Home Directory Directory
Notes on how to use the galaxy directory
The writing style and language were adapted to English.
1st function: coordinates of the recommended image center. These coordinates often contain the object listed first in the 3rd column, so, for example, the coordinates of the 1st field of view (RA 0h 1m 20s) are the position of NGC 7803. If the addition Fc (Field Center) is written after the coordinates, there is no bright galaxy in the center of the image. Here, several objects should be well distributed in the picture. The coordinates were taken from the SIMBAD database and rounded up to 0.1s in RA and 1" in DEC. The author determined the FC coordinates.
2nd function: SIMBAD: Click on individual coordinates of the 1st column with the mouse, switch between SIMBAD and Aladin Lite (Interactive Aladin Lite view). The basic data for all available objects within a 10' radius of these coordinates are listed, in some cases over 3,000 of all classes (it will take some time). It is difficult to work with so many objects. This is occasionally cautioned by a "!" behind the coordinates. If you click on the SIMBAD page in the column of an object, another one opens with the available data for this object. There is also a variety of other catalog references below. This is important because the author often used shorter names than those primarily displayed by SIMBAD due to lack of space. However, many faint galaxies can only be identified with NED. Please note that the author hardly used any information from SIMBAD under "Object Data" (column six).
"best view" stands for the day of longest observability. This refers to the date on which the culmination of the recording field occurs at midnight. The time was determined approximately with a rotating star map.
1st function: It names and catalog designations of some bright and also particularly remotely identifiable objects in the recording field. Often these are shortened by slashes, e.g.: IC 1642/46, LEDA 4370/92 = IC 1642, IC 1646, LEDA 4370, LEDA 4392 or the catalog name is omitted for subsequent objects, e.g. LEDA 85298, 1298602, 3091891 = LEDA 85298, LEDA 1298602, LEDA 3091891.
According to the SIMBAD database, no PGC names were used. These have the same numbers as LEDA.
If there is an asterisk * at the end of an object name, it is (at least for the author) one of the more beautiful and interesting image fields and should be considered when making your selection. An asterisk within the object name indicates a bright star in the image field. If there is a superscript ᴺ at the end of an object name, this object is not listed in SIMBAD and is taken from NED.
2nd function: The object designations are provided with a link to the Digitized Sky Survey, where the relevant section of the sky can be viewed. The pictures are from the famous Palomar Sky Survey (POSS II) and were exposed on analog photo plates and later digitized. The recording instrument was the 48-inch Palomar Oschin-Schmidt telescope with 1220/1830/3050 mm (the opening of the Schmidt plate/mirror diameter/focal length, 1:2.5).
Additional information on the links of the 3rd column (Digitized Sky Survey): First is the color sensitivity of the displayed analog plate images, B = Blue, R = Red, and second is the angular size of the displayed image field in arc minutes.
Usual abbreviations for the constellations in which the field of view lies.
Under Object Data, you will find abbreviated information (see abbreviations) for mostly four to five galaxies, due to very limited by space. In the beginning, there is usually the angular distance and the rough compass direction (in italics) in which an object is located away from the center of the image (north is up and east is always left). Distances > 10´ were measured on the screen by the author and are less precise. Tip: For better orientation, align the image axes of your photos with the cardinal points. The object names (see column three) have been abbreviated as follows, for example: NGC 7806 = N..06, LEDA 1950019 = L..19, 6dFGS gJ203220.5-020828 = 6d..28.
The galaxy type usually follows in brackets (fine subdivision omitted for elliptical galaxies), the angular extent and the total brightness (V = Visual, B = Blue brightness, g = Green brightness - SDSS standard, λ 490 nm and in few cases R = Red brightness).
The galaxies are usually fainter in the blue between 0.6 and 1 magnitude than in the visual (color index). Assuming 0.8 mag, you will have a good starting point for the conversion.
Since the angular expansion, in connection with the total brightness, is linked to an isophotal limit, and the objects often appear much larger on POSS II or SDSS, the author has repeatedly tried to determine the angular sizes on the screen himself with Aladin Lite (superscript ᴬ = source author). This was also often due to missing data in the databases. The redshift z can be found behind the brightness, where known or feasible due to lack of space.
This was not given heliocentrically as usual. Why? The 3K background radiation is the universal inertial system in terms of spatial expansion. Thanks to accurate satellite measurements, we now know that we are moving at about 620 km/s in one direction against the 3K background radiation. The author, therefore, used corrected redshifts from NED in which this movement was eliminated. The hit probability of an approximately correct light travel time is statistically the most possible. Unfortunately, as a rule, we do not know the intrinsic velocity of the galaxies in space and only receive an estimate of the light travel time, in which we interpret z alone as the expansion of space. In dense galaxy clusters, however, the intrinsic velocity can reach up to 1,000 km/s. Uncertainty is extremely high, especially for nearby objects. Therefore, the author often used distance information from Wikipedia (there, z is mostly corrected for the galactic center).
space probes WMAP and Planck (H0 is obviously not a constant). Further parameters of the LT calculations were: matter density 0.27, vacuum energy density 0.73 and a flat universe.
If LT is behind a bracket, this light travel time is valid together for two galaxies listed above.
If you tend to take the light travel time as a given distance in light-years, please consider the following: In an accelerated expanding universe, the equation of light travel time and distance becomes more and more absurd with increasing redshift! The light travel time is ideally equal to the distance in light-years that the light has traveled to us. However, this is neither the distance of the object when the light started traveling, nor is it the distance today, nor is it the time a light signal would need to get there now. Only in the cosmological vicinity of our Milky Way (up to about z = 0.1, and a light travel time of about 1.2 billion years) this simplified view is acceptable, considering the uncertainties.
Messier, NGC and IC object specifications (type, angular size, brightness) are taken from the NGC/IC project (directory by Dr. Wolfgang Steinicke, March 2018/19). The 3K-corrected redshifts are taken from NED (with a few exceptions). Information on fainter objects, clusters and quasars is also taken from NED (NASA/IPAC Extragalactic Database), the world's largest extragalactic database.
Deviations from this were generally indicated by superscript letters (ˢ, ᴺ, ʷ, ᴬ, ᴾᴳᶜ, ᴺᴵ - see abbreviations).
The information about bright stars comes from SIMBAD (SIMBAD Astronomical Database - CDS Strasbourg).
Reference stars: Bright stars (>3mag) are used to help locate the recording coordinates. The ancient Greek letters used were occasionally written out in brackets.
The visual brightness of the reference stars (source: SIMBAD), ~ means variable star.
Spectral types of the reference stars (source: SIMBAD).
Coordinates of the reference stars (source: SIMBAD), rounded up to 0.1s in RA and to 1" in DEC.
translated by Raymond Romanos