1 00:00:00,000 --> 00:00:12,640 Howdy Stargazers and welcome to this episode of Star Trails. 2 00:00:12,640 --> 00:00:18,520 I'm Drew and I'll be your guide to the night sky for the week starting January the 12th 3 00:00:18,520 --> 00:00:20,360 through the 18th. 4 00:00:20,360 --> 00:00:27,000 I'm really excited this week because a spooky phenomenon awaits us on January 13th. 5 00:00:27,000 --> 00:00:33,800 The full, wolf moon will occult the planet Mars, causing it to disappear for about an 6 00:00:33,800 --> 00:00:34,800 hour. 7 00:00:34,800 --> 00:00:41,760 We'll explore why that happens and why we sometimes see eclipses and parades of planets. 8 00:00:41,760 --> 00:00:43,600 It's all connected. 9 00:00:43,600 --> 00:00:48,040 In the second half of the episode I'll share some facts about the solar system that you 10 00:00:48,040 --> 00:00:50,040 may not have heard before. 11 00:00:50,040 --> 00:00:56,320 For example, did you know Jupiter doesn't exactly orbit the sun like the other planets? 12 00:00:56,320 --> 00:00:59,720 Click around and I'll tell you why. 13 00:00:59,720 --> 00:01:06,080 This week is shaping up to be a fun one for stargazers, so let's get started. 14 00:01:06,080 --> 00:01:11,320 The moon will be the main event this week as it waxes towards being full on January 15 00:01:11,320 --> 00:01:12,920 13th. 16 00:01:12,920 --> 00:01:17,400 This month's full moon is traditionally called the wolf moon. 17 00:01:17,400 --> 00:01:23,800 In January's depths of winter, wolves were often heard howling outside villages, inspiring 18 00:01:23,800 --> 00:01:26,200 this evocative name. 19 00:01:26,200 --> 00:01:31,880 This luminous full moon will dominate the sky, making it a perfect companion for moon-lit 20 00:01:31,880 --> 00:01:34,560 strolls. 21 00:01:34,560 --> 00:01:40,520 Also on the 13th, a rare lunar occultation of Mars will occur, where the moon passes 22 00:01:40,520 --> 00:01:45,000 in front of Mars, temporarily hiding it from view. 23 00:01:45,000 --> 00:01:51,960 Observers on the east coast can expect to see Mars disappear between 9pm and 9.30pm, 24 00:01:51,960 --> 00:01:54,880 reappearing about an hour later. 25 00:01:54,880 --> 00:01:58,640 The west coast will see this event around 6pm. 26 00:01:58,640 --> 00:02:04,640 Be sure to consult with a stargazing app like Stellarium or Sky Safari to learn the exact 27 00:02:04,640 --> 00:02:09,120 time when you can see this phenomenon in your area. 28 00:02:09,120 --> 00:02:13,460 By weeks end, the moon will have dwindled to nearly a third quarter moon with a little 29 00:02:13,460 --> 00:02:16,800 more than half of the surface illuminated. 30 00:02:16,800 --> 00:02:22,000 If Mars seems a little brighter this week, it's because the red planet reaches opposition 31 00:02:22,000 --> 00:02:29,000 on January 15, meaning it will be at its brightest and most prominent size for the year. 32 00:02:29,000 --> 00:02:33,960 Look for its reddish hue in the east in the constellation Gemini. 33 00:02:33,960 --> 00:02:39,040 It's visible all night as it makes its way west before dawn. 34 00:02:39,040 --> 00:02:44,920 Venus and Saturn will appear exceptionally close to each other on January 17 and 18, 35 00:02:44,920 --> 00:02:50,960 a conjunction visible in the southwestern sky shortly after sunset. 36 00:02:50,960 --> 00:02:55,680 Venus, the brighter of the two, will guide you to Saturn, just slightly to the left and 37 00:02:55,680 --> 00:02:57,880 above Venus. 38 00:02:57,880 --> 00:03:02,320 Jupiter is currently shining brightly in the constellation Taurus. 39 00:03:02,320 --> 00:03:07,000 Look for it in the southeast sky between Orion and the Pleiades. 40 00:03:07,000 --> 00:03:11,200 It will be the brightest object in that portion of the sky. 41 00:03:11,200 --> 00:03:15,560 Mercury will be a morning star this week, but fairly elusive. 42 00:03:15,560 --> 00:03:25,840 Look for it on the eastern horizon just before dawn. 43 00:03:25,840 --> 00:03:32,400 In our last episode, I told you how to locate Orion by its three prominent belt stars, and 44 00:03:32,400 --> 00:03:39,880 we journeyed through Taurus, home of the bright star Aldebaran and the Hyades star cluster. 