On August 13, 1898, astronomers Gustav Witt and Auguste H.B. Charlois independently discovered an asteroid which would become a focal point of numerous studies throughout the next century, 433 Eros. Eros was the first near-Earth asteroid (NEA) to be discovered, crossing the orbit of Mars, and is amongst the largest NEAs in the solar system. 433 completes its orbit around the Sun every 1.76 years or 643 days and rotates on its axis once every 5.270 hours. Containing silicaceous materials, Eros is an S-type asteroid which is the most common type of asteroid found in the inner solar system. 
Many of the studies of Eros have involved the Harvard College Observatory (HCO) at their core. The first of these studies was undertaken in order to produce a more accurate ephemeris for Eros. An ephemeris is a model that predicts the position of an object in the sky at a certain time and location. The ephemeris of Eros would become crucial for a later study which made use of the information generated here to calculate the distance from the Earth to the Sun.
The ephemeris study of Eros was led by Seth Carlo Chandler and Williamina Fleming at the HCO, with the predetermined goal of having an accurate ephemeris for the measurements of the upcoming opposition project of 1901 (described in the next post). Chandler had created a very rough ephemeris of the path of Eros, but there was a very large degree of uncertainty in the predicted positions. As a result, astronomers would not know exactly what area of the sky to image when photographing Eros.  Fleming carried out an extensive analysis and examined over 1300 square degrees of data in plates by eye. For comparison, the entire sky is about 41000 square degrees, so Fleming analyzed about three percent of the entire sky. Eventually, 21 non-spectral plates of Eros were found, many of which were labeled with the asteroid and comparison stars used to measure its position. This allowed for a more precise ephemeris to be calculated. In this process, additional images of asteroids Flora and Nysa were found, and two new variable stars were discovered. Below are photographs of the plates and jackets of four plates that Fleming had found. These plates can still be found at the HCO today.
Additionally, Henry Norris Russell recalculated and further enhanced the ephemeris of Chandler one year later. His calculations combined those of Chandler and additional measurements taken by Washburn Observatory. This further refined the ephemeris of Eros. 
The ephemeris project in 1899 would prove to be an invaluable asset. Having the knowledge of the exact orbital properties of Eros would be required when refining the astronomical unit. This would become the next major project to feature this asteroid just one year later.
1. “Near-Earth Asteroid 433 Eros.” NASA, n.d. Web. 15 July 2013.
2. Russell, Henry Norris. “Elements and Ephemeris of (433) Eros” 1899AJ…..20….8R Page 8. The SAO/NASA Astrophysics Data System, 1899. Web. 15 July 2013.
3. Jones, Bessie Zaban, and Lyle Gifford Boyd. The Harvard College Observatory: The First Four Directorships, 1839-1919. Cambridge, MA: Harvard UP, 1971. Print. pp343-344.
4. Pickering, Edward Charles. “Witt’s Planet (433), DQ.” Witt’s Planet (433), DQ. The SAO/NASA Astrophysics Data System, 1899. Web. 12 July 2013.
5. Pickering, Edward Charles. “Early Observations of Eros (433).” Early Observations of Eros (433). The SAO/NASA Astrophysics Data System, 1905. Web. 28 July 2013.
6. Pickering, Edward Charles. “Witt’s Planet (433), DQ.” Witt’s Planet (433), DQ. The SAO/NASA Astrophysics Data System, 1899. Web. 12 July 2013.
7. Russell, Henry Norris. “Elements and Ephemeris of (433) Eros” 1899AJ…..20….8R Page 8. The SAO/NASA Astrophysics Data System, 1899. Web. 15 July 2013.