Bakersfield Night Sky - October 3, 2021
Bakersfield Night Sky — October 3, 2021
By Nick Strobel
There are five gravitational balance points (“Lagrangian points” for those playing Jeopardy) for the Earth-Sun system. A small satellite can orbit these points in a constant manner. The L1 point is directly between Earth and the sun at 1.5 million kilometers from Earth—much closer to Earth than the sun because of Earth's much weaker gravity. Some of our sun-observing science satellites (e.g., SOHO) have been situated there as well as the Deep Space Climate Observatory (DSCOVR) satellite. The L2 point is located 1.5 million kilometers directly behind Earth with respect to the sun. The L3 point is on the exact opposite point of Earth's orbit around the sun, so we cannot see anything there from Earth because the sun is always in the way.
The L4 and L5 points are gravitationally stable points in Earth's orbit that are 60 degrees ahead and 60 degrees behind Earth, respectively. A gravitationally stable point means that if a satellite starts to drift away from the L4 or L5 point for some reason, the gravity of Earth and the sun would nudge it back toward the L4/L5 point. Back in the 1970s Gerard O'Neill popularized the idea of building giant space stations at the L4 and L5 points in which many thousands of people would live in self-sustaining colonies independent of Earth. I devoured his book, “The High Frontier: Human Colonies in Space” when I was in junior high school (we didn't have “middle school” where I grew up). There are some small asteroids found orbiting the Earth's L4 and L5 points but Jupiter's L4 and L5 points have thousands of asteroids, called the Trojan asteroids.
On October 16, NASA will launch the Lucy spacecraft to be the first space mission to study the Trojan asteroids. These asteroids are thought to be the leftover remnants of the material that formed the outer planets. They may even hold clues to the origin of organic material on Earth. Lucy is going to take a complex path over 12 years to study 8 different asteroids—a main belt asteroid called “Donaldjohanson” in the asteroid belt between Mars and Jupiter in mid-April 2025, and then seven Trojans: four in the leading L4 group in August 2027 to November 2028, and three in the trailing L5 group in March 2033.
Lucy will visit examples of all three major types of Trojans: the dark-red P- and D-type Trojans have spectral light characteristics similar to the Kuiper Belt of comets beyond the orbit of Neptune and the black C-type that are like many of the main belt asteroids. Lucy will be powered by two large round solar panels each about 24 feet across that will generate up to 504 watts at its farthest distance from the sun. Lucy's orbit will allow it to continue visiting the Trojan asteroids for many thousands of years, though the funding to keep in contact with Earth will probably run out before then.
As I mentioned above, Earth's L2 point is directly behind the Earth and as such, spacecraft can keep the sun, Earth and moon behind the spacecraft for solar power while having a clear view of deep space. Spacecraft at L2 are close enough to have easy communication with the teams on Earth but are far enough away to not sense the infrared glow of the warm Earth. The recent Planck mission that mapped the Cosmic Microwave Background to the highest resolution ever, is located at L2 as is the currently-operating Gaia mission that is plotting the positions and velocities of over a billion stars in our home galaxy, the Milky Way.
At the end of October, NASA will launch another space observatory to the L2 point, the James Webb Space Telescope. With a mirror 6.5 meters across, Webb will be the largest observatory put into space. It will be the successor to, not a replacement of, the Hubble Space Telescope. Hubble observes primarily in ultraviolet and visible wavelengths, while Webb will observe in the longer wavelengths of infrared, so it can see the first stars that formed in the universe as well as peer into the dusty cocoons surrounding nearby forming stars and planets and take detailed spectra of the atmospheres of nearby exoplanets. Hubble has been able to do imaging and spectroscopy in the “near infrared”—wavelengths slightly longer than the visible band of colors we can see with our eyes—but Webb will observe in significantly longer infrared wavelengths. Since the resolution or clarity of a telescope decreases with increasing wavelengths, telescopes need to be correspondingly larger in diameter to achieve the same resolution. That is why radio telescopes are tens of meters across. Webb's mirror needs to be over twice the diameter of Hubble's mirror to get the same resolution in the infrared as Hubble has in the visible.
How do you get a telescope with a mirror far larger than can fit in any rocket to operate successfully at a point over three times farther than the moon? I'll talk about that in my next column.
If you're vaccinated, you have a MUCH smaller chance of getting so sick that you need to be hospitalized in Kern's already packed hospitals. Check out My Turn vaccination information page for the clinic closest to you and please continue wearing a mask when with large groups in enclosed spaces!
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Nick Strobel
Director of the William M Thomas Planetarium at Bakersfield College
Author of the award-winning website www.astronomynotes.com
