In my last entry I talked about some of the strange and unusual effects that a visitor to my hypothetical planet ‘Esurio’ might witness. We’ve already established there is no day or night, nor seasons in the traditional sense. Part of the planet would be in perpetual frozen darkness and the other in unceasing sunlight.

Red dwarf stars, like Lalande 21185 in this particular case, are very different from our Sun. We’re so used to our familiar yellow star that it takes quite an effort of imagination to envisage something different. The view from Esurio would be unfamiliar to us.
Firstly, Red Dwarfs are much smaller than yellow ‘G-Type’ stars like our Sun. Lalande is estimated to be only 40% of the diameter. They’re also much less bright, of the order of a mere 1% or thereabouts. Planets needs to be much much closer to stay warm.
How close? Astonishingly close actually.
In our solar system, the planet Mercury (closest to the Sun) orbits at about 36 million miles average distance. At this range the surface temperature is over 300 celsius. Earth, by comparison, is 93 million miles away. To stay warm enough around a Red Dwarf, my planet ‘Esurio’ would have to be a mere 1.3 million miles away.
At this range, as we’ve already discussed, Esurio would be tidally locked with Lalande motionless in the sky. But the view would be nothing like it is on Earth, because Lalande would be much bigger in the sky than our Sun is.
How much bigger? What would that look like?
Fortunately, a bit of simple mathematics provides a rough result. We can use trigonometry to find the answer for us. Don’t be scared, I’ll do the maths for you!
Let’s work it out for the Earth and Sun first, by comparison. We know the Sun is about 864,400 miles across and is 93,000,000 miles away.
The formula is:
tan (x) = 864,000 / 93,000,000
x = 0.53 degrees
In other words, if we imagine the whole of the sky as a 360 degree sphere, the Sun (and our Moon for that matter) appears to be around half a degree across in the sky. Not all that much really.
What about on Esurio?
Lalande is smaller than the Sun at a guesstimated 345,760 miles in diameter, but we’re much closer, at around 1,395,000 miles. Let’s do the maths again.
tan (x) = 345,760 / 1,395,000
x = 13.92 degrees
So in the skies of Esurio, the star Lalande would appear about 28 times wider than the Sun does when viewed from Earth. About 1/6 of the width of the sky covered by the star – a huge sphere. Quite a view!
Wouldn’t that be blinding? Well, no apparently not. Red Dwarfs are incredibly dim when compared to our familiar Sun. The illumination level would be very similar to the interior of a room lit by old fashioned incandescent bulbs.
There is a tendency for us to think everything would look ‘red’ too, but this would not be the case. Our eyes would quickly adjust to the frequency of light and compensate, much as they do when we first go into illuminated rooms after being out in bright sunlight. It might not be the best choice of holiday for those amongst us who suffer from SAD (Seasonal Affective Disorder) though!
At this distance, the features on the surface of the star would be plainly visible, particularly sunspots and faculae. How might the appearance and disappearance of these features be interpreted? What a good plot device…
And the sky itself? Surprisingly mundane. It would probably be blue-ish, much like the sky on Earth. The colour of the sky is caused by short wavelength blue light being scattered by the molecules that compose the atmosphere. Assuming the atmosphere is similar to Earth (and it would have to be for people to live there) we get the same result.
Another side effect of Red Dwarfs is that they don’t emit anywhere near the amount of visible light that we’re used to here on Earth. Other than for illumination this doesn’t really matter to animals and humans as our eyes are sensitive enough to cope, but plants are a different matter. Green leaves wouldn’t work so well. To work effectively it seems likely that leaves on Esurio would be black, evolving to pick up the lower energy photons from Lalande.
Plants would thus be very different to those on Earth, which means the animals would be different too…
The Shadeward Saga by Drew Wagar is an upcoming series of Sci-Fi ebooks, set on the tidally locked world of Esurio in the Lalande 21185 star system.