This image of NGC 1651, a globular cluster in the Large Magellanic Cloud, exemplifies how celestial items of varying sizes appear in Hubbles images due to its set field of view and the objects range from Earth Credit: ESA/Hubble & & NASA, L. Girardi, F. NiederhoferHubble captures varied cosmic scales, from the close globular cluster NGC 1651 to distant galaxies, using its fixed observational scope and mosaicing when necessary.This Hubble Space Telescope image reveals a globular cluster called NGC 1651. Like the item in another recent Picture of the Week, it lies about 162,000 light-years away in the biggest and brightest of the Milky Ways satellite galaxies, the Large Magellanic Cloud (LMC). A significant feature of this image is that the globular cluster nearly fills the whole image, although globular clusters are just about 10 to 300 light-years in size (NGC 1651 has a size of roughly 120 light-years). On the other hand, there are numerous Hubble Pictures of the Week that feature entire galaxies– which can be tens or hundreds of millions of light-years in size– that also more or less fill the entire image.Telescope Field of View ExplainedA typical misunderstanding is that Hubble and other big telescopes handle to observe hugely in a different way sized celestial items by zooming in on them, as one would with a specialized camera here on Earth. Whilst little telescopes might have the choice to zoom in and out to a specific extent, large telescopes do not. Each telescopes instrument has a fixed field of view (the size of the area of sky that it can observe in a single observation). The ultraviolet/visible light channel of Hubbles Wide Field Camera 3 (WFC3), the channel and instrument that were used to gather the data used in this image, has a field of view roughly one-twelfth the size of the Moon as seen from Earth. Whenever WFC3 makes an observation, that is the size of the area of sky that it can observe.Capturing Cosmic ScaleThe factor that Hubble can observe objects of such extremely different sizes is two-fold. The distance to a things will determine how big it appears to be from Earth, so entire galaxies that are reasonably far away might take up the same quantity of area in the sky as a globular cluster like NGC 1651 which is relatively close by.In fact, theres a far-off spiral galaxy hiding in this image, directly left of the cluster– though unquestionably much larger than this star cluster, it appears small enough here to mix in with foreground stars! Secondly, several images spanning different parts of the sky can be mosaiced together to produce single pictures of objects that are too huge for Hubbles field of view.This is an extremely complex job and is not typically provided for Pictures of the Week, however it has been provided for some of Hubbles the majority of renowned images.
