RACHEL
Welcome to Idaho Skies for the second week of February. We’re your hosts, Rachel…
PAUL
…and Paul.
RACHEL
The moon is new just after midnight on the 10th.
PAUL
This is why the faint Zodiacal Light remains visible for the first half of February.
RACHEL
The Zodiacal Light is a faint band of sunlight rising from the west after it gets dark.
PAUL
The sunlight in this case is reflection from interplanetary dust orbiting the sun.
RACHEL
You need to go outside an hour or more after sunset to see it. Be sure to observe from a dark location. The Zodiacal Light appears like the first light of dawn, except that it forms a pillar rising out of the west.
PAUL
The Zodiacal Light is also known as the false dawn.
RACHEL
The dust making up the Zodiacal Light is tiny. On average, it would take 10 grains stacked end to end to span the width of a human hair
PAUL
Mercury is climbing higher in the western sky for the next week.
RACHEL
If you want to see Mercury, look for it near the thin crescent moon on the evening of the 11th.
PAUL
The moon is less than two days old and a little bit above Mercury.
RACHEL
Since the moon and Mercury won’t be very far from the sun, they will be close to the horizon when the sky finally gets dark.
PAUL
So use binoculars and scan the west-southwest sky at around 7:00 PM. By 7:30, the pair will have descended too close to the horizon for your binoculars to find them.
RACHEL
Astronomer Fritz Zwicky would be 115 years old on the 14th.
PAUL
Fritz was a Swiss astronomer at Cal Tech. He coined the term supernova for the massive stars that collapse and end their lives in titanic explosions.
RACHEL
He also determined that supernovas collapse to form neutron stars.
PAUL
However, we know him better for his discovery about galaxies and the motions of their stars.
RACHEL
After measuring how fast stars orbit their galaxies, Fritz calculated the required mass of the parent galaxy.
PAUL
This led to his discovery that the number of stars within galaxies is too small to hold galaxies together by their gravity.
RACHEL
He reasoned that we were observing galaxies in the process of breaking up, which is very unlikely given the number of observable galaxies.
PAUL
Or equally unlikely, galaxies actually contain four times more matter than the number of stars lead us to believe.
RACHEL
Virtually no one listened to Fritz when he first discovered this discrepancy between the apparent mass of galaxies and the rotation rates of the stars within them.
PAUL
Eventually however, astronomers and physicists accepted his second conclusion and named this unseen matter, dark matter.
RACHEL
Dark matter is currently a subject of intense research.
PAUL
Cosmology suggests that around 80% of the matter in the universe is invisible to us. That is, it does not emit light or shine in reflected light.
RACHEL
Apparently, dark matter’s sole interaction with the matter that we are familiar with is through gravity.
PAUL
Imagine that. The world of matter we are familiar with only accounts for 20 percent of the mass of the universe.
RACHEL
Even more strange, the amount of matter and dark matter in the universe is small compared to the amount of mysterious dark energy that is causing the velocity between galaxies to increase.
PAUL
That’s Idaho Skies for the second week of February. Next week, you can observe an attractive grouping of the moon, two star clusters, and a planet. There is also an astronomy club meeting and two planetarium shows.
RACHEL
Follow us on Twitter at Idaho Skies for this week’s event reminders and sky maps.
PAUL
Be sure to read our blog for additional information. It’s at idahoskies dot blogspot dot com.
For Idaho Skies this is Paul…
RACHEL
and Rachel.
Idaho Skies is a production of NearSys and Radio Boise 89.9 FM Caldwell/Boise and 93.5 FM downtown, K228EK Garden City.
PAUL
Dark skies and bright stars.
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