Hubble’s latest image features galaxy SDSS J103512.07+461412.2 from the Sloan Digital Sky Survey. Unlike simpler naming systems from smaller catalogs, SDSS uses coordinates, providing both identification and precise location in one name.
This Hubble Picture of the Week includes the pithily-named galaxy SDSS J103512.07+461412.2, visible in the center of this image as a dispersed sweep of dust and stars with a denser, brighter core. SDSS J103512.07+461412.2 is located 23 million light-years from Earth in the constellation Ursa Major. The seemingly rambling name is because this galaxy was observed as part of the Sloan Digital Sky Survey (SDSS), a massive survey that began in 2000 with the aim of observing and cataloging vast numbers of astronomical objects. So far, it has recorded several hundred million astronomical objects.
A Brief History of Astronomical Catalogs
In the early days of astronomy catalogs, astronomers painstakingly recorded individual objects one by one. As an example, the Messier catalog includes only 110 objects, identified by the astronomer Charles Messier because they were all getting in the way of his comet-hunting efforts. As the Messier catalog is so limited, it is sufficient to simply refer to those objects as M1 to M110. In contrast, when a survey as massive in scope as the SDSS is involved, and when huge volumes of data need to be processed in an automated manner, the names assigned to objects need to be both longer, and more informative.
Decoding the SDSS Naming Convention
To that end, every SDSS object has a designation that follows the format of: ‘SDSS J’, followed by the right ascension (RA), and then the declination (Dec). RA and Dec define the position of an astronomical object in the night sky. RA is analogous to longitude here on Earth, whilst the Dec corresponds to latitude.
To be more exact, RA measures the longitudinal distance of an astronomical object from the point where the celestial equator (the mid-point between the north and south celestial poles) intersects with the ecliptic (the plane in which Earth orbits around the Sun).
The entire night sky is then carved into 24 slices, known as ‘hours’, measured eastwards from that starting point (which is designated as zero hour). This means that the RA can be expressed in ‘hours’, ‘minutes’ and ‘seconds’. Dec is the angle north or south of the celestial equator, and is expressed in degrees.
Thus, the SDSS J103512.07+461412.2 name simply tells us that the galaxy can be found 10 hours, 35 minutes, and 12 seconds east of the zero-hour point on the celestial equator, and just over 46 degrees to the north of the celestial equator. So that lengthy name is really an identifier and a detailed location in one!