Bakersfield Night Sky – April 7, 2018
By Nick Strobel
Two Thursdays from now, on April 19, is the final evening Planetarium show of the spring season, “Incoming!” at the William M Thomas Planetarium. Narrated by George Takei, “Incoming!” explores the past, present, and future of our Solar System and the landmark discoveries scientists have made sending spacecraft to visit tiny worlds. Tickets can be purchased at the BC Ticket Office and online from Vallitix. The doors open up at 7 p.m. The first half of the show will be a tour of the April evening sky.
Three days before, on April 16, the next exoplanet-hunting spacecraft is set to launch from Cape Canaveral on Space X’s Falcon 9 rocket at 4:30 PM Pacific Time. Called “Transiting Exoplanet Survey Satellite” (TESS for short), the spacecraft will use the same technique that the spectacularly successful Kepler spacecraft used to find thousands of exoplanets (planets orbiting other stars): look for tiny dips in a star’s brightness as a planet moves in between us and the star. The bigger the exoplanet is, the more of the star’s light it will block and the bigger the dip in brightness will be. Where Kepler took a narrow but deep look, TESS is going to look in almost all directions but look at just the nearby 200,000 stars within about 300 light years of us.
Based on the statistics of stars with exoplanets orbiting them deduced from Kepler’s survey, we should find over 1500 exoplanets and several hundred should be rocky worlds the size of Earth on up to twice the diameter of Earth. We hope that at least 50 of these worlds will be close enough for their atmospheres to be studied by the James Webb Space Telescope, so TESS is sort of like a “finder scope” for the Webb. See https://tess.gsfc.nasa.gov/index.html for more about TESS.
Speaking of the James Webb Space Telescope, this successor to the Hubble Space Telescope is probably going to have its launch delayed to 2020 because of some problems that cropped up during testing of the components integrated together as a single spacecraft. Webb will be placed at the L2 Lagrange point, about 930,000 miles further out from the sun than Earth, so it will be out of reach for us to service it like we’ve been able to do with Hubble. That means everything on Webb must work perfectly the first time.
When deployed, Webb will have a mirror that is 6.5 meters across with a collecting area 6.25 times more than Hubble’s 2.4-meter mirror. It will be shielded from the sun’s and Earth’s heat by a five-layer sunshield about the size of a tennis court. Each layer of the sunshield is an ultra-thin membrane of Kapton just a hair-width thick coated with aluminum. All of it has to fit within a rocket payload, so the engineers have devised a clever origami-like folding sequence to get it to fit. The mirror itself is made of 18 hexagonal pieces of beryllium coated with a layer of gold just 100 nanometers thick mounted on three pieces that will fold up like the leaves of a drop-leaf table. Each hexagonal piece has to be aligned to 1/10,000th the thickness of a human hair.
Besides the rocket firings, I counted twenty sets of unfolding sequences that all have to work perfectly before Webb can even begin its science observations. I was in a state of speechless disbelief when I first saw the video of the deployment sequence. How many things could go wrong? How many of these things had been done before? Answers to the two questions: “too many” and “none”. The “From Dream to Discovery” planetarium show presented in mid-March showed some of the deployment sequence but I don’t think anyone can grasp the complexity of the deployment with just one viewing.
Webb’s primary science goals are: search for the first luminous objects formed after the Big Bang, determine how galaxies evolved from their formation billions of years ago to now, observe the formation of stars from the first stages to the formation of planets, and measure the physical and chemical properties of planetary systems and investigate the potential for life in those systems. These are the things we know we’ll do with Webb but like with Hubble, there will be a whole lot more done with Webb than we originally thought.
In our evening sky we’re now able to clearly see Venus low in the west after the twilight glow is gone. It will continue climbing higher away from the sun throughout the spring. Slightly dimmer than Venus but still brighter than any star in the night sky, Jupiter will rise about three hours after sunset. By the end of the third week of the month, we’ll be able to see Jupiter and Venus at the same time—just in time for the first KAS public star party at River Walk Park. The moon is at third (last) quarter tonight to the left of Mars and Saturn. Saturn and Mars are now moving apart from their conjunction in Sagittarius on April 2 but they are still close enough to appear in the same field of view of your binoculars. They’ll be high enough in the east to see by 2:30 a.m. The star chart below shows the view at 4 a.m.