13-04-2018 10:24 AM CEST
europeanspaceagency posted a photo:
The Copernicus Sentinel-2A satellite takes us over southern India to the capital of Telangana: Hyderabad.
Home to almost seven million people and covering about 650 sq km, Hyderabad is one of the largest metropolitan areas in India. It lies on the banks of the Musi River, which can be seen running across the middle of the image. Although steeped in history, this rapidly growing metropolis has become a hub of commerce and an international centre for information technology, earning it the nickname of Cyberabad.
Captured on 14 May 2017, the image has been processed to highlight the different features in and around the city. The yellow and browns show the built-up centre while the light greens in the surroundings show arid fields. The shades of darker green depict vegetation and areas covered by trees. Interestingly, the bright blue, which appears, for example, along the Musi River and near other water bodies, is also vegetation such as parkland and grass.
While several lakes can be seen in the image, they are gradually being lost. It has been said that the city once had 7000 lakes, but there are now only about 70 and they are being subjected to pollution as the city expands and develops. Even the city’s most famous lake, the heart-shaped Hussain Sagar, is blighted with pollution from agricultural and industrial waste and municipal sewage.
The two identical Copernicus Sentinel-2 satellites carry high-resolution cameras working in 13 spectral bands. Images from the mission can be used to monitor pollution in lakes, changes in vegetation and urban growth.
This image is featured on the Earth from Space video programme.
Credits: contains modified Copernicus Sentinel data (2017), processed by ESA, CC BY-SA 3.0 IGO
A colossal cluster
10-04-2018 11:38 AM CEST
europeanspaceagency posted a photo:
This NASA/ESA Hubble Space Telescope image shows a massive galaxy cluster glowing brightly in the darkness. Despite its beauty, this cluster bears the distinctly unpoetic name of PLCK_G308.3-20.2.
Galaxy clusters can contain thousands of galaxies all held together by the glue of gravity. At one point in time they were believed to be the largest structures in the Universe — until they were usurped in the 1980s by the discovery of superclusters, which typically contain dozens of galaxy clusters and groups and span hundreds of millions of light-years. However, clusters do have one thing to cling on to; superclusters are not held together by gravity, so galaxy clusters still retain the title of the biggest structures in the Universe bound by gravity.
One of the most interesting features of galaxy clusters is the stuff that permeates the space between the constituent galaxies: the intracluster medium (ICM). High temperatures are created in these spaces by smaller structures forming within the cluster. This results in the ICM being made up of plasma — ordinary matter in a superheated state. Most luminous matter in the cluster resides in the ICM, which is very luminous X-rays. However, the majority of the mass in a galaxy cluster exists in the form of non-luminous dark matter. Unlike plasma, dark matter is not made from ordinary matter such as protons, neutrons and electrons. It is a hypothesised substance thought to make up 80 % of the Universe’s mass, yet it has never been directly observed.
This image was taken by Hubble’s Advanced Camera for Surveys and Wide-Field Camera 3 as part of an observing programme called RELICS (Reionization Lensing Cluster Survey). RELICS imaged 41 massive galaxy clusters with the aim of finding the brightest distant galaxies for the forthcoming NASA/ESA/CSA James Webb Space Telescope (JWST) to study.
Credits: ESA/Hubble & NASA, RELICS