Relative size of the earth, sun, planets, solar system, stars, universe

VV Cephei is an eclipsing binary star system located in the Cepheus (the King) constellation.

VV Cephei AWhat the? First I write about rugby, and now astronomy? I’m not deliberately trying to antogonise my readership—strangely silent since my recent piece on oval-ball madness. Let me try and explain…

Binary star systems consist of two stars which orbit each other. Kind of like soul mates, or eternal foes. The significance of binary stars to astronomers is that the relative rotation of each star allows them to precisely calculate their respective masses, and as we all know, astronomers like nothing more than a bit of calculator action. I do know this actually—I have a university astronomy paper to my name. But more on that later…

Binary orbits aside, VV Cephei A and VV Cephei B, or Tweedledum and Tweedledee if you prefer, are interesting because of their size. The Cephei twins, more big and little brother, red and blue respectively, are kind of big; VV Cephei B no smurf coloured slouch at approximately ten times the diameter of the Sun; VV Cephei A in fact one of the largest stars known, possibly the largest. Not just giant, but supergiant.

How big is a supergiant—astronomically correct term as well as accidentally cool moniker? In terms of our Sun, the foremost of the Cephi twins is 1600–1900 times larger, and 275,000-575,000 times as luminous. Were it located in our solar system, it would extend past the orbit of Jupiter and nearly to Saturn, and burns a fair number of candles, blazing into the night at 3300-3650 K.

Pretty big right? Incomprehensible even? If like myself you have a distinct aversion to the dryness of facts and figures, and a simultaneous desire to grasp reality between your fore-fingers rather than with the blunt pincers of your mind, have a look at the following animation, courtesy of, which illustrates graphically the relative sizes of a sequence of planets and stars, from the Earth and our Sun through to the supergiant VV Cephei A.

It’s enough to make you say “Wow!”


  • savannah
    Posted at 10:30h, 16 September

    (wow, lost my comment)

    anyway, what i said, i think, was….great post. i always lern something new from you, sugar! seriously, i knew ZIP about rugby…astronomy..a bit, but you reminded me of the real joy from just looking…

  • Sharani
    Posted at 13:39h, 16 September

    This was all new to me – I especially liked the animated view of it. Your post has put me in a sky frame of mind. Tonight as I walked in my neighborhood it was already dark before I returned and the crescent moon startled me for some reason with its beauty when I glimpsed it in the sky. Have you ever blogged about the moon?
    p.s. if you’re keeping score, add another one to the list who knew ZIP about rugby.

  • Jaitra Gillespie
    Posted at 13:56h, 16 September

    Thanks for the comments Savannah and Sharani—glad you enjoyed reading what was really just a few words and excuse to show a pretty cool video clip.

    Sharani, I haven’t blogged about the moon, and am not exactly sure why that is.

    The only connection with the moon I can think of is Yukio Mishima, whose final Sea of Fertility tetralogy was named after an area of the moon, and deliberately intended to convey both the appearance of beauty, and underlying barrenness that is the physical moon’s surface.

  • Sumangali Morhall
    Posted at 18:28h, 16 September

    Woooah stop the ride I want to get off!

    No wait, let me back on, this is *very* cool.

    I tend to thumb my nose at scientists, thinking they spend too much time with their calculators to appreciate the heart in God’s creation, but unless I knew mentally how outrageously beyond splendid some of His creations are, I would not be able to gasp at His Glory in so many ways. Once again I take my hat off to them.

    Here I am deciding what sort of tea to buy in the supermarket, while He’s out in His infinite Playground making supergiants for fun. Thanks for the perspective, (not to mention the very kind link to my article).


  • alf
    Posted at 20:52h, 18 September

    Astronomy has never been my strong point, but that was an excellent film for showing the relative size of things. I guess the binary twins have to be at least 10000 times the distance of our sun from earth or we would all be blind by now!

    I thought of Astronomy Domine, a song that I once liked but not so much now. It’s by Pink Floyd. There is an interesting performance and interview on YouTube. Actually the interview is the best part. First an introduction by the interviewer and then it starts again at 5 minutes or so. It really is quite amusing:

  • Jaitra Gillespie
    Posted at 13:48h, 20 September

    Thanks for the comment Sumangali—currently leading in the “Comment of the Week™” sweepstake, to be adjudicated at the end of the week.

    One of the things I have always found so fascinating about the (physical) universe is its sheer immensity—I memorised the speed of light as a child, prone as I was to contemplating the ming-boggling vastness of the distance between stars, and the amount of time it takes light to travel between them (not to mention the theoretical time it would take us to travel to them).

    Light-years, the distance light travels in a calendar year, is a fascinating concept—can one even begin to get one’s head around the concept that some parts of our night sky are visible now as they were 14 billion years ago?—so long and far have their persistent rays traveled to our distant shores—almost as old as creation itself.

    Bearing this is mind, I suspect God, an eternal child with an infinite playground, has long moved on from making supergiants—although they were quite the rage 14+ billion years ago, and is now near infinitely amused by His newer creations, a fascinated observer as they choose their tea at the supermarket.

  • Jaitra Gillespie
    Posted at 14:04h, 20 September

    How the world has changed Alf—you would never see an interviewer like that today, which I’m not 100% convinced is a good thing. Is he stuffy or civilised, boring or polite, lifeless or considerate and honest? The positives aren’t necessarily negative…

    I am reminded of the fact that this sort of music once literally gave me nightmares. I hated rock music with a passion as a child, and even more so psychedelia—mine was a deep sense of unease and ominous foreboding at their dischordant, hazy strains, as though chaos and destruction were beckoning dimly over a not far enough away horizon, a shapeless formless dread that couldn’t quite be put into words

    On the other hand, Syd Barret is considered by many to be a genius, and I am always interested in sampling genius when I find it.

  • alf
    Posted at 02:21h, 21 September

    I thought the interview was terrifically amusing. Hans was both pertinent and impertinent. Do the rock stars of today have such grace? An age of dignity has passed my friend and the world is much poorer for it.

  • crmrz1
    Posted at 12:07h, 16 April

    That’s so cool thank you for teaching me more about vv cephei i’m only 9 years old but i really love studying astronomy

  • lBig lB
    Posted at 07:34h, 15 June

    Dude, we are nothing. we’re smaller than atoms to the whole universe.

  • J.T.
    Posted at 19:51h, 21 July

    My questions are – Is it possible that our solar system is a rotation within a rotation, stars included, and we actually rotate around the biggest star, hence, all of the stars that we see, seem to stay in the same place, as well as evolve? Is it possible that some of the stars that we see in the far distance are actually planets that have life forms on them, we just can’t see close enough to tell?

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