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Founded January 1970
Julian Date: 24591152.16
2020-2021: XXXV
THE DAILY ASTRONOMER
Thursday, October 29, 2020
Remote Planetarium 113: Nearby Superclusters
Unfathomable!
Here we are on Earth:
A terrestrial planet more than 90 million miles away from its parent star. From a cosmic perspective, Earth is negligibly small. Yet, to us it is inconceivably huge. How huge? If hollowed out, 2,000,000,000,000,000,000,000 people could fit inside it. That number is approximately equal to 256,410,256,410 times the current world population of 7.8 billion!
When compared to the Sun, Earth doesn't seem quite as immense:
1.2 million Earths could fit inside the Sun.
The Sun is but one of 300 billion stars within the Milky Way Galaxy. A number that is so large as to be beyond intuition and therefore unimpressive. However, if we drew a scale model map of the Milky Way Galaxy that could cover the entire North American continent, our entire solar system -Sun included, of course- would fit neatly inside a coffee cup. The Milky Way Galaxy, itself, is but a part of the Local Group of Galaxies: a collection consisting of more than 80 galaxies, most of which are dwarfs. The Andromeda and Milky Way Galaxies are the two largest members.
The Local Group comprises just a small part of the Virgo Supercluster:
The volume of the Virgo Supercluster is 7000 that of the Local Group and 100 billion times that of the Milky Way Galaxy! We can see that at this level, our galaxy becomes comparatively minuscule.
Now, we learn that our Universe contains 10 million Superclusters! Yet again we encounter an intuition-defying number. Think of that value this way: Ten million minutes equals approximately 19 years! Below we see an image of the local Superclusters: those in "close" proximity to the Virgo Supercluster of which we are a part.
Each of those "smudges" contains a collection of groups consisting of galaxies. At this level, even the vast Milky Way appears to be little more than a pinpoint light source.
Notice that the vast "voids" separate Superclusters. As their name suggests, these voids consist of large swaths of emptiness, save for errant stars and planets that might have been expelled from their host galaxies. Yet, these isolated bodies are likely few and far between. Mostly, innumerable light years of nothing keep Superclusters apart.
Superclusters generally consist of dozens of galaxy groups, each consisting of 10,000,000,000,000 - 100,000,000,000,000 solar masses worth of material. Superclusters tend to be distributed over millions of light years of space.
The next question, which we will address next week, is how can astronomers determine the sizes and distances of these structures that are so massive, immense, and far away? After all, we are confined to this minuscule planet within a small spur inside a galaxy that is mote-like when compared to its Supercluster. As we shall learn, the techniques astronomers use to make these determinations are of relatively recent origin.
More on the Cosmic Distance Ladder next week.