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“Andromeda galaxy actual size in Earth's sky”

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“Andromeda galaxy actual size? Yes. This image truly depicts what the night sky would look like if the Andromeda galaxy – the galaxy next door – were brighter. Original background shot of the moon by Stephen Rahn. Andromeda galaxy image via NASA. Composite photo by Tom Buckley-Houston. The composite showed up on Reddit a few years ago. Not convinced? Here’s a similar image via APOD.

“The image above shows how the neighboring Andromeda galaxy occupies about the width of six moon-diameters on our sky’s dome. But, of course, the galaxy isn’t nearly this bright. You need a dark sky to see it, and, even then, it’s a barely visible fuzzy patch of light. In order to appear as bright as in the image above, the Andromeda galaxy would need to be closer. If it were close enough to look so bright, it would appear even bigger on our sky’s dome. And that’s going to happen someday! The Andromeda galaxy is currently racing toward our Milky Way at a speed of about 70 miles (110 km) per second. Ultimately, the two galaxies will collide and merge.

“Normally, the news that the Milky Way and Andromeda are going to collide is not a very headline-causing piece of information, since it is due to take place in about 5 billion years. But, new research published in the peer-reviewed Astrophysical Journal in August this year reveals that the timeline has been revised: The collision has already started!

“That news about the Andromeda galaxy came from Project AMIGA, which uses the Hubble Space Telescope to look at the deep-space surroundings of the Andromeda galaxy. AMIGA stands for Absorption Map of Ionized Gas in Andromeda. NASA reported on this study earlier this year, calling it “the most comprehensive study of a halo surrounding a galaxy.”

“The Andromeda galaxy, our Milky Way and other galaxies all sit enshrouded in a large envelope – a so-called galactic halo – which consists of gas, dust and stray stars. The halos of galaxies are faint, so faint that detecting them is not an easy feat. These astronomers measured the size of the halo of the Andromeda galaxy by looking at how light from background quasars had been absorbed by it. They were surprised to find that the Andromeda galaxy’s halo stretches much, much farther out beyond the visible boundaries of the galaxy than previously known.

“In fact, it extends as far as half the distance to our Milky Way (1.3 million light-years) and even farther in other directions (up to 2 million light-years).

“Does this mean the halos of the Andromeda and Milky Way galaxies are touching?

“It turns out that, from our vantage point inside the Milky Way, we cannot easily measure the characteristics of our galaxy’s halo. However, because the two galaxies are so similar in size and appearance, scientists assume that the halo of the Milky Way would also be similar.

In other words, it’s the faint halos of the galaxies that indeed appear to have started to touch one another. Thus, in a manner of speaking, the collision between our two galaxies has already started.”

Click on the image copyright to continue reading at EarthSky.


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I haven't a clue. The page at the image copyright says:

"You need a dark sky to see it, and, even then, it’s a barely visible fuzzy patch of light. In order to appear as bright as in the image above, the Andromeda galaxy would need to be closer."


Would there ever gave been a time in Earth' s past when our sky would have been dark enough to see Andromeda like this?


Marilee, that's like saying you wish you could see the Milky Way. You can, kinda, but we're in the middle of it! Click on the image copyright; you might find something there to satisfy your wish.


The collision has already started... Well, I wish I COULD see it.


Yes, thanks.


Hope you figured it out, Donna. :-)

Wouldn't that be something to see in the night sky, Judy!?


How wondrous a site that would be.


My mind is chugging along trying to incorporate this into something that feels even close to sensible! My, my, my...