What Would The Sky Look Like If Arcturus, Sirius Or Alpha Centauri Were Our Sun?

If Arcturus were put in place of the Sun it might look something like this at sunset, which would last an unusually long time given the vast dimensions of the star, some 25 times larger than our Sun. Credit: Roscosmos

I was out walking the other night around 11 o’clock when I noticed a new bright star poking through the trees low in the northeastern sky. For a moment I couldn’t figure it out, and then it came to me. Arcturus.

Arcturus, an orange giant star some 21 million miles in diameter, compared to the sun, Jupiter and other familiar stars.

Arcturus is a traditional spring-early summer star as that’s when it’s highest in the sky. But winter’s the time it first appears in the east as the midnight hour approaches. Arcturus is an orange-giant star 25 times larger than the Sun 36 light years from Earth.

If you’ve ever wondered how it might look in our sky, Russia’s Federal Space Agency or Roscosmos, has created a series of fun and instructive simulations of several familiar stars,including Arcturus, in place of the Sun.

While the Sun takes about two minutes to set once it touches the horizon, Arcturus’ massive disk would extend some13° across and require 52 minutes. Watching an Arcturian sunset would be a major time commitment reserved for weekends only.

Here are several other new stellar perspectives. In all, except perhaps Alpha Centauri, the Earth would roasted in the stars’ blazing heat and radiation. Keep that in mind as you take in the sights.

White-hot Sirius would blaze in our daytime sky. 1.75 times the size of the Sun and 26 times as luminous, we’d all be fried if Sirius stood where the Sun is. Credit: Roscosmos
How about a familiar triple star? This is Alpha Centauri, comprised of two stars slightly more massive and luminous than the Sun located 4.47 light years away. The third star (to the left) is Proxima Centauri, a dim red dwarf and third member of the system. Credit: Roscosmos
Vega in the constellation Lyra is our sit-in sun in this simulation. The star, 25 light years from Earth, rotates so rapidly it’s oval shaped instead of spherical. Vega measures 2.7 times the Sun’s diameter along its equator and is 36 times brighter than the Sun. The sight would make you go blind quickly. Earth would also be roasted in the heat. Credit: Roscosmos
Polaris or the North Star is a yellow supergiant 2,500 more luminous than the Sun and 45 times its size. What an eyeful we Earthlings would have if Polaris were our sun. Credit: Roscosmos

Here’s the whole works and more in a video in Russian. Enjoy! Tomorrow the fun continues when we’ll take a look at substituting planets and moons for the Sun.

9 Responses

  1. Richard Keen

    That’s got me humming “Moscow Night”, or a version more like “Moscow Days”.
    Not to be a nit-picker, though I am, but these are all views of the stars from 1 astronomical unit, right? Since the double stars of alpha Centauri are 23 AU apart, the Earth would be orbiting one or the other of the pair, so the “other” of the pair would be 23 times farther away, or 6 to 8 magnitudes fainter. It would also most likely be somewhere else in the sky.
    Details, details….
    Otherwise, neat pictures!

    1. astrobob

      Hi Richard,
      I agree. Some liberties were taken with Alpha Centauri – idealized a bit but perhaps just for the sake of including all three in the same view. The others seem good, and I was especially impressed that they got the shape of Vega correct.

  2. Edward M. Boll

    If Arcturus were our star would it ever get real dark at night? Speaking of bright nights, Lovejoy is getting hard to see in moonlight with binoculars. I thought about going out tonight, but we have clouds with snow moving in.

    1. astrobob

      Edward,
      Excellent question! If we apply the same -18 degree altitude criterium as the end of astronomical twilight, then the sky from mid-northern latitudes would never get dark from about May 15 to August 1. However, Arcturus has an absolute magnitude of -0.3 compared to the Sun’s +4.8. That makes it 100x brighter, so it would eat into the darkness and with twilight nights no matter the season.

    1. astrobob

      Edward,
      Steady was the last I heard but there’s precious little for visual observations with the bright moon. Usually these fade. Photographs show no additional brightening.

  3. Thomas V Koehler

    The displays of the various planets in our sky, were they to replace our moon raises the question of what the Earth would be like. The tidal effects of the moon helped create our planet as we know it. I am assuming the tidal effects of these larger masses would have dramatic effects on Terra. Wicked crazy tides and heaving of our planets crust are possibilities that come to my mind for the larger planets. We might periish from the effects on our climate. ??

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