NASA spent $16 billion on Hubble Space Telescope, it cannot even zoom

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New Delhi: The Hubble Space Telescope has captured an image of the globular cluster designated as NGC 1651, at a distance of 1,62,000 lightyears, located within the Large Magellanic Cloud (LMC), the largest and brightest of the satellite galaxies of the Milky Way. Globular clusters are made up of up to a million stars, all born around the same time from the same stellar nursery, or vast clouds of gas and dust.

Hubble has revolutionised the study of globular clusters

Hubble has revolutionised the study of such globular clusters, because these objects appear as a single point of light on ground-based telescopes, that are unable to resolve the individual stars because of atmospheric disturbances. Hubble is providing scientists with a window to understanding entire populations of stars, and through them, the history and evolution of galaxies. The stars within an globular cluster tend to stay together for billions of years, bound together by the influence of gravity. Stars in an open cluster, by contrast, drift apart over billions of years.

The Hubble Space Telescope cannot zoom

The globular cluster fills the entire image, even though such clusters measure only between 10 and 300 lightyears across. NGC 1651 has a diameter of about 120 lightyears. While consumer cameras and hobby telescopes have the ability to zoom into subjects, large flagship deep space observatories do not. They are designed with a fixed field of view. The ultraviolet and visible light channel of the wide field camera 3 (WFC3) used to capture the image above has a field of view about one twelfth the diameter of the Moon.

It is a common misconception that space telescopes investigate an object by zooming into them. Instead, the telescope merely turns to orient itself towards the target. If the subject extends beyond the field of view of the instrument, then multiple images can be stitched together in a mosaic. Yes, NASA does manipulate the images that it releases, but that is another story. Every time WFC3 makes an observation, it covers a particular fraction of the sky.

The reason that NGC 1651 fills the frame is its proximity to the Earth. Within the image, hiding among the foreground stars, is an entire spiral galaxy, which is much larger than the globular cluster. Hubble cannot zoom into that galaxy. The foreground stars are marked by diffraction spikes that appear over particularly bright and concentrated sources of light, and are caused by light interacting with the internal support structure of the instrument. The cross-shaped diffraction spikes can be considered as a signature of Hubble.

How much does Hubble cost?

When adjusted for inflation to 2021 prices, the Hubble Space Telescope mission has cost NASA $16 billion. The cost does not include the expenses of the servicing missions by the space shuttles, that have progressively upgraded and fixed errors with the deep space observatory. The Hubble Space Telescope mission officially began in 1977. The Hubble Space Telescope is expected to continue operations till 2030-2040.

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