Andy Keen, who lives in Northern Lapland in Finland, had a great view of the northern lights last night. "The colours were fabulous - green, red, pink, turquoise, neon blue - the full works," he said. Details: 14mm lens at f/2.8, ISO 800 and 4-second exposure. Click image to see more photos and a video on Keen's website.
Bright auroras have dressed up the Arctic sky the past two nights after the sun’s wind of charged particles – electrons and protons – pried an opening in Earth’s magnetic field and spiraled down into the upper atmosphere. There’s still a possibility for aurora tonight primarily for those living in the far north. Take a look if clear skies are in your forecast. We’ve had clouds in my town and a now a blizzard on its way, so my eyes will be blinkered for a while.
The moon will be near the Seven Sisters star cluster tonight (Feb. 28) and the Hyades cluster tomorrow night. Created with Stellarium
Tonight the quarter moon is tucked under everyone’s favorite naked eye star cluster called the Pleiades (PLEE-uh-deez) or Seven Sisters. The cluster is shaped like a tiny dipper, and when the moon’s not quite so close to it, most of us see six or seven stars with ease. Binoculars show dozens more. The Pleiades, located about 400 light years from Earth, is a relatively young group of stars compared to our sun; their birth from a massive cloud of dust and gas happened during the age of the dinosaurs a mere 100 million years ago. It’s also the brightest star cluster in the sky.
The Hyades form a distinctive V-shape that represents the face of Taurus the Bull. The bright star at left, called Aldebaran, is a foreground star and not a member of the cluster. It's often referred to as the bull's eye. Photo: Bob King
One outstretched fist to the left or east of the Seven Sisters is a larger, looser star cluster called the Hyades (HY-uh-deez). It’s the closest star cluster to our solar system at a distance of 151 light years. That’s one of the reasons it appears larger and more spread out than the neighboring Pleiades. The Hyades occupy a volume of space some 30 light years across and are moving through space together like a school of fish.
Despite its closeness, the Hyades are fainter than the Pleiades because its stars are more than six times older with ages around 625 million years.
Clusters are born with stars of all different masses. Mass or the amount of stuff a star has determines its temperature, color and how fast it devours the nuclear fuel in its core. The biggest, brightest ones burn up their fuel fastest, either ending their lives as supernovas or evolving into dim white dwarfs. Because of the Hyades rather advanced age, its brightest stars have either blown up or faded away, leaving the smaller, fainter but more frugal fuel users – basically stars with masses similar to or less than the sun – dominating the herd.
Astronomers uses the "eyes" of the Earth on a particular date and then again six months later to measure a nearby star’s parallax or shift against the more distant background stars. Illustration: Bob King
The Hyades are probably the most famous star cluster in the world of astronomy, even eclipsing the Pleiades in importance. Why? Because they were a key steppingstone into deep space as astronomers looked for ways to determine distances to remote stars.
Astronomers use parallax, the apparent shift of nearby stars against the distant background stars when seen from two widely-separated points of view, to measure the distance to the closer stars. You can see a parallax shift when you hold a finger at the end of your nose while opening and closing your right and left eyes in a blinking pattern. Your finger will appear to shift back and forth against the distant background. Measure the distance between your eyes and the angle your finger makes, and you can find the distance to your finger with simple trigonometry.
In this illustration, you can see how a star shifts against the background ones when photographed through a high powered, professional telescope on opposite sides of Earth’s orbit. Illustration: Bob King
To measure the distance to a star using parallax, astronomers need a super-wide set of eyes, because even the closest ones are so incredibly far away, they show only minute shifts.
That’s where Earth’s orbit comes in (see above). We measure the star’s position against the background stars on one side of our orbit and then again six months later when we’re on the other side. Since we know the baseline length – 180 million miles – and can measure the parallax shift, we can easily calculate the star’s distance. It works beautifully - at least out to about 300 light years. After that, the shifts are too small to measure directly.
That’s where the Hyades come in. The cluster contain lots of stars of many different types, and since it’s so close, we can use parallax to measure its distance. Next we find a cluster with similar stars but too far away to show a shift and measure the brightnesses of those stars. Since we’ve determined that its stars are the same types as those in the Hyades but say, 100 times fainter, we know they must be 10 times farther away or approximately 1,500 light years from Earth. Bingo! We’ve taken another step deeper into the cosmos.
(Just an FYI – The intensity of light falls off as the square of the distance. It’s known as the inverse square law. 100 times fainter = 10 times farther. 10,000 times fainter = 100 times farther.)
Using the Hyades stars this way, astronomers have hopscotched into the depths of the galaxy. A most clever way to “expand” our universe, don’t you think? To learn more about parallax, please click HERE, and don’t forget to send the Hyades a “thank you” this week.