The Biggest Star In The Sky And How To See It

Canis Major hosts the brightest star in the sky, Sirius, as well as our featured star VY. You'll find Sirius twinkling brightly about halfway up in the southern sky around 10 o'clock.

Astronomy is full of superlatives. Farthest, closest, hottest, densest, biggest, smallest. It’s fun to prowl around the sky in search of these extremes.

Two nights ago, I found myself star-hopping across Canis Major the Greater Dog in search of this or that gas cloud and spotted the star VY Canis Majoris on my atlas. The use of the lettered name “VY” tells us first off that this is a variable star whose light is not constant like the sun’s.

A quick check on the American Association of Variable Star Observers (AAVSO) website shows that VY varies between magnitudes 7.4 at brightest to 9.6. For the past few months it’s been around 8.0, bright enough to see in ordinary binoculars.

But its variability is not exactly the reason I wanted to acquaint you with this star. VY  is special for an entirely different reason – it’s the largest star known! Astronomers estimate its diameter at some 2,000 times the size of the sun. And since the sun is no slouch at 864,000 miles across, VY is truly a monster.

Illustration showing the size of the sun compared to VY Canis Majoris

Put in place of the sun at the center of the solar system, it would puff out beyond the orbit of Saturn. If the sun were reduced to the size of one of those big rubber balls people use as chairs these days, VY would be a much bigger ball 1.4 miles across. Yet another way to think of its vast girth is to compare how long it would take jet airliner traveling at 550 mph to fly across Earth, sun and VY:

* 14.5 hours non-stop to fly across Earth’s diameter of 8,000 miles
* 65.5 days to cross the sun
* 394 years to complete the 1.9 billion mile flight across VY

Thinking about that makes me want to stand up right now and stretch my legs.

VY is about 5,000 light years from Earth and classified as a red hypergiant star with a temperature of some 5000 degrees F. Surrounding the star is a small nebula of dust and gases VY has expelled in fits and starts during its evolution from a white supergiant star to its present state. Really big stars like VY eventually run of off nuclear fuel in their cores, collapse under the pull of gravity and then explode as supernovas. VY is so enormous that scientists predict it will one day become a powerful hypernova – ah, yet another superlative! – and might even collapse to form a black hole.

Use this detailed map, which shows stars to about 8th magnitude, to star-hop to VY and two other sky delights. North is up. Click map to go to the AAVSO site where you can print a more detailed map suitable for estimating VY's changing brightness. Maps created with Stellarium

You have plenty of time to see this magnificent star before that happens. First, shoot a line through the belt of Orion towards the east until you come to Sirius. An outstretched fist below Sirius, find a triangle of three easy-to-see stars, then use the detailed map (above) to star-hop your way to VY just as I did. For reference, the “triangle” fits nicely in a the field of view of typical binoculars.

NGC 2362 is one of the finest overlooked clusters in the sky. Credit: NASA

Those with telescopes are in for a treat. If the air is steady and you study VY closely at medium and higher magnifications, you’ll see a very small red-colored nebula around the star.This is material that’s been expelled during the star’s outbursts.

I’ve also included two other “must-sees” on the map — the beautiful, colorful double star h3945 which any scope can split into two and the stunning little cluster surrounding Tau called NGC 2362. See them all and you’ll have a most satisfying night.

21 Responses

  1. MBZ

    These little maps you make for us are just the greatest things ever. I spent a very enjoyable couple of hours last night hanging out in your “Milky Way Mansion”. The only thing missing was Jeeves with the Armagnac. Thanks so much for creating them.

  2. bobbi

    Hi Bob, i see that there was another solar storm on the 27 can you please tell me the difference between this one and the last one. Is this more powerful then the last?

    1. astrobob

      This one was strong – an X-class flare – but it was directed off the edge of the sun, not so much toward Earth. A smaller storm is predicted compared to the more direct hit from earlier this week.

  3. Lawrence Lathe

    I look about 22 degrees east of south . I see a star or ? flashing bright red and blue, this can be seen with the eye and much clearer with binoculars. What is this?

    1. astrobob

      Hi Lawrence,
      That’s the star Sirius. The twinkling or flashing is caused by air currents in the atmosphere.

  4. Angela Harper

    Sirius is also known as Sothis, i.e. the Goddess Aust {Isis}. The ancient Egyptians also called her the Dog Star. I was reading a chapter from The Egyptian Book Of The Dead, Which is also known as The Ancient Egyptian Book Of Life, Chapter LXV 2, the last sentance reads; The legs of Sothis are stablished, and I am born in their state of rest.”
    It would take far to much time and space to answer this, but the ‘legs of the Goddess Aust’, are the two moons that Sothis has. Funny thing, we didn’t know Sothis even had moons until 1995, how did the ancient Egyptians know this over six thousand years ago? Also a tribe called the Dogone in Africa knew about these moons thousands of years ago, and without a high powered scope, the only way they can be seen? I hope my spelling is correct, i have a hard time with it.

    1. astrobob

      Hi Angela,
      The Dog Star or Sirius has no moons or planets we’re aware of. It does have a small white dwarf companion star named Sirius B that was discovered in the 19th century. As you pointed out, it’s only visible in a good telescope at high magnification. There is no way the ancient Egyptians or anyone else without a telescope could have known of its existence. While the Dogon may have thought Sirius had a companion star, it couldn’t have been the current one, since it would have been as invisible to their unaided eyes as it is to ours today. My hunch is that it’s part of a myth.

  5. Glenn

    Hi Bob…

    If we were able to travel away for our Sun, how far out would we have to travel before our Sun was just a very dim speck in the sky?

    1. astrobob

      If you flew to the nearest star beyond the sun, Alpha Centauri, the sun would be an ordinary though bright first magnitude star in Cassiopeia. While I don’t know exactly, I would estimate the sun would be a dim speck at around 30 light years away.

  6. justus anying

    hi bob thanks for ur grandy once told me of a star that is seen after 75 yrs i believe its de star u say needs apowerful machine he said its bright & has a long tall like thanks

    1. astrobob

      It’s only because of its great distance from Earth. Same reason we can’t see some galaxies that are bigger than the Milky Way. Just too far away.

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