45 00:03:39,880 --> 00:03:44,240 Let's take a look at another constellation nearby, Gemini. 46 00:03:44,240 --> 00:03:50,800 To the northeast of Orion, Gemini's twin stars, Castor and Pollux, are prominent. 47 00:03:50,800 --> 00:03:56,920 The story of these twins is one of loyalty, love, and sacrifice. 48 00:03:56,920 --> 00:04:01,800 According to mythology, Castor and Pollux were said to be the sons of Lita, a mortal 49 00:04:01,800 --> 00:04:08,160 woman, and either her mortal husband, King Tendarius of Sparta, or the god Zeus, who 50 00:04:08,160 --> 00:04:12,200 seduced Lita in the form of a swan. 51 00:04:12,200 --> 00:04:17,680 Pollux was considered immortal because Zeus was his father, while Castor, being the son 52 00:04:17,680 --> 00:04:20,640 of Tendarius, was mortal. 53 00:04:20,640 --> 00:04:25,640 Despite their different parentage, Castor and Pollux were inseparable and renowned for their 54 00:04:25,640 --> 00:04:26,640 adventures. 55 00:04:26,640 --> 00:04:31,920 Together, they joined Jason and the Argonauts in their quest for the Golden Fleece. 56 00:04:31,920 --> 00:04:36,800 They were also known for their strength, bravery, and skill in battle. 57 00:04:36,800 --> 00:04:42,880 Their story takes a sorrowful turn when Castor, the mortal twin, is killed in a fight. 58 00:04:42,880 --> 00:04:49,200 Pollux, stricken with grief, begged Zeus to let him share his immortality with his brother. 59 00:04:49,200 --> 00:04:55,920 Zeus, moved by Pollux's devotion, grants his wish by transforming both brothers into 60 00:04:55,920 --> 00:05:01,320 stars, placing them together in the sky as the constellation Gemini. 61 00:05:01,320 --> 00:05:06,120 The constellation's two brightest stars represent the heads of the twins. 62 00:05:06,120 --> 00:05:12,240 They sit close together in the sky, with their bodies outlined by dimmer stars. 63 00:05:12,240 --> 00:05:19,040 Pollux is an orange giant star, slightly brighter than Castor, while Castor, a white star, is 64 00:05:19,040 --> 00:05:25,400 actually a complex system of six stars bound by gravity. 65 00:05:25,400 --> 00:05:30,640 Mars will become part of this constellation during the week, adding a bright, reddish, 66 00:05:30,640 --> 00:05:41,640 and negative 1.4 magnitude guest star to the twins. 67 00:05:41,640 --> 00:05:46,120 If you pay attention to the positions of the planets, the moon, and the sun, you might 68 00:05:46,120 --> 00:05:48,720 notice something peculiar. 69 00:05:48,720 --> 00:05:52,680 They all follow a similar path across the sky. 70 00:05:52,680 --> 00:05:57,960 For example, right now the moon, Saturn, and Venus are roughly lined up in one part of 71 00:05:57,960 --> 00:05:59,320 the sky. 72 00:05:59,320 --> 00:06:04,120 If you were to draw a line through them, that line would arc across the sky to the opposite 73 00:06:04,120 --> 00:06:08,240 horizon, passing near Jupiter and Mars. 74 00:06:08,240 --> 00:06:13,400 The line that the planets follow is the ecliptic plane. 75 00:06:13,400 --> 00:06:19,280 Our solar system is actually a relatively flat disk, with the planets orbiting the sun 76 00:06:19,280 --> 00:06:23,320 on a conceptual plane, called the ecliptic. 77 00:06:23,320 --> 00:06:28,480 Earth and the other planets' orbits are roughly aligned to the ecliptic plane. 78 00:06:28,480 --> 00:06:33,720 When we look up at the night sky, the ecliptic appears as a curved line tracing across the 79 00:06:33,720 --> 00:06:40,040 celestial sphere, marking the sun's apparent path over the course of a year. 80 00:06:40,040 --> 00:06:46,200 The planets formed from a rotating disk of gas and dust billions of years ago. 81 00:06:46,200 --> 00:06:52,560 This protoplanetary disk flattened out owing to the conservation of angular momentum, leading 82 00:06:52,560 --> 00:06:55,840 to the alignment of planetary orbits. 83 00:06:55,840 --> 00:07:01,240 While their orbits aren't perfectly aligned, each has a slight tilt, they all stay close 84 00:07:01,240 --> 00:07:03,240 to the ecliptic. 