Same galaxy, different filters

This luminous tangle of stars and dust is the barred spiral galaxy NGC 1385, that lies about 30 million light-years from Earth. The same galaxy was the subject of another Hubble Picture of the Week, 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.

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 specialised 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 colours 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 optimised to these wavelengths.

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?

[Image Description: A spiral galaxy. It has several arms that are mixed together and an overall oval shape. The centre of the galaxy glows brightly. There are bright pink patches and filaments of dark red dust spread across the centre.]

Links

• Pan of Same galaxy, different filters