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<blockquote data-quote="Umbran" data-source="post: 6710782" data-attributes="member: 177">There is a phrase often used by physicists (and other hard sciences): &quot;...to first approximation...&quot;&nbsp; It is a useful concept here.There's an actual technical definition (see Wikipedia, &quot;<a href="https://en.wikipedia.org/wiki/Orders_of_approximation" target="_blank">Orders of Approximation</a>&quot;) , but, for our purposes, it means, &quot;Taking the strongest factor into account, and leaving out the smaller factors&quot;.A *lot* of what I say here is really to first approximation, because the secondary (and tertiary, and so on) factors will often seem like major complications, that will typically get in the way of understanding the base concept.&nbsp;&nbsp; If Freyar and I have disagreements, it is usually that I think he's jumped on to secondary effects before we've established that folks understand the primary ones. <img src="https://cdn.jsdelivr.net/joypixels/assets/8.0/png/unicode/64/1f642.png" class="smilie smilie--emoji" loading="lazy" width="64" height="64" alt=":)" title="Smile&nbsp; &nbsp; :)"&nbsp; data-smilie="1"data-shortname=":)" />So, to first approximation, as compared to the speed of light, the Earth can be considered stationary. Then, you can lay upon that the motions of the sun through the galaxy, and the Earth around the Sun.&nbsp; Note that, on long average (say, over a trip that will take the Earth around the Sun 90 times) the Earth's motion around the Sun won't mean much, as it is pretty much a closed loop - over the long haul, that loop will average out to almost zero.&nbsp; And yes, the Sun moves a bit, but you already had that in mind.&nbsp; The way you drew it, the Sun's motion was pretty much perpendicular to the ship's motion, which also decreases the impact of that motion to the main picture.</blockquote>

[QUOTE="Umbran, post: 6710782, member: 177"] There is a phrase often used by physicists (and other hard sciences): "...to first approximation..." It is a useful concept here. There's an actual technical definition (see Wikipedia, "[url=https://en.wikipedia.org/wiki/Orders_of_approximation]Orders of Approximation[/url]") , but, for our purposes, it means, "Taking the strongest factor into account, and leaving out the smaller factors". A *lot* of what I say here is really to first approximation, because the secondary (and tertiary, and so on) factors will often seem like major complications, that will typically get in the way of understanding the base concept. If Freyar and I have disagreements, it is usually that I think he's jumped on to secondary effects before we've established that folks understand the primary ones. :) So, to first approximation, as compared to the speed of light, the Earth can be considered stationary. Then, you can lay upon that the motions of the sun through the galaxy, and the Earth around the Sun. Note that, on long average (say, over a trip that will take the Earth around the Sun 90 times) the Earth's motion around the Sun won't mean much, as it is pretty much a closed loop - over the long haul, that loop will average out to almost zero. And yes, the Sun moves a bit, but you already had that in mind. The way you drew it, the Sun's motion was pretty much perpendicular to the ship's motion, which also decreases the impact of that motion to the main picture. [/QUOTE]

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