Tuesday, January 17, 2017

January's Star is Rigel


This month’s star is Rigel, the blue-white star marking Orion’s left foot. Rigel is called Beta Orionis by astronomers. To appear as the 7th brightest star in the sky at a distance of 863 light years, Rigel has to be a very large and massive star. Therefore, it’s not surprising to learn that Rigel is 120,000 times brighter, 25 times more massive, and 96 times larger than the sun. If it replaced our sun, the surface of Rigel would engulf poor little Mercury. It would appear some 45 degrees across in our sky and roast Earth’s surface to death.

Like people, stars this massive don’t live long. It appears Rigel is only 8 million years old and it’s already used up its original supply of hydrogen. The star is now consuming its supply of helium ash. In star years, Rigel will not last much longer. And when it does go, it will explode as a supernova and send the heavy metals it has generated over its short life across this region of the galaxy. As a result, future stars will form with more elements like carbon, oxygen, iron, and gold.  

The star’s name comes from the Arabic word for foot (in Arabic, the star is called the foot of the great one). The oldest reference to its current name goes back to the 13th century.

Rigel can be seen in the low southeast before the sky gets completely dark in January.

Transcript for January 20th to 22nd

RACHEL
Welcome to Idaho Skies for January 20th, 21st, and 22nd. We’re your hosts, Rachel...

PAUL
...and Paul.

RACHEL
Stargazers should start looking for earthshine on the morning of the 22nd.

PAUL
Earthshine is also called the moon’s Ashen Glow.

RACHEL
Stargazers will notice the dark portion of the moon is not actually black.

PAUL
Instead, it’s faintly illuminated.

RACHEL
In binoculars, that illumination is bright enough to show some lunar details.

PAUL
Details like the lunar seas or maria.

RACHEL
We know that the illumination comes from sunlight reflecting off of Earth.

PAUL
It was Leonardo da Vinci in the 1500s that explained the moon’s ashen glow as the result of sunlight reflecting off of Earth.

RACHEL
Did you know that by monitoring earthshine, scientists can determine the percentage of Earth’s cloud cover?

PAUL
That’s because earthshine is brighter when there are more clouds.

RACHEL
Long term variations in cloud cover can be determined this way since there are records of the brightness of earthshine.

PAUL
Earthshine is one example of planetshine.

RACHEL
Planetshine is the general term for the illumination of satellites by the reflection of sunlight off of any planet.

PAUL
And it’s been observed on the moons of Saturn by the Cassini spacecraft.

RACHEL
Planetshine has allowed the spacecraft to map the surfaces of moons when they were not properly illuminated by sunlight.

PAUL
By the way, some of the dark hemispheres of Saturn’s moons were observed using sunlight reflecting off the planets rings.

RACHEL
Let me guess, this is called ringshine.

PAUL
Yep.

RACHEL
That’s Idaho Skies for the 20th, 21st, and 22nd of January.

PAUL
Be sure to read our blog for additional information. It’s at idahoskies.blogspot.com.

For Idaho Skies this is Paul...

RACHEL
...and Rachel.

RACHEL
Dark skies and bright stars.

Transcript for January 18th and 19th

PAUL
Welcome to Idaho Skies for January 18th and 19th. We’re your hosts, Paul...

RACHEL
...and Rachel.

PAUL
There’s an astronomical trio on the morning of the 19th.

RACHEL
To see this sight, go outside at about 3:00 AM and look for the moon in the low southeast.

PAUL
The moon is the first of the trio.

RACHEL
The other two are the planet Jupiter and the star Spica.

PAUL
Jupiter is the bright creamy white star located to the right of the moon.

RACHEL
Spica is a whiter spark of light and it’s located to the moon’s lower right.

PAUL
The moon is in the last quarter phase.

RACHEL
That means stargazers with a pair of binoculars can enjoy the trio even more.

PAUL
When they point binoculars at the moon, it will show lots of craters, especially strewn across its southern hemisphere.

RACHEL
Jupiter on the other hand will show no surface detail.

PAUL
However, its four largest satellites will appear in a line on the right side of the planet.

RACHEL
It might be tough to see Ganymede, because of how close it appears to the glare of Jupiter.

PAUL
The other three will definitely be easier to see.

