Latest / Star Trails: From Backyard Astronomy to Cosmic Wonder / A Dark Sky for Us, and a New Moon for Uranus

Transcript

A Dark Sky for Us, and a New Moon for Uranus · Star Trails: From Backyard Astronomy to Cosmic Wonder

• 0:07
  Howdy Star Gazers and welcome to Star Trails.
• 0:10
  I'm Drew and I'll be your guide to the night
• 0:13
  sky for the week of Sunday, August the 24th to
• 0:16
  the 30th. This is a week that begins in darkness
• 0:20
  and ends with a silver lantern in the sky, thanks
• 0:24
  to a waxing moon. We'll take a look at what else
• 0:27
  is up this week and in the second half of the
• 0:30
  show, We journey out to Uranus where a tiny new
• 0:33
  moon has just been discovered. More importantly,
• 0:37
  we wonder, what would it be like to walk around
• 0:40
  this tiny moon? Whether you're tuning in from
• 0:43
  the backyard, the balcony, or just your imagination,
• 0:47
  I'm glad you're here. So find a cozy spot, let
• 0:50
  your eyes adjust, and let's see what the sky
• 0:53
  holds for us this week. The new moon slipped
• 0:57
  past us on August the 23rd, which means the first
• 1:01
  half of this week belongs to deep -sky hunters,
• 1:05
  galaxies, clusters, and nebula without the lunar
• 1:08
  washout. But each evening, the waxing crescent
• 1:11
  grows larger, rising higher in the west until
• 1:14
  it becomes a bright beacon by Saturday night.
• 1:18
  Try for the razor -thin crescent earlier in the
• 1:21
  week low in the west 20 to 45 minutes after sunset.
• 1:25
  By the week's end, the crescent is high enough
• 1:28
  to sketch shadows along the terminator when viewed
• 1:30
  with binoculars. Saturn is the planetary star
• 1:34
  of the show this week. It lifts itself into the
• 1:37
  southeastern sky by mid -evening. Its rings tilted
• 1:41
  just enough to remind us why Galileo once called
• 1:44
  them ears. A small telescope will reveal Titan
• 1:48
  as a tiny golden companion. and with larger optics
• 1:52
  you'll spot multiple moons strung like faint
• 1:55
  pearls nearby. Look east before dawn and you'll
• 1:59
  find a brighter spectacle, Venus blazing like
• 2:02
  a spotlight with Jupiter tagging along. They've
• 2:06
  been in conjunction recently, but even as they
• 2:08
  drift apart they still share binocular fields
• 2:11
  like two bright exclamation points in the morning
• 2:14
  twilight. In the evening, Mars is hanging low
• 2:18
  in the western twilight for about 45 -60 minutes
• 2:22
  after sunset. It's small and faint now, so we
• 2:25
  can treat it as a goodbye glance object this
• 2:29
  week. Uranus rises around midnight, high before
• 2:33
  dawn, in Taurus, drifting beneath the Pleiades
• 2:36
  this month, which makes it an easy star -hop
• 2:39
  target for 50 -70mm binoculars under dark skies.
• 2:45
  Telescopes will reveal a tiny greenish disc.
• 2:49
  Another meteor shower, the Aurigids, arrives
• 2:52
  this week, active from August 28th into early
• 2:55
  September. They're usually modest, maybe 10 streaks
• 2:59
  per hour at their best, but they're quirky. The
• 3:02
  shower is known for sharp, unpredictable bursts.
• 3:06
  Their radiant lies in Auriga, climbing high before
• 3:09
  dawn. So the best time to watch is the final
• 3:12
  hours of darkness on Friday and Saturday morning.
• 3:16
  With only a slim crescent moon, the sky is yours.
• 3:20
  Now let's wander away from the summer triangle
• 3:23
  and dip into some lesser traveled constellations
• 3:26
  you can see this month. Lacerda the lizard is
• 3:30
  a faint zigzag north of Cygnus, often overlooked.
• 3:35
  Its pattern is delicate, more a whisper than
• 3:37
  a shout. But sweep binoculars through and you'll
• 3:41
  stumble across the open cluster NGC 7243, a loose
• 3:47
  scattering of stars that looks like a spilled
• 3:49
  box of jewels. Lacerda was only added to the
• 3:54
  official sky maps in the 17th century, a relative
• 3:57
  newcomer compared to the ancient Greek constellations.
