# Appearance of sun at geologic past

After origin of Earth ( 4.54 billion years ago ) to today; what are the changes through-which the sun undergone with time? , ( if seen from Earth. )

I'm doing some palaeobiology-landscape rendering; so I'm thinking if I want to add the sun in such pictures; should I draw it just like present day? Or the look/ appearance (colour, size, flames, position, halo etc) varied in observable amount through the geologic time-scale(precambrian-cambrian-ordovician-silurian-devonian-carboniferous-permian-triassic-jurassic-cretaceous-palaeogene-neogene etc). (the timescale terms provided just to hint the answerer the level of details may NOT to go )

Update: Here I attach a small version of geologic time table to indicate time ranges.

from here .

To see the entire chart; see international commission of stratigraphy charts

• Can you add some more astronomically-friendly information, like millions of years? recambrian-cambrian-ordovician-silurian-devonian-carboniferous-permian-triassic-jurassic-cretaceous-palaeogene-neogene is not so helpful. Also.... flames??? :) – uhoh Apr 20 '17 at 6:39
• @uhoh okay I'm editing the question. By "flame" I tried to mean was there solar storms , volcanoes etc that may be required? (don't know is there any term for that. In many cosmology-related popular-science books I've seen telescopic images of specialized stars that have radiating flame-like things)... but no idea if there any term for it. Will provide an image when I'll found out the book. – Always Confused Apr 20 '17 at 6:46
• OK thanks for the edit, it's a big improvement. Are you talking about illustrations of the appearance as it might be from the Earth's surface with something similar to human vision, or from space? The reason I ask is threefold. 1) Changes in the atmosphere might have caused tiny changes in "color" of the sun or the sky, 2) Solar flares, sunspots, halos (what are those?) would probably be almost impossible to see during the day with human vision without various optical tricks or instruments, and 3) illustrations of views from space have a lot more flexibility because they aren't always accurate – uhoh Apr 20 '17 at 7:13
• Can you just say explicitly the number of millions of years, don't make readers open up your chart in a new tab and try to read all those words and numbers please? Over the last 100 million years? Or the last 4 billion years? Most readers will not want to read about the Changhsingian/Wuchiapingian transition for example. – uhoh Apr 20 '17 at 7:15
• Maybe just keep the smaller one if you want, at the bottom. But in the main question just state in the first one or two sentences "4 billion years" or whatever number. First make it clear and simple just what specifically you are asking - very clear, and very early in the question. – uhoh Apr 20 '17 at 7:29

I'm doing some palaeobiology-landscape rendering; so I'm thinking if I want to add the sun in such pictures; should I draw it just like present day ?

Although the Sun was less luminous 4.5 billion years ago (about 70% of it's current luminosity, it is thought), and while this would affect it's color, making it perhaps a little more orange than yellow, the effect is small.

The Sun is still going to be a blazing near-white object in the sky of roughly the same size.

Although there was probably a color shift to a slightly more orange tint, the composition of the Earth's atmosphere was radically different (see for example this page on Paleoclimatology) and this would have had a much more significant effect on the appearance of the Sun (and the lighting of the landscape) than any minor change in the Sun's appearance.

There are some issues relating to the development of life and this change in the Sun's luminosity (like the Faint Young Sun Problem) but these won't make much difference to your rendering, I think, compared to the atmospheric and climate issues.

However the climate changes are not fully understood and it's rather speculative to try and make specific claims about what the overall effect would have been on the illumination levels and color of light reaching the surface in these periods.

• Thanks for this very-well-written, simple and nice answer. :) – Always Confused Apr 21 '17 at 19:44

You can divide this into two astronomical epochs, which are most easily understood in terms of the Hertzsprung-Russell diagram.

The first is the pre-main-sequence (PMS) phase, where the protosun contracts towards its main sequence, hydrogen burning, configuration. During this phase the (proto-)Sun declines in luminosity at roughly constant temperature for several million years, then heats up, with a slightly rising luminosity, before settling onto the main sequence with a slightly lower luminosity (see diagram below) after about 20 million years. The diagram gives you a rough idea of the "colour" that the protosun would have during this phase. The Sun is of course changing in brightness accordingly, but the radius of the Sun also decreases throughout this phase, so would cover a progressively smaller angle on the sky as seen from the Earth. $$R = \left(\frac{L}{4\pi \sigma T^4}\right)^{1/2}$$

A plot showing the paths (solid lines) of stars of different masses from birth (the Sun is still $\simeq 1M_{\odot}$ at birth) in luminosity and temperature, until they begin the H-burning main sequence. The dashed lines are "isochrones" at the indicated ages. The Sun "begins" its life (or at least emerges from its natal gas and dust less than a million years after birth) at the top of the $1M_{\odot}$ track.

The second phase is of course much longer, but the changes are far less dramatic. For the next 4.45 billion years the Sun just gets a little brighter and a little larger, but stays more-or-less at the same temperature. Over that time the Sun has got about 30% more luminous and 15% larger at a roughly constant rate.

If you need more detail than that, then you need to access a proper stellar evolutionary model. There are lots of those available. e.g. the Geneva models (the Schaller et al. 1992 set are appropriate for the Sun).

• What's the point in discussing the proto-sun? The OP says they're doing "palaeobiology-landscape rendering" of periods during Earth's history which would have been long after the proto-sun phase. As far as I read the question, only the last two paragraphs are relevant. – zephyr Apr 20 '17 at 13:35
• The chart in the question begins at -4.6 billion years. @zephyr I just went from that. The question also includes the "pre-Cambrian" period, a subset of which occurs whilst the Sun was a PMS star. I don't see the problem in providing a full answer. – ProfRob Apr 20 '17 at 15:20
• The ages are times since "birth" (a rapid event that takes less than a million years and leaves the protosun at the top of the 1 solar mass, $1M_{\odot}$ track). The plot only shows the first 20-30 million years of the Sun's life. The to-and-fro is no mistake and based on well understood physics. – ProfRob Apr 21 '17 at 7:35
• @AlwaysConfused -- The $10^4$ year, $10^5$ year, etc. curves represent the time from when a star is "born". Before this, a protostar collapses due to self gravitation. This collapse slows down markedly when a protostar becomes opaque, changing a protostar into a pre-main sequence star. – David Hammen Apr 21 '17 at 15:28
• The times are the times since the birth of a star. Tracks are shown for 7 stars with different masses. The appropriate one for the Sun is labelled as $1M_{\odot}$. The direction of the track is indeed in the direction of the arrows and towards increasing age. Ignore the thing labelled "birthline", it is an unnecessary complication here and is basically when the star becomes possible to observe. – ProfRob Apr 21 '17 at 16:25