RACHEL
They are, going from closest to Jupiter to farthest, Ganymede...

PAUL
...volcanic Io...

RACHEL
...icy Europa...

PAUL
...and finally Callisto.

RACHEL
These four satellites are close to the size of our moon and yet, binoculars can show them from 480 million miles away.

PAUL
Imagine what Earth and the moon would look like from Jupiter?

RACHEL
That’s Idaho Skies for the 18th and 19th of January.

PAUL
Be sure to follow us on Twitter at Idaho Skies for this week’s event reminders and sky maps.

For Idaho Skies this is Paul...

RACHEL
...and Rachel.

PAUL
Dark skies and bright stars.

Transcript for January 16th and 17th

RACHEL
Welcome to Idaho Skies for January 16th and 17th. We’re your hosts, Rachel...

PAUL
...and Paul.

RACHEL
In order for American astronauts to go to the moon, the United States had to learn how to dock two spacecraft.

PAUL
Surprisingly though, this feat was first accomplished by the Soviet Union on January 16th, 1969.

RACHEL
Or six months before the first moon landing.

PAUL
This was the third docking attempt by the Soviet Union.

RACHEL
The previous missions all failed to dock and one cosmonaut’s life was lost.

PAUL
On January 16th, Russian cosmonaut Vladimir Shatalov was launched into Earth orbit onboard the spacecraft Soyuz 4.

RACHEL
Cosmonauts Aleksei and Yevgeny rode Soyuz 5 into orbit and rendezvoused with Soyuz 4.

PAUL
The cosmonauts spent an hour transferring from Soyuz 5 to Soyuz 4.

RACHEL
Why did it take so long?

PAUL
Because there was no tunnel between the docked Soyuz 4 and Soyuz 5 spacecraft.

RACHEL
In other words, the cosmonauts spent an hour performing a spacewalk to transfer from Soyuz 5 to Soyuz 4.

PAUL
Two months later, a Saturn V would carry Apollo 9 and its lunar lander into Earth orbit.

RACHEL
American astronauts McDivitt and Schweikart tested the lunar lander in Earth orbit.

PAUL
And then docked with astronaut Scott in the Apollo 9 spacecraft.

RACHEL
They were able to transfer back again to Apollo 9, but used a tunnel connecting the two spacecraft.

PAUL
In January 1969, the Soviets were still planning to send cosmonauts to the moon.

RACHEL
But they would have to perform an EVA to transfer from the lunar lander back to their spacecraft.

PAUL
That’s Idaho Skies for the 16th and 17th of January.

RACHEL
Be sure to read our blog for additional information. It’s at idahoskies.blogspot.com

For Idaho Skies this is Rachel...

PAUL
...and Paul.

RACHEL
Dark skies and bright stars.

Monday, December 19, 2016

Transcript for December 23rd to 25th

RACHEL
Welcome to Idaho Skies for December 23rd, 24th, and 25th. We’re your hosts, Rachel...

PAUL
...and Paul.

RACHEL
The moon, Jupiter, and Spica form an astronomical trio on the morning of the 23rd.

PAUL
Earthshine should be easier to see the morning of the 23rd than it was a day ago.

RACHEL
You’ll need to be outside some time between 4:30 AM and 7:00 AM.

PAUL
That’s between the time of moonrise and the break of dawn.

RACHEL
Zubenelgenubi is a double star that appears as a single star to most people.

PAUL
Stargazers with binoculars won’t be tricked however.

RACHEL
That’s because it takes only a little magnification to split the star into two companions.

PAUL
Stargazers can find this double star for themselves on the morning of the 24th.

RACHEL
It’s easier that morning because Zubenelgenubi is the star below the crescent moon at 6:00 AM.

PAUL
You’ll find that the moon and Zubenelgenubi so close enough together, that you can see both at the same time in binoculars.

RACHEL
But just barely.

PAUL
Did you get a telescope on Christmas Eve or very early Christmas morning?

RACHEL
Then put a low power eyepiece into the telescope and point it at the thin crescent moon at 6:00 AM on the 25th.

PAUL
By the way, a low power eyepiece is one with a large focal length.

RACHEL
So a 25 or 50 mm eyepiece would be ideal.

PAUL
Stargazers will see earthshine illuminating the dark portion of the moon.

