This "Hubble Image of the Week" shows an abundance of spiral galaxies: The large, prominent spiral galaxy on the right side of the image is NGC 1356; the two significantly smaller spiral galaxies on either side of it are LEDA467699 (above it) and LEDA95415 (very close to its left); and finally, IC 1947 is on the left side of the image.

Spiral galaxies NGC1356, LEDA467699, LEDA95415 and IC1947 photographed by the Hubble Space Telescope. Image credit: ESA/Hubble and NASA, J.Dalcanton, Dark Energy Survey/DOE/FNAL/NOIRLab/NSF/AURA, Credits: L.Shatz

This image is an interesting example of how challenging it can be to tell whether two galaxies are really close, or just appear to be close from our perspective here on Earth.

Taking a quick look at this image, you might think that NGC1356, LEDA467699, and LEDA95415 are all close neighbors, while IC1947 is more distant. However, what we need to know is that two-dimensional images like this can only show the angular interval, that is, the distribution of celestial objects in the night sky. What they cannot represent is the distance of the celestial objects from the earth.

For example, while NGC 1356 and LEDA 95415 appear so close that they must be interacting, the former is about 550 million light-years from Earth and the latter is about 840 million light-years away, making them a whopping 300 million light-years apart. This also means that LEDA95415 is likely to be far less small than NGC1356 looks like.

On the other hand, although NGC 1356 and IC 1947 appear to be separated by a relatively distant chasm in this image, IC 1947 is only about 500 million light-years away. In this image, they are angularly separated by less than 400,000 light-years, so they are actually much closer in three dimensions than NGC1356 and LEDA95415!

Compiled source: ScitechDaily