• 4:02
  Aquarius, the water bearer, sits lower in the
• 4:05
  south, sprawling and hard to trace. In mythology,
• 4:09
  Aquarius pours the life -giving waters onto the
• 4:12
  Earth, but for observers it hides treasures of
• 4:16
  a different sort. Look for the globular cluster
• 4:19
  M2, a dense ball of stars about 37 ,000 light
• 4:24
  -years away, so bright that even small telescopes
• 4:28
  can resolve its grainy edges. The ancients saw
• 4:32
  Aquarius as a bringer of floods. Astronomers
• 4:35
  see him as a keeper of starry vaults. And then
• 4:40
  there's Capricornus, the sea goat, straddling
• 4:43
  myth's line between land and water. To the eye,
• 4:47
  it's a pair of shallow triangles, almost like
• 4:50
  a sideways smile, low in the southern sky. In
• 4:54
  lore, the sea goat is tied to Pan. who leapt
• 4:58
  into the Nile to escape a monster, half transformed
• 5:01
  into a fish. Through the eyepiece, Capricornus
• 5:05
  is a playground of doubles and patterns, a geometry
• 5:09
  lesson written in stars. Scan slowly and you'll
• 5:13
  find the planet Saturn parked here this season,
• 5:16
  the mythic goat, sharing the stage with the Lord
• 5:19
  of the Rings. These constellations may not command
• 5:23
  the same fame as Orion or Scorpius, but they
• 5:27
  reward patient eyes with quiet wonders. You may
• 5:31
  have heard last week that a new moon has been
• 5:33
  discovered around Uranus, thanks to careful observations
• 5:37
  by the James Webb Space Telescope. This moon
• 5:41
  is only about six miles across, which made me
• 5:45
  wonder, is it possible to walk around it? That's
• 5:49
  coming up after the break. Stay with us. Welcome
• 6:03
  back! Astronomers have just added another body
• 6:06
  to Uranus's family tree, a tiny moon barely 6
• 6:11
  miles across whirling around the planet in less
• 6:14
  than 10 hours per orbit. That bumps the official
• 6:18
  moon count for Uranus to 29. The little moon
• 6:22
  is currently only known by its placeholder name,
• 6:26
  S -2025U1. But in keeping with tradition, it'll
• 6:31
  possibly be given a literary name, perhaps a
• 6:35
  character from Shakespeare or Alexander Pope.
• 6:38
  The discovery was made with the James Webb Space
• 6:42
  Telescope with its jaw -dropping sensitivity
• 6:44
  and ability to view the near -infrared. The new
• 6:48
  moon was spotted tucked within Uranus's inner
• 6:51
  ring system, a region previously blind to Voyager
• 6:55
  2 and Hubble. It's kind of like spotting a pebble
• 6:59
  from a hundred miles away. Uranus already has
• 7:03
  a wonderfully eccentric entourage. There are
• 7:07
  the five big rounded moons, Titania, Oberon,
• 7:11
  Ariel, Umbriel, and Miranda. These are strange
• 7:15
  places carved by canyons, cliffs, and perhaps
• 7:19
  hiding briny underground seas. Then there's a
• 7:23
  swarm of smaller inner moons that shepherd the
• 7:26
  planet's delicate rings, and even more distant
• 7:29
  irregular satellites looping in eccentric orbits.
• 7:33
  Voyager 2 gave us our first and only close -up
• 7:36
  look back in 1986, discovering many of these
• 7:40
  worlds in a single flyby. Since then, telescopes
• 7:44
  have slowly filled in the roster. But this new
• 7:48
  web find fascinates me because of its size. Normally,
• 7:52
  when we're talking about topics in astronomy,
• 7:55
  we're measuring objects that are incomprehensible
• 7:57
  in size and scale. We often need to resort to
• 8:01
  exponents, 10 to some power, to describe distances,
• 8:06
  mass, and so on. For example, something gigantic,
• 8:10
  like the Milky Way galaxy, has a diameter around
• 8:13
  10 to the 24th power in meters. That's a 1 followed
• 8:18
  by 24 zeros, a nearly incomprehensible number.