RACHEL
And sunlit craters nearly edge-on.

PAUL
Their shadows will be cast long...

RACHEL
...but those shadows are pointing towards Earth so we see them strongly foreshortened.

PAUL
That’s Idaho Skies for the 23rd, 24th, and 25th of December.

RACHEL
Be sure to read our blog for additional information. It’s at idahoskies.blogspot.com.

For Idaho Skies this is Rachel...

PAUL
...and Paul.

RACHEL
Dark skies and bright stars.

Transcript for December 21st and 22nd

PAUL
Welcome to Idaho Skies for December 21st and 22nd. We’re your hosts, Paul...

RACHEL
...and Rachel.

PAUL
Winter begins on the morning of the 21st.

RACHEL
So give a warm welcome to the winter solstice.

PAUL
Wait, solstice?

RACHEL
The word solstice means sun standing still.

PAUL
Standing still?

RACHEL
Sure. It refers to the fact that the sun’s point of rising on the horizon doesn’t appear to shift for several days.

PAUL
Oh I see. Normally, stargazers would notice the sun rises in a more northerly point during the winter and spring.

RACHEL
And rising more southerly point during the summer and fall.

PAUL
So on the first day of winter, that motion temporarily halts.

RACHEL
Hence the name, solstice.

PAUL
Early risers will find three astronomical treats in the low southeast on the morning of the 22nd.

RACHEL
First is a very bright Jupiter below the second treat, the crescent moon.

PAUL
The third treat is a slightly fainter star below Jupiter, the star Spica.

RACHEL
Spica is the brightest star of Virgo the Maiden.

PAUL
Finally, earthshine or the faint illumination on the dark portion of the moon may also be visible that morning.

RACHEL
A pair of binoculars will come in handy for seeing earthshine.

PAUL
Which is actually sunlight, but reflected from Earth first.

RACHEL
That’s Idaho Skies for the 21st and 22nd of December.

PAUL
Be sure to follow us on Twitter at Idaho Skies for this week’s event reminders and sky maps.

For Idaho Skies this is Paul...

RACHEL
...and Rachel.

PAUL
Dark skies and bright stars.

Transcript for December 19th and 20th

RACHEL
Welcome to Idaho Skies for December 19th and 20th. We’re your hosts, Rachel...

PAUL
...and Paul.

RACHEL
Stargazers going outside after midnight on the 19th will find Leo the Lion sitting on top of the moon.

PAUL
Leo is one of the original 48 constellations recorded by the ancient astronomer Ptolemy.

RACHEL
Ptolemy was a Greek astronomer living in Alexandria, Egypt in the 2nd century AD.

PAUL
Leo was an ancient constellation for Ptolemy because the Mesopotamians recognized it as a lion 4,000 years earlier.

RACHEL
Residing inside the boundary of Leo is a star that astronomer Max Wolf listed as the 359th star in his catalog.

PAUL
He was developing a catalog of stars that were moving quickly across the sky.

RACHEL
This movement is called proper motion and a good way to detect stars that are close to the solar system.

PAUL
Today astronomers call the star Wolf 359.

RACHEL
At a distance of 8 light years, Wolf 359 is the fifth closest star to the solar system.

PAUL
The star appears in several science fiction stories, including Star Trek the Next Generation.

RACHEL
The star is so faint that a large amateur telescope is needed to see it.

PAUL
Why is it so faint if it’s so close to the solar system?

RACHEL
That’s because it’s a low mass red dwarf star.

PAUL
Astronomers discovered early last century that the lower the mass, the fainter the star.

RACHEL
In the case of Wolf 359, it only has 9% of the mass of the sun.

PAUL
That low mass comes with a benefit however.

RACHEL
Astronomers calculate that the star will continue to shine until a ripe old age of 8 trillion years.

PAUL
Which is almost 800 times longer than the sun.

RACHEL
So when the sun is long gone, Wolf 359 won’t even be 1% older.

PAUL
That’s Idaho Skies for the 19th and 20th of December.

RACHEL
Be sure to read our blog for additional information. It’s at idahoskies.blogspot.com

For Idaho Skies this is Rachel...

PAUL
...and Paul.

RACHEL
Dark skies and bright stars.