Schönen Gründonnerstag!
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This image shows a globular cluster known as NGC 1651. Like the object in another recent Picture of the Week, it is located about 162 000 light-years away in the largest and brightest of the Milky Way’s satellite galaxies, the Large Magellanic Cloud (LMC). A notable feature of this image is that the globular cluster almost fills the entire image, even though globular clusters are only about 10 to 300 light-years in diameter (NGC 1651 has a diameter of roughly 120 light-years). In contrast, there are numerous Hubble Pictures of the Week that feature entire galaxies — which can be tens or hundreds of millions of light-years in diameter — that also more or less fill the whole image.
A common misconception is that Hubble and other large telescopes manage to observe wildly differently sized celestial objects by zooming in on them, as one would with a specialised camera here on Earth. However, whilst small telescopes might have the option to zoom in and out to a certain extent, large telescopes do not. Each telescope’s instrument has a fixed ‘field of view’ (the size of the region of sky that it can observe in a single observation). For example, the ultraviolet/visible light channel of Hubble’s Wide Field Camera 3 (WFC3), the channel and instrument that were used to collect the data used in this image, has a field of view roughly one twelfth the diameter of the Moon as seen from Earth. Whenever WFC3 makes an observation, that is the size of the region of sky that it can observe.
The reason that Hubble can observe objects of such wildly different sizes is two-fold. Firstly, the distance to an object will determine how big it appears to be from Earth, so entire galaxies that are relatively far away might take up the same amount of space in the sky as a globular cluster like NGC 1651 that is relatively close by. In fact, there's a distant spiral galaxy lurking in this image, directly left of the cluster — though undoubtedly much larger than this star cluster, it appears small enough here to blend in with foreground stars! Secondly, multiple images spanning different parts of the sky can be mosaiced together to create single images of objects that are too big for Hubble’s field of view. This is a very complex task and is not typically done for Pictures of the Week, but it has been done for some of Hubble’s most iconic images.
[Image Description: A spherical collection of stars, which fills the whole view. The stars merge into a bright, bluish core in the centre, and form a sparse band around that out to the edges of the image. A few stars lie in front of the cluster, with visible diffraction spikes. The background is dark black.]
Credits: ESA/Hubble & NASA, L. Girardi, F. Niederhofer; CC BY 4.0
Tags: NGC 1651 ESA European Space Agency Space Universe Cosmos Space Science Science Space Technology Tech Technology HST Hubble Space Telescope Galaxy Supernova NASA Creative Commons Stars Star Globular Cluster
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The Copernicus Sentinel-3 mission takes us over northern Brazil, where the Amazon River meets the Atlantic Ocean.
Originating in the Andes, the Amazon River flows east, traversing six South American countries before reaching the northeast coast of Brazil, where it empties into the Atlantic. The sediment-laden river appears brown as it flows to the open ocean in the upper centre of the image.
The coast is surrounded by a muddy-brownish plume of suspended sediment, carried from upstream to the maze of channels constituting the 270-km-wide mouth of the Amazon. Discharge from the Amazon River, the Amazon plume, accounts for around 20% of the global input of freshwater into the ocean from Earth's land surfaces.
The Amazon has over 1000 tributaries, some of which are visible as thin, winding lines entering the river from the south, including the Tapajos River to the west and, further downstream, the Xingu River. The dark colour of these sediment-poor tributaries contrasts with the brownish sediment-rich Amazon waters.
The Tapajós-Xingu area is an important moist forest ecoregion. However, the Transamazon Highway, discernible as a brown line traversing this area, has spurred urbanisation.
The colour of the land varies, ranging from the deep green of dense, untouched vegetation to various tones of brown, highlighting the contrast between the rainforest and sprawling cultivation ̶ the fishbone-like patterns particularly visible along the highway.
Light green hues across the image denote agricultural areas, which were once covered by rainforest. The somewhat geometric shapes, which appear dark green and brown, result from forest clear-cutting.
Rainforests worldwide are disappearing at an alarming rate, a matter of great concern owing to their pivotal role in the global climate, and their status as habitats for a wide range of plants, animals and insects.
With their unique view from space, Earth observation satellites like Copernicus Sentinel-3 are instrumental in highlighting the vulnerability of rainforests by documenting, on a large scale, the extent and damage due to deforestation, particularly in remote regions.
Credits: contains modified Copernicus Sentinel data (2022), processed by ESA; CC BY-SA 3.0 IGO
Tags: Amazon plume Amazon River Brazil South America Atlantic Ocean Tapajos River Xingu River Transamazon Highway Rainforests Sentinel-3 ESA European Space Agency Space Space Technology Earth from Space Observing the Earth Earth Observation Earth Explorer Satellite image Sentinel Copernicus
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An AI generated image. Με Τεχνητή Νοημοσύνη.
March 29, 2024.
Thanassis Fournarakos - Θανάσης Φουρναράκος
Professional Photographer, Athens, Greece
(retired in 2011, born in 1946).
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None of my images may be downloaded, copied, reproduced, manipulated or used on websites, blogs or other media without my explicit written permission. THANK YOU!
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