Travel Through Time With The Summer Triangle

Aurora over Finland last night photographed by Ole Solomonsen

Always comes down to timing, doesn’t it?  Most of us never saw the auroras that arrived yesterday in the wake of last week’s solar eruption. They happened alright, but the show didn’t start until after sunrise and continued through daylight hours for North America. Siberians and Scandinavians were luckier. They had dark skies at the right time and got a real treat.

“After hours of waiting for the big aurora to show from the CME, and waiting for clouds to go away, I was about to give up. Then suddenly a spark on the horizon, which just grew, and grew and grew!”, wrote Ole Salomonsen who watched a beautiful aurora borealis unfold overhead from deep within a forest in northern Finland.

By the time darkness arrived in the U.S. Midwest, the northern lights had run out of steam. I looked – maybe you did too – but it was a no-show through midnight. Don’t give up! There’s still a chance tonight plus more goodies from the sun are on the way. NOAA space forecasters predict additional CME (coronal mass ejection) blasts both tomorrow and Thursday.

The brightest stars in the constellations Lyra (the Harp), Cygnus (the Swan) and Aquila (the Eagle) form a huge asterism in the sky called the Summer Triangle. Instead of distances, I’ve labeled the stars with the year the light you see tonight left each one. Created with Stellarium

One of late summer’s little astronomy joys is lying on your back and looking straight up at the Summer Triangle. You can do this with ease in early September when the three bright stars that form the triangle – Vega, Deneb and Altair – are due south as soon as the sky gets dark. Now tuck your hands back behind your head and join me for some time travel.

It takes just over 8 minutes for sunlight to travel the 150 million kilometers (93 million miles) to Earth. Credit: Wiki

Whenever we gaze at a celestial object we’re looking back in time. Even traveling at the unimaginable speed of 186,000 miles per second, light from distant objects takes time to reach our eyes. Moonlight needs 1 1/4 seconds old to get to Earth while sunlight takes just over 8 minutes. We might as well be watching a time-delayed TV program when we look up at the night sky.

Mars is 15 minutes away by light and the nearest star beyond the sun, Alpha Centauri, is 4.4 light years away. The light we see tonight departed its fiery surface in early 2008. No doubt about it – the stars are time machines of the imagination.

Cygnus the Swan and Lyra the Harp as seen from a mythological point of view. Credit: Urania’s Mirror

Let’s return to the Summer Triangle. Vega is almost directly overhead and a little off to the right (west) when darkness falls. It’s bright not only because it’s intrinsically luminous but also because it’s only 25 light years away. We see it as it shone in 1987 when a gallon of gas in the U.S. cost 89 cents, the home computer revolution was just getting underway and there were 5 billion humans on the planet. Today that number is over 7 billion.

Shifting your gaze to Deneb in the Northern Cross  – formally known as Cygnus the Swan – we peer much further back in time. Deneb is an extremely large and bright star, the reason it’s still a standout despite its whopping distance of 1,425 light years. That takes us to 587 A.D. when the Polynesian peoples first settled Hawaii and Tahiti. Europe was still dealing with deadly plagues in the 6th century while the Visigoth king in Spain converted to Christianity. It was a time of continuing conquests and wars following the end of the Roman Empire. So long ago, yet Deneb’s twinkle tweaks them back to life.

Altair sits near the head of Aquila (AK-will-uh) the Eagle. Credit: Urania’s Mirror

Altair lies at the base of the Summer Triangle and offers only a 17-year hop into the past. What were you doing in 1995 when there was no International Space Station to watch pass overhead at night?

Back then the brightest satellite was the Russian Mir space station, and we looked forward to its regular sweeps across the northern sky. On TV you’d see a lot of President Clinton and nearly as much of the O.J. Simpson trial.

Care to go back further back? The center star in the Cross, an easy naked-eye star called Gamma Cygni, is 1,800 light years from Earth, taking us back to 212 A.D., when the Chinese were inventing gunpowder and Emperor Elagabagus instituted sun worship in the Roman empire.

Since stars serve as such useful markers of our past, why not mix a little constellation study with history in the schools? Thanks to tireless efforts by astronomers and more recent measurements by the Hipparcos Space Astrometry Mission, we know the distances and look-back times of thousands of stars.  These tiny lights serve as reminders of  humanity’s long journey to the present.

4 Responses

  1. Bruce

    Thanks for the history lesson :). Never thought to think of a star as to when it’s light left vs. to see how long it would take to get there!

  2. Robert

    Love your websight. I live in Iowa and use your realtime aurora sightings to observe auroras. Even though I’m quite aways south of Duluth at least I know there are visible auroras out when you post, and judging how strong they are from your pictures and the KP index I know if they are visible from my area, really helps me out Thanks. My question- is a light year and an earth year the the same amount of time?

    1. astrobob

      Thanks very much for your kind words Robert. Light year vs. Earth year – two very different things. A light year is really a distance measurement. It’s how far light travels in one year. Since the speed of light is about 186,000 miles per second, if you multiply that by 365 days you get about 6 trillion miles. An Earth year is a measure of time and equals 365 1/4 days. Every 4th year, those 1/4 days add up to one full day – we add that onto that fourth year for 366 days or a leap year.

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