NIGHT SKIES
So why do we see the same constellations for all our lives, and why do they never change? While we’re orbiting the sun and the sun is orbiting around our home Milky Way galaxy, shouldn’t we see different constellations as we move around the galaxy center? -- Asking for a friend.
No grasshopper, it’s just not that simple. We are indeed orbiting the sun while the sun itself is moving through the galaxy.
The Earth’s orbit around the sun is negligible in this calculation. It’s just not large enough to matter. Our sun lies 25,700 light years from the center of the galaxy. Our solar system, including the sun, is moving at 143 miles per second relative to the Milky Way’s nucleus which defines the center of our galaxy, and the other suns (stars) are moving at comparable speeds.
At this rate, our solar system completes one orbit around the galaxy every 225 million years. We humans on average live 70 to 80 years if we’re lucky. We’re just alive for a split second of time in relationship to astronomical distances, even within our own galaxy.
Imagine being stuck on flypaper. In our individual lifetimes, we’re stuck on flypaper as surely as a fly. Now to complicate things, each individual star (100 billion stars in the Milky Way) is going on a slightly different path around the galaxy’s center, sometimes greatly different.
So over time yes, all the nearer stars that make up our constellations will change. But without much faster than light travel, we’ll never notice it. They’re just too far away, even the closest of them, to be noticeable to the naked eye.
As a consequence, the star patterns we observe today are essentially the same as were seen at the beginning of recorded human history.
Throughout a human lifetime, the constellations remain the same. However, if we lived for tens of thousands of years, we would eventually notice alterations in these patterns. Also, if we could travel to distant stars faster than light travel, when we popped out at the other side many of our constellations might be changed. A few would remain the same. That would be something to see but it also might be quite disconcerting. Over very long periods of time (millions of years) the stars comprising the constellations we observe today will move out of our view. As the sun moves into distant regions of the galaxy, other stars will become visible and new constellations will adorn the sky. Of course, most of the stars we see in the sky now will remain in view for tens or hundreds of thousands of years.
That’s the astronomy lesson for this month.
The week of May 15 through May 20 can be thought of as “new moon week” as the moon won’t be in the pre midnight sky all week and the actual new moon (not visible all night) is Friday May 19th and 20th.
This would be an excellent time to pack up the tent and go to a state park. If the kiddos are still in school, make it just the weekend of 19th through 21st. Obviously take your small telescope or binoculars and lie outside just gazing up at the magnificent sky. Take some Milky Way photos with your cell phone.
On the nights of May 22nd thru the 24th, look west shortly after dark and watch the moon pass upwards near bright Venus. This will also be a cell phone or SLR camera opportunity. Each night the crescent moon will be rising higher and passing Venus in the sky from our perspective.
And now I have a children’s book you will want to give to a grandchild or your own child. It’s called Clipper, Cosmos, and Children, Finding the Eureka Moment by David H. Levy. You can read it cover to cover in one afternoon. It has everything, a magic dog and telescope, heroes, astronomy, astrophysics, a good story, and some philosophy. There are great drawings by Joan Rosenthal. This is a book you would want to read to a child, or an older child would want to read for themselves. 117 pages, paperback. RJI Publishing. It’s also available on Amazon if you enter David H. Levy.
And finally, I’ve attached a first quarter moon image that I took on Feb 27, 2023 from my backyard. The moon can be very photogenic and an easy target for the smallest of telescopes. You can get good photos by just holding up your cell phone to the eyepiece. This was taken through my Unistellar eQuinox telescope, .09 milliseconds.
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