Category: APOD

Globular clusters are aggregations of stars in a spherical shape. They are bound by their mutual gravity and have high star density towards their centers. These ancient star clusters orbit the center of galaxies.

Globular clusters are considered to be old because they mostly contain low mass stars. It is important to understand that large stars have much shorter lives than low mass stars do. Smaller stars burn their fuel more slowly than larger stars. Also, large mass stars emit more blue light than do smaller stars resulting in them appearing blue.

Blue stragglers are young large mass stars in globular clusters. Their much younger age is incompatible with the age of the host globular cluster.

Astronomers believe that blue stragglers are the result of the merger of smaller stars in the cores of globular clusters. The relatively high concentration of stars in the cores of globular clusters facilitates these mergers.

The globar cluster NGC 6752 is located approximately 13,000 light-years away in the direction of the constellation Pavo. The cluster is over 10 billion years old and is a companion of our Milky Way. It contains more than one hundred thousand stars in a sphere 100 light-years across.

NGC6752 and its blue straggles
NGC6752 and its blue straggles. Note the star in the top left of the cluster is located between Earth and the cluster (click photo for larger image).

Image source: Globular Star Cluster NGC 6752

While I will not be posting every APOD I do wish to post the ones that I find appealing. This one also relates to the recent post of the all sky Milky Way.

This image concentrates on the Milky Way towards the galactic centre. Much of the galactic center is obscured by the dark lanes visible in this image. These lanes are present due to great clouds of gas and dust being located between us and the galactic centre. These clouds form dark nebulae. When gas and dust are located near a large star emission nebulae form. There are many emission nebulae present in this image.

The constellations visible in this image include Sagittarius, Libra, Scorpius, Scutum, and Ophiuchus. Emission nebulae visible include M8, M16 and M20. An example of a dark nebula in this image is the Pipe Nebula. There are numerous open clusters visible on the galactic plan and the globular M22 at a slight angle to the galactic plane.

For an anotated version of this image see the APOD website. Click the image below for a larger version.

Source: The Annotated Galactic Center

Jupiter’s moon Io is the most geologically active body in the solar system. All the colouring visible in this image is the result of eruptions on this small moon. The colour is due to the presence of sulfur compounds.

It is thought that there could be as many as 300 active volcanoes on Io. It is estimated that these volcanoes eject enough material to cover the moons surface to a depth of 1 metre every century.

Prior to the flyby of Voyager 1 in 1979 it was thought that this moon would be a dead body with ancient cratering. We now know that Jupiter’s gravity has a great influence on Io. As the moon orbits it is slightly influenced by the planets other moons which does not allow the moon to become tidally looked with the planet. As a result the planet is subjected to tidal forces that cause heating in the moon’s interior. This drives the volcanism observed on Io.

Source: Astronomy Picture of the Day

This is a stunning image of the Milky Way! The image takes in the sky if you could temporarily remove the Earth or was at a good distance away from our planet. The image is the result of taking 3000 images of the night sky and stitching them together. Many features of the night sky that are too dim for the human eye to detect are represented in the image. Particularly evident are the dark regions associated with gas and dust in the plane of the Milky Way. The Large and Small Magellanic Clouds are also distictive in the image.

If you are interested in the details of how this image was produced there is a paper available on the Milky Way Panorama 2.0 website. The website has a zoomable image version of the map.

Source: Astronomy Picture of the Day; Axel Mellinger

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