We are currently in the vanguard of the inner solar system!

Miscellaneous and Personal Stuff I Must Share
1

… if I have worked this out correctly. Even if I have, this will be simplistic, all figures are very approximate and much of this won’t apply any more in a few months. But the point is that wherever you are in the next few weeks, at midnight you can face the direction the whole solar system is travelling, like Kate Winslett on the prow of the Titanic, with the sun and the other planets trailing in our (imaginary) wake.

This is inspired by an animation I saw somewhere, probably linked from here, that showed the way the solar system moves through the Milky Way. The sun moves along at a steady pace, surrounded by its planet outriders. The planets are constantly overtaking the sun or falling back behind it - in the context of the galaxy the planets all follow wavy lines rather than the ellipses we are used to seeing depicted.

So as the the solar system orbits the centre of the Milky Way it is moving in the direction of the constellation Hercules, with its speed relative to the whole galaxy being perhaps about 225km/sec. The exact spot we are approaching has a right ascension of 18h 28m. Today the sun is at 05h 30m. The earth is therefore between the sun and Hercules (it will be almost a straight line in a couple of weeks).

This means that having been racing ahead of the sun for the past few months, we are almost directly in front of it in our mutual journey round the galaxy. Soon we will move out to the left and begin to fall back behind the sun again. But just now, at around midnight wherever you are, if you look south/north/straight up towards the 30° north line in the sky, you will be facing the direction of travel of the whole solar system.

What’s more is that along with Saturn way out to our left*, we are the leading planets (in this diagram we are all collectively travelling towards the bottom of the page). Pluto is ahead of us and most of the other planets are strung out to the left* of the sun.

The sun will get to the general area where we now are in the galaxy in about a week, by which time we will of course have moved on. The front edge of the Kuiper belt is perhaps a year ahead of us. It will take the earth thousands of years to get to where the front of the Oort cloud currently is. The back of the Oort cloud will be about the same distance behind us.

*right if you’re south of 30° north.

2

Very cool. Now we just need @neiltyson to come back and comment on this. :slight_smile:

3

Realistically, the inner planets have lapped us and are just about to lap us again, like Captain America.

4

When I say “inner solar system” here I meant the bits that are inside the Kuiper belt, sorry if that’s misleading. I’m not talking about a race round the sun with Venus and Mercury - for the purpose of this thread, they will always be behind the earth every June in our journey around the galaxy (in December they will be in front of us).

5

Yeah, but those planets suck. EARTH RULES!

6

Sorry if I’ve annoyed any one by not capitalising Earth in this thread :grinning:

7

I’m bumping this partly because the actual moment I was talking about will be in the next day or so, but also to correct the erroneous parts of my OP.

We are indeed about cease moving ahead of the sun in its orbit around the galaxy and start falling behind it, if I’ve understood the stuff about the solar apex correctly. However it isn’t as exciting as I first thought. I had unthinkingly assumed that the orbit of the solar system around the galaxy was on roughly the same plane as the orbit of the planets round the sun. It isn’t, the difference is about 60°. In a way that’s cooler, but it it does mean I was wrong about the Sun moving into the space the Earth had previously occupied. We are still a little bit ahead of the Sun but we’re not directly ahead of it and never will be, I was similarly wrong about the Kuiper belt.

In the second of the links I gave above I failed to press the option for a scale view of the solar system, which would have shown that Saturn is a long way ahead of us, and probably Neptune too.

But anyway, we do continue to whirl around the galaxy at a speed that is much faster than that of our orbit round the sun. If you’re far enough north of the Arctic Circle just now, at around 1am, you can look south and up a bit. As you tilt your head, the Sun will be above and behind you (hopefully the sky isn’t cloudy). Imagine the Sun speeding along in the direction you’re looking, with us below and slightly in front of it like a tiny outrider.