85 00:07:03,240 --> 00:07:08,840 The sun's path across the sky follows the ecliptic, as does the moon, although its orbit 86 00:07:08,840 --> 00:07:12,400 is slightly tilted relative to the ecliptic. 87 00:07:12,400 --> 00:07:18,360 When the moon and sun's apparent paths intersect, it creates a point called a node. 88 00:07:18,360 --> 00:07:22,760 These are points where solar and lunar eclipses can occur. 89 00:07:22,760 --> 00:07:28,440 As planets and the moon hover near the ecliptic, their apparent paths often intersect. 90 00:07:28,440 --> 00:07:33,640 This is why events like the Venus and Saturn conjunction, or the Mars occultation by the 91 00:07:33,640 --> 00:07:35,440 moon, occur. 92 00:07:35,440 --> 00:07:40,440 They're all traveling along the same general path in the sky. 93 00:07:40,440 --> 00:07:46,200 The idea of the ecliptic simplifies the study of celestial motions and provides a framework 94 00:07:46,200 --> 00:07:50,560 for understanding alignments and events in the sky. 95 00:07:50,560 --> 00:07:55,880 For backyard astronomers, it's a celestial highway guiding you to the planets and even 96 00:07:55,880 --> 00:08:05,880 the occasional surprise like a comet or asteroid. 97 00:08:05,880 --> 00:08:12,680 Now let's look at some weird facts related to a few of the planets in our solar system. 98 00:08:12,680 --> 00:08:17,960 Did you know a day on Mercury is longer than its year? 99 00:08:17,960 --> 00:08:23,360 Mercury takes about 88 Earth days to complete one orbit around the sun. 100 00:08:23,360 --> 00:08:24,720 That's its year. 101 00:08:24,720 --> 00:08:32,560 However, it also spins on its axis very slowly, taking about 59 Earth days to make one full 102 00:08:32,560 --> 00:08:34,840 rotation. 103 00:08:34,840 --> 00:08:40,240 This rotational period is called a sidereal day, and it's a bit different from a solar 104 00:08:40,240 --> 00:08:45,360 day which features a sunrise and sunset. 105 00:08:45,360 --> 00:08:49,880 Because of this interplay between orbit and rotation, from the perspective of someone 106 00:08:49,880 --> 00:08:57,640 standing on Mercury's surface, the time from one sunrise to the next is roughly 176 Earth 107 00:08:57,640 --> 00:08:59,640 days long. 108 00:08:59,640 --> 00:09:07,080 In other words, one solar day on Mercury lasts almost twice as long as a Mercuryan year. 109 00:09:07,080 --> 00:09:13,040 This odd scheduling is due to something called a spin orbit resonance. 110 00:09:13,040 --> 00:09:18,640 Mercury is in a 3-2 resonance, meaning it rotates exactly three times about its axis 111 00:09:18,640 --> 00:09:22,520 for every two orbits around the sun. 112 00:09:22,520 --> 00:09:28,320 Spin orbit resonances happen because tidal forces from the sun lock the planet's rotation 113 00:09:28,320 --> 00:09:32,960 rate in a precise ratio to its orbital period. 114 00:09:32,960 --> 00:09:38,480 Mercury is close enough to the sun that it experiences powerful gravitational pulls, 115 00:09:38,480 --> 00:09:43,480 ensuring its spin and orbit remain locked in this unusual pattern. 116 00:09:43,480 --> 00:09:50,320 Now, let's cruise over to Venus, the hottest planet in the solar system, and one with another 117 00:09:50,320 --> 00:09:53,400 rotational quirk. 118 00:09:53,400 --> 00:09:58,520 Most planets in the solar system rotate on their axes in the same direction they orbit 119 00:09:58,520 --> 00:10:05,360 the sun, which is counterclockwise if viewed from above the sun's north pole. 120 00:10:05,360 --> 00:10:09,480 Venus, however, spins in the opposite direction. 121 00:10:09,480 --> 00:10:14,680 This is called retrograde rotation, and it means that on Venus, the sun would appear 122 00:10:14,680 --> 00:10:21,120 to rise in the west and set in the east, if you could survive long enough under its harsh 123 00:10:21,120 --> 00:10:25,800 atmospheric conditions to watch a sunset. 124 00:10:25,800 --> 00:10:31,800 No one is entirely sure why Venus rotates backward, but the leading hypotheses involve 125 00:10:31,800 --> 00:10:38,080 ancient collisions with large protoplanetary bodies, or gravitational interactions with 126 00:10:38,080 --> 00:10:40,680 the sun and other planets. 127 00:10:40,680 --> 00:10:46,880 Whatever caused this backward spin, the slow retrograde rotation of Venus contributes to 128 00:10:46,880 --> 00:10:53,440 its extreme atmospheric dynamics and bizarre day-night cycles. 129 00:10:53,440 --> 00:11:00,920 A sidereal day on Venus is 243 Earth days, making it longer than its year, which is around 130 00:11:00,920 --> 00:11:04,960 225 Earth days. 131 00:11:04,960 --> 00:11:10,200 Venus boasts the highest temperatures of any planet in our solar system, with surface temperatures 132 00:11:10,200 --> 00:11:14,420 around 860 degrees Fahrenheit. 133 00:11:14,420 --> 00:11:20,760 This extreme heat is largely due to a runaway greenhouse effect driven by its dense carbon 134 00:11:20,760 --> 00:11:23,320 dioxide atmosphere. 135 00:11:23,320 --> 00:11:30,080 The thick cloud layers trap heat very efficiently, allowing sunlight in but preventing infrared 136 00:11:30,080 --> 00:11:34,840 radiation from escaping back into space. 137 00:11:34,840 --> 00:11:40,320 Venus' clouds are filled with sulfuric acid droplets, and the resulting chemical and thermal 138 00:11:40,320 --> 00:11:44,240 environment is incredibly hostile. 139 00:11:44,240 --> 00:11:49,240 Probes that have landed on Venus, like the Soviet Venera missions, survived only a short 140 00:11:49,240 --> 00:11:55,160 time on the order of minutes to a couple of hours before succumbing to the crushing pressure 141 00:11:55,160 --> 00:11:57,120 and corrosive heat. 142 00:11:57,120 --> 00:12:03,200 Yet, this very harshness makes Venus a key laboratory for understanding the limits of 143 00:12:03,200 --> 00:12:08,760 planetary habitability and the power of greenhouse gases. 144 00:12:08,760 --> 00:12:17,360 Let's make a jump out to Jupiter, our largest planet, and an outlier for several other reasons. 145 00:12:17,360 --> 00:12:23,440 Jupiter's great red spot is an enormous storm system big enough to swallow multiple Earths. 146 00:12:23,440 --> 00:12:29,520 It's been observed continuously since at least the 1600s, making it perhaps the longest 147 00:12:29,520 --> 00:12:32,040 lived storm we know. 148 00:12:32,040 --> 00:12:37,720 While the great red spot has shrunk somewhat over recent decades, it remains a swirling 149 00:12:37,720 --> 00:12:43,560 anti-cyclone with winds topping hundreds of kilometers per hour. 150 00:12:43,560 --> 00:12:48,520 Scientists still debate why it's so stable and why it's red. 151 00:12:48,520 --> 00:12:53,040 Possible explanations range from the storm dredging up chemicals from deep in Jupiter's 152 00:12:53,040 --> 00:13:00,040 atmosphere that turn red when exposed to sunlight, to complex interactions of ammonia 153 00:13:00,040 --> 00:13:02,560 and other compounds. 154 00:13:02,560 --> 00:13:08,160 Juno spacecraft data continues to shed new light on the storm's depth and structure, 155 00:13:08,160 --> 00:13:13,720 but the great red spot remains a powerhouse of planetary meteorology, illustrating how 156 00:13:13,720 --> 00:13:17,960 different weather can be on a gas giant compared to Earth. 157 00:13:17,960 --> 00:13:21,680 Here's a strange but true tidbit. 158 00:13:21,680 --> 00:13:24,760 Jupiter doesn't orbit the Sun's center. 159 00:13:24,760 --> 00:13:31,440 It orbits a shared center of mass, the Berry Center, that actually lies outside the Sun's 160 00:13:31,440 --> 00:13:32,880 surface. 161 00:13:32,880 --> 00:13:38,080 Despite Jupiter being only a fraction of the Sun's mass, it's still so massive compared 162 00:13:38,080 --> 00:13:43,800 to the other planets that its gravitational pull is significant enough to yank the Sun 163 00:13:43,800 --> 00:13:46,400 ever so slightly off-center. 164 00:13:46,400 --> 00:13:51,560 When two bodies orbit each other, say Jupiter and the Sun, they both revolve around their 165 00:13:51,560 --> 00:13:57,200 combined center of mass, not just one body around the other. 166 00:13