Milky Way Galaxy seen over Auxiliary Telescope

This image captures the route from the Residencia — the guesthouse for visitors to ESO's Paranal Observatory— to the breathtaking heart of the Milky Way, which covers the entire night sky.

The site shown here is Cerro Paranal, home to ESO's Very Large Telescope (VLT), a telescope comprising four 8.2-metre Unit Telescopes. The VLT can also act as an interferometer in the form of the appropriately-named VLT Interferometer, or VLTI, by gathering additional light from four smaller Auxiliary Telescopes, which can be independently moved around and placed in different configurations. One of these Auxiliary Telescopes is shown in this image, gazing at the sky with its dome wide open.

The road from the observatory to the Residencia appears as a shining thread, weaving amongst the rocky outcrops and hills of the desert environment. The yellow glow is caused by dim security lights — the street lighting is kept to a minimum in order to avoid unnecessary light pollution.

Image Credit: ESO/B. Tafreshi
Explanation from: https://www.eso.org/public/images/potw1732a/

Dwarf Galaxy NGC 5949

The subject of this NASA/ESA Hubble Space Telescope image is a dwarf galaxy named NGC 5949. Thanks to its proximity to Earth — it sits at a distance of around 44 million light-years from us, placing it within the Milky Way’s cosmic neighbourhood — NGC 5949 is a perfect target for astronomers to study dwarf galaxies.

With a mass of about a hundredth that of the Milky Way, NGC 5949 is a relatively bulky example of a dwarf galaxy. Its classification as a dwarf is due to its relatively small number of constituent stars, but the galaxy’s loosely-bound spiral arms also place it in the category of barred spirals. This structure is just visible in this image, which shows the galaxy as a bright yet ill-defined pinwheel. Despite its small proportions, NGC 5949’s proximity has meant that its light can be picked up by fairly small telescopes, something that facilitated its discovery by the astronomer William Herschel in 1801.

Astronomers have run into several cosmological quandaries when it comes to dwarf galaxies like NGC 5949. For example, the distribution of dark matter within dwarfs is quite puzzling (the “cuspy halo” problem), and our simulations of the Universe predict that there should be many more dwarf galaxies than we see around us (the “missing satellites” problem).

Image Credit: ESA/Hubble & NASA
Explanation from: https://www.spacetelescope.org/images/potw1732a/

Prometheus and F Ring

The thin sliver of Saturn's moon Prometheus lurks near ghostly structures in Saturn's narrow F ring in this view from NASA's Cassini spacecraft. Many of the narrow ring's faint and wispy features result from its gravitational interactions with Prometheus (86 kilometers, or 53 miles across).

Most of the small moon's surface is in darkness due to the viewing geometry here. Cassini was positioned behind Saturn and Prometheus with respect to the sun, looking toward the moon's dark side and just a bit of the moon's sunlit northern hemisphere.

Also visible here is a distinct difference in brightness between the outermost section of Saturn's A ring (left of center) and rest of the ring, interior to the Keeler Gap (lower left).

This view looks toward the sunlit side of the rings from about 13 degrees above the ring plane. The image was taken in visible light with the Cassini spacecraft narrow-angle camera on May 13, 2017.

The view was acquired at a distance of approximately 680,000 miles (1.1 million kilometers) from Saturn. Image scale is 4 miles (6 kilometers) per pixel.

Image Credit: NASA/JPL-Caltech/Space Science Institute
Explanation from: https://photojournal.jpl.nasa.gov/catalog/PIA21340