Hubble Space Telescope image featuring spiral galaxies NGC 1356, LEDA 467699, LEDA 95415, and IC 1947.Credits: ESA/Hubble & NASA, J. Dalcanton, Dark Energy Survey/DOE/FNAL/NOIRLab/NSF/AURA, Acknowledgments: L. Schatz
This week’s Hubble photos feature an abundance of spiral galaxies. The large, prominent spiral galaxy on the right side of the image is NGC 1356. Two noticeably smaller spiral galaxies on either side of it are LEDA 467699 (above it) and LEDA 95415 (very close to its left), respectively. And finally, IC 1947 is located along the left side of the image.
This image is a very interesting example of how difficult it is to determine whether two galaxies are actually close together, or whether it just appears that way from our vantage point on Earth. A quick look at this image would lead you to believe that NGC 1356, LEDA 467699, and LEDA 95415 are all nearby, while IC 1947 is much further away. However, it is important to remember that such two-dimensional images only show angular separation, or how objects are spread out across the sphere of the night sky. What they cannot express is the distance between the object and the Earth.
For example, NGC 1356 and LEDA 95415 appear so close that they must definitely be interacting, but the former is about 550 million light-years from Earth and the latter about 840 million light-years from Earth. It’s far away. 300 million light years Separation between them. This also means that LEDA 95415 is unlikely to be as much smaller than NGC 1356 as it appears.
Meanwhile, although NGC 1356 and IC 1947 appear to be relatively far apart in this image, IC 1947 is only about 500 million light-years from Earth. In fact, it is a much closer neighbor in three-dimensional space than NGC 1356 and LEDA 95415, since the apparent angular distance between them in this image is less than 400,000 light years.