NASA Astronomy Picture of the Day 2015 May 29

Saturn at Opposition 

Telescopic observers on Earth have been treated to spectacular views of Saturn lately as the ringed planet reached its 2015 opposition on May 23 at 0200 UT. Of course opposition means opposite the Sun in Earth’s sky. So near opposition Saturn is up all night, at its closest and brightest for the year. These sharp images taken within hours of the Sun-Earth-Saturn alignment also show the strong brightening of Saturn’s rings known as the opposition surge or the Seeliger Effect. Directly illuminated, the ring’s icy particles cast no shadows and strongly backscatter sunlight toward planet Earth, creating the dramatic surge in brightness. Saturn currently stands in the sky not far from bright Antares, alpha star of the constellation Sagittarius.

sun & moon, photographed by sdo, 30th january 2014.

an eclipse of the sun by the moon visible only from sdo, created by the alignment of their orbits. and, for good measure, a solar flare (left).

this sequence of 28 frames (photographed over 7 hours) combines images of two wavelengths, for reasons that i no longer clearly recall. this idiosyncratic postprocessing has, however, revealed some interesting textures of the image sensor.

image credit: nasa/sdo, aia/eve/hmi. animation: ageofdestruction.

Galactic onion

The glowing object in this image is an elliptical galaxy called NGC 3923. It is located over 90 million light-years away in the constellation of Hydra.

NGC 3923 is an example of a shell galaxy where the stars in its halo are arranged in layers.

Finding concentric shells of stars enclosing a galaxy is quite common and is observed in many elliptical galaxies. In fact, every tenth elliptical galaxy exhibits this onion-like structure, which has never been observed in spiral galaxies. The shell-like structures are thought to develop as a consequence of galactic cannibalism, when a larger galaxy ingests a smaller companion. As the two centres approach, they initially oscillate about a common centre, and this oscillation ripples outwards forming the shells of stars just as ripples on a pond spread when the surface is disturbed.

NGC 3923 has over twenty shells, with only a few of the outer ones visible in this image and its shells are much more subtle than those of other shell galaxies. The shells of this galaxy are also interestingly symmetrical, while other shell galaxies are more skewed.

Credit: ESA/Hubble & NASA
Acknowledgement: Judy Schmidt


     Blue Aurorae in Mars’ Sky Visible to the Naked Eye

For the first time, an international team of scientists from NASA, the Institute of Planetology and Astrophysics of Grenoble (IPAG), the European Space Agency and Aalto University in Finland, have predicted that colorful, glowing aurorae can be seen by the naked eye on a terrestrial planet other than Earth — Mars.

Visible Martian aurorae seemed possible after the SPICAM imaging instrument on-board the ESA satellite Mars Express spotted aurorae from space in 2005. Those observations were confirmed in March 2015 by the NASA-led MAVEN mission, which completed 1,000 orbits around the red planet on April 6, 2015.

Through laboratory experiments and a physical numerical model developed at NASA and IPAG, the study shows that, on Mars, aurorae also occur in the visible range. The most intense color is deep blue. As on Earth, green and red colors are also present. Several times during a solar cycle, after intense solar eruptions, these lights are bright enough to be seen with the naked eye.

Read more.

Pic: The Planeterella sphere simulates a magnetized planet with an atmosphere of CO2 and bombarded by the solar wind. Blue aurorae develop according to its magnetic field configuration.

Credits: D. Bernard/IPAG — CNRS

Mariner 9, the first spacecraft to orbit another planet, was launched en route to Mars on this day in 1971.

Mariner 9 completely changed our thoughts regarding Mars. Its cameras examined major features including Mars’ polar caps, the Valles Marineris canyon, and moons Phobos and Deimos while also noticing evidence of flowing water in Mars’ ancient past.

Learn more about Mariner 9 here:

Show your support for NASA’s continued exploration of Mars by writing Congress today: