Cosmic Chameleon: Galaxy’s Stunning Transformation by Hubble Filters

Spiral Galaxy NGC 1385

Hubble Space Telescope image of the barred spiral galaxy NGC 1385, located about 30 million light-years away. Credit: ESA/Hubble & NASA, R. Chandar, J. Lee and the PHANGS-HST team

The barred spiral galaxy NGC 1385 appears in two strikingly different Hubble telescope images, attributed to the use of various specialized filters.

This luminous tangle of stars and dust is the barred spiral galaxy NGC 1385, which is located approximately 30 million light-years from Earth. The same galaxy was the subject of another Hubble Picture of the Week (see image below), but the two images are notably different. This more recent image has far more pinkish-red and umber shades, whereas the former image was dominated by cool blues. This chromatic variation is not just a creative choice, but also a technical one, made in order to represent the different number and type of filters used to collect the data that were used to make the respective images.

Galaxy NGC 1385

Hubble Space Telescope image of spiral galaxy NGC 1385, located 68 million light-years away from Earth, in the constellation Fornax. Credit: ESA/Hubble & NASA, J. Lee and the PHANGS-HST Team

Understanding Telescope Imaging Techniques

It is understandable to be a bit confused as to how the same galaxy, imaged twice by the same telescope, could be represented so differently in two different images.

The reason is that — like all powerful telescopes used by professional astronomers for scientific research — Hubble is equipped with a range of filters. These highly specialized components have little similarity to filters used on social media: those software-powered filters are added after the image has been taken, and cause information to be lost from the image as certain colors are exaggerated or reduced for aesthetic effect.

In contrast, telescope filters are pieces of physical hardware that only allow very specific wavelengths of light to enter the telescope as the data are being collected. This does cause light to be lost, but means that astronomers can probe extremely specific parts of the electromagnetic spectrum. This is very useful for a number of reasons; for example, physical processes within certain elements emit light at very specific wavelengths, and filters can be optimized to these wavelengths.

Comparing Images of NGC 1385

Take a look at this week’s image and the earlier image of NGC 1385. What are the differences? Can you see the extra detail (due to extra filters being used) in this week’s image?

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