Spica

The night sky is filled with stars, every child knows that. They are not always visible due to weather or light pollution, and you cannot see them by day...but they are there. They are our constant companions.

I remember when I learned that stars were other suns, very far away. That fact still amazes me.

There is one star in particular that has become my favorite. I often have trouble falling asleep at night and I sleep near the window so I look up at the starry sky and think about the stars. The brightest star I can see is much brighter, from Earth anyhow, than the others in my window. This star is a kind of nighttime friend now, it stays up when I can't sleep and I can always count on it.

It's called Spica.

Spica is a very cool star to know. In fact it's actually not one star - it's two! Yep...Spica A/B is a close-binary system, which means that when you look at Spica you are really looking at two suns orbiting each other at a very close distance...so close that optical telescopes cannot resolve the two separate stars - they appear as one. The only way we know they are two is by taking careful measurements of Doppler Shift in their spectra - the slight shift in the area indicates that there are two stars moving in different directions.

Spica has a long history with human interaction, and has been known by many other names throughout the centuries: Alpha Virginis (α Virginis), Azimech, Alaraph, Dana, 67 Virginis, and of course the various star catalog designations: HR 5056, BD -10°3672, HD 116658, GCTP 18144, FK5 498, CCDM 13252-1109, SAO 157923, HIP 65474.

- Spica is thought to be the star upon which Hipparchus based his discovery of the precession of the equinoxes.

- There is a temple in Thebes, built in 3,200 BC, that was oriented to line up with Spica. (Due to the age of the temple and the shifting movement of the stars, it no longer lines up, but we know it did 5,200 years ago).

- Copernicus himself made numerous observations of Spica.

Yeah, we go way back with this star.

Spica has been studied extensively by us humans, for many years. We have reams of data relating to every feature and classification we can think of on this star. Here are some astronomical specs for my favorite friend-star.

Spica is:

- The brightest (Alpha) star in the constellation Virgo, and the 15th brightest star in the night sky.

- Spectral Type B1 III-IV/B2 V. This means the star is blue-white, very hot and very bright (which, duh, we already know by looking out the window), B is the second hottest classification. Only about 1% of all stars are in this class. Our sun is a much cooler yellow-white star with Spectral Type G.

- A "double-lined spectroscopic binary" with a primary radius of 7.4 times our sun and a mass of 10.25 times our sun.

- Positioned 260 light years from Earth, which means the light I see when I gaze upon it left Spica in the year 1750!!

- The primary (brightest) star in Spica has a luminosity of 12,100 times that of our sun.

- Is classified as a Beta Cephei type variable star - it pulsates and contracts in a period of about 1/5 of an Earth day. It is also rotating very rapidly. The pulsation is caused by the close proximity of the secondary (dimmer) star...these two are so close together their gravities distort each other, giving them yet another classification: "rotating ellipsoidal variable non-eclipsing" star.

- Spica is a young star. Over time, the system may stabilize and the two components could get themselves into a nice circular orbit with each other. But for now, they fight it out.

Whew! That's complicated stuff and we haven't even scratched the surface of what humans know about this star.

But for me, on those sleepless nights, I don't think much about Spectral Types or classifications. I just think about how friendly they are.

At least, I know my Spica is.

P.S. If you're ever in the stellar neighborhood and find you cannot sleep, stop by and say hello to my friend. Just follow the curve of the Big Dipper's handle right through Arcturus and then drop on down!