, the scattering can introduce spurious compact features into images. In addition, we derive efficient strategies to numerically compute realistic scattered images, and we present characteristic examples from simulations. Our results show that refractive substructure is an important consideration for ongoing missions at the highest angular resolutions, and we discuss specific implications for RadioAstron and the Event Horizon Telescope.Comment: Equation numbering in appendix now matches published version. Two minor typos correcte

Sub-Microarcsecond Astrometry and New Horizons in Relativistic Gravitational Physics

Attaining the limit of sub-microarcsecond optical resolution will completely revolutionize fundamental astrometry by merging it with relativistic gravitational physics. Beyond the sub-microarcsecond threshold, one will meet in the sky a new population of physical phenomena caused by primordial gravitational waves from early universe and/or different localized astronomical sources, space-time topological defects, moving gravitational lenses, time variability of gravitational fields of the solar system and binary stars, and many others. Adequate physical interpretation of these yet undetectable sub-microarcsecond phenomena can not be achieved on the ground of the "standard" post-Newtonian approach (PNA), which is valid only in the near-zone of astronomical objects having a time-dependent gravitational field. We describe a new, post-Minkowskian relativistic approach for modeling astrometric observations having sub-microarcsecond precision and briefly discuss the light-propagation effects caused by gravitational waves and other phenomena related to time-dependent gravitational fields. The domain of applicability of the PNA in relativistic space astrometry is explicitly outlined.Comment: 5 pages, the talk given at the IAU Colloquium 180 "Towards Models and Constants for Sub-Microarcsecond Astrometry", Washington DC, March 26 - April 2, 200

Size of the Vela Pulsar's Emission Region at 18 cm Wavelength

We present measurements of the linear diameter of the emission region of the Vela pulsar at observing wavelength lambda=18 cm. We infer the diameter as a function of pulse phase from the distribution of visibility on the Mopra-Tidbinbilla baseline. As we demonstrate, in the presence of strong scintillation, finite size of the emission region produces a characteristic W-shaped signature in the projection of the visibility distribution onto the real axis. This modification involves heightened probability density near the mean amplitude, decreased probability to either side, and a return to the zero-size distribution beyond. We observe this signature with high statistical significance, as compared with the best-fitting zero-size model, in many regions of pulse phase. We find that the equivalent full width at half maximum of the pulsar's emission region decreases from more than 400 km early in the pulse to near zero at the peak of the pulse, and then increases again to approximately 800 km near the trailing edge. We discuss possible systematic effects, and compare our work with previous results