• 8:23
  But this newly discovered moon is really tiny
• 8:26
  in a way that makes it relatable. Some of you
• 8:29
  may know that I'm a walker. I try to get out
• 8:31
  and walk every day if possible, and, in fact,
• 8:34
  one of these late -night Constitutionals planted
• 8:37
  the seed that resulted in this podcast. At just
• 8:42
  10 kilometers across, this new moon is so small
• 8:45
  you could, in theory, walk all the way around
• 8:48
  it in a few hours. The idea intrigues me, a hiker's
• 8:53
  circuit of an entire moon before lunch. The catch
• 8:57
  is, of course, gravity. Does an object this small
• 9:00
  produce enough gravity to keep an average human
• 9:03
  rooted on its surface? So we did the math, and
• 9:08
  the numbers are fascinating. Let's take a look
• 9:11
  at some figures, and just know these are estimates.
• 9:15
  The new moon is only about 10 kilometers across,
• 9:18
  or roughly 6 miles. That means a radius of around
• 9:22
  5 ,000 meters. If it's made of dark, icy or rocky
• 9:27
  material like Uranus's other inner moons, perhaps
• 9:31
  we can estimate the density around 1200 to 1800
• 9:35
  kg per cubic meter. That means its surface gravity
• 9:40
  works out to roughly 0 .00017 or thereabouts
• 9:46
  to 0 .00026 g. That's around 4 ,000 to 6 ,000
• 9:53
  times weaker than Earth's gravity. On Earth,
• 9:58
  gravity is a firm tug. On S -2025U1, it's practically
• 10:03
  a whisper. Surface gravity would be about 2 ten
• 10:07
  -thousandths of Earth's. Put another way, if
• 10:10
  you weigh 180 pounds here, you'd weigh less than
• 10:14
  an ounce there. The escape velocity, that's the
• 10:18
  speed you need to break free entirely, is only
• 10:21
  around 10 miles per hour. That's a hard jog.
• 10:26
  Trip and shove off too forcefully, and you wouldn't
• 10:28
  come down, you'd be in orbit for a moment and
• 10:31
  likely drifting away into space. So, would walking
• 10:36
  even work? Well, not in the traditional sense.
• 10:40
  Each step would act more like a little launch.
• 10:43
  You'd move in slow arcs, spending most of your
• 10:46
  time hovering above the surface before settling
• 10:49
  back down. To stay grounded, you'd need a tether,
• 10:53
  or something you can use to stay connected to
• 10:55
  the ground, kind of like an ice climber using
• 10:58
  a pick on a slippery slope. With care, you could
• 11:02
  shuffle around, but it would feel like spelunking
• 11:05
  on a giant trampoline in slow motion. Like the
• 11:09
  Earth's moon, the new Uranian moon is tidally
• 11:12
  locked, so it spins only once every time it orbits
• 11:16
  Uranus, about every 9 .6 hours. So at the equator,
• 11:22
  the ground slides under you at around 2 miles
• 11:25
  per hour. That slightly reduces effective gravity
• 11:29
  and escape speed at the equator by 5 to 10 percent.
• 11:33
  For comparison, Mars's tiny moon, Deimos, which
• 11:37
  is a bit larger than this object, has an escape
• 11:40
  speed around jogging pace. People often point
• 11:43
  out you can almost jump to orbit. This new moon
• 11:46
  is in that same ballpark. There's another factor
• 11:50
  at play here, and that's the tidal forces of
• 11:53
  Uranus itself. If you're trying to walk on the
• 11:56
  side of the moon facing Uranus, things get a
• 11:59
  little ticklish. You'd be even floatier, thanks
• 12:02
  to the massive influence of Uranus, which steals
• 12:05
  about a quarter of your already light weight.
• 12:08
  You won't be yanked into space while you're standing
• 12:10
  still, but a gentle hop could send you flying.
• 12:14
  I hope you enjoyed this little thought experiment,
• 12:17
  or daydream, really. There's something beautifully
• 12:20
  peculiar about Uranus. It's a sideways spinning
• 12:24
  planet. hiding possible oceans and ring moon
• 12:27
  chaos that defies typical orbits. Now Webb has
• 12:32
  shown us that Uranus contains even more secrets
• 12:35
  and reminds us that the solar system is a lot
• 12:37
  less static than we sometimes think. If the stars
• 12:45
  spoke to you this week or if a question's been
• 12:48
  on your mind, I'd love to hear it. Visit our
• 12:50
  website, StarTrails .Show, where you can contact
• 12:54
  me and explore past episodes. Be sure to follow
• 12:57
  us on Blue Sky and YouTube. Links are in the
• 13:01
  show notes. Until we meet again beneath the stars,
• 13:04
  clear skies everyone.