China
Africa
Explore chapters and articles related to this topic
Other Techniques
Published in C. R. Kitchin, Astrophysical Techniques, 2020
The declination of an object, δ, is its angular distance north or south of the equator. The right ascension, α, is its angular distance around from the meridian (or great circle) that passes through the vernal equinox and the poles, measured in the same direction as the solar motion (Figure 5.2). By convention, declination is measured from −90° to + 90° in degrees, arc-minutes and arcseconds and is positive to the north of the equator and negative to the south. Right ascension is measured from 0° to 360°, in units of hours, minutes and seconds of time where, at the equator, () 1 hour=15° () 1 minute=15′ () 1 second=15″
Introductory Material
Published in Ronald L. Snell, Stanley E. Kurtz, Jonathan M. Marr, Fundamentals of Radio Astronomy, 2019
Ronald L. Snell, Stanley E. Kurtz, Jonathan M. Marr
Right ascension (RA)Lines of longitude projected onto the sky define the coordinate called right ascension. However, because the Earth rotates on its axis, the projected lines of longitude shift with time relative to the celestial sphere, so the definition of right ascension is a little more complicated than declination. The fiducial point of right ascension is defined as the position of the Sun when it crosses the celestial equator in the Spring, a point on the sky known as the vernal equinox. Vernal equinox You may be familiar with the vernal equinox as the day in the year when the Sun crosses the equator, around March 21, but it is also defined as the position in the sky of the Sun at that time. A star's right ascension, then, is a measure of its angular distance eastward from the vernal equinox. One can compute, for any given moment in time, the angular offset (or time offset) between the fiducial line of right ascension and the fiducial line of longitude, and therefore we can locate any source on the sky. As a consequence of the rotation of the Earth relative to the sky, the values of right ascension are not measured in angle units, but are more conveniently given in units of time, with 24 hours representing a full circle at a fixed declination. Thus, 0 hours right ascension corresponds to 0°, 6 hours to 90°, 12 hours to 180° and 18 hours to 270°. Just as for time, each hour of right ascension is divided into 60 minutes and each minute is divided into 60 seconds. The use of time makes some sense, as the projected lines of longitude are constantly shifting with respect to the celestial sphere as the Earth rotates.
The Earth–Sun Relationship
Published in Matt Fajkus, Dason Whitsett, Architectural Science and the Sun, 2018
In astronomy, declination is one of two coordinates, along with right ascension, used in the equatorial coordinate system to describe the position of any celestial body. Declination corresponds with terrestrial latitude, measuring the angular distance of an object from the celestial equator, while right ascension corresponds to longitude, except that it is measured in hours, minutes, and seconds rather than degrees.
Kernelized Spectral Clustering based Conditional MapReduce function with big data
Published in International Journal of Computers and Applications, 2021
The Hipparcos star dataset is used to find the Hyades cluster members, and possibly Hyades supercluster members using the clustering process. It consists of an approximately spherical collection of hundreds of stars sharing the similar age, place of origin, chemical features, and movement through space. The Hipparcos star dataset contains 2719 Hipparcos stars (i.e. instances) which comprise several Hyades members with the selection criterion that the parallax lies between 20 and 25 ms (i.e. Hipparcos stars with distances 40–50 pc). The dataset consists of 9 attributes such as HIP (Hipparcos star number), Vmag (Visual band magnitude), RA (Right Ascension (degrees)), DE (Declination (degrees)), Plx i.e. Parallactic angle (mas = milliarcseconds). 1000/Plx gives the distance in parsecs (pc), pmRA (Proper motion in RA (mas/yr)),pmDE (Proper motion in DE (mas/yr)), e_Plx -Measurement error in Plx (mas), B-V (Color of star (mag)). These are the characteristics information of the Hipparcos star. By using this information, the Hipparcos star dataset finds the bright Hyades cluster members.
A new high-precision star map simulation model and experimental verification
Published in Journal of Modern Optics, 2021
Hongyuan Wang, Zhiqiang Yan, Xiaonan Mao, Bingwen Wang, Xiang Liu, Wen Kang
Navigation star map was obtained through observation in Shanghai late at night. The observation conditions were as follows: the optical axis of the camera pointed at (the right ascension: 101.6346°, the declination: 31.0510°), and the installation angle of the camera was 27.0438°. In order to verify the correctness of the simulation model, images of the same conditions are simulated. The ground measured and simulated star maps are shown in Figure 9. From the figure, it can be seen that the location distribution of the measured stars is consistent with that of the simulated stars, and the simulated stars are more than the measured stars, because measured stars are screened.
Monteiro da Rocha and the international debate in the 1760s on astronomical methods to find the longitude at sea: his proposals and criticisms to Lacaille’s lunar-distance method
Published in Annals of Science, 2022
Fernando B. Figueiredo, Guy Boistel
Monteiro da Rocha is perfectly aware of the necessity to have astronomical ephemeris with enough accuracy to implement the astronomical solution. The ‘Ephemeride Nautica’ imagined by him gave the Moon's celestial longitude tabulated in 4-4 hours for the meridian of Lisbon68 (Pingré gave the Moon's right ascension, and Lacaille the true lunar distance). The astronomical data provided are the longitude, right ascension and declination of the Sun; and the longitude, right ascension, and declination of the Moon, its horizontal and vertical parallax, and its half-diameter. The ‘Ephemeride Nautica’ also provided the mean longitude and the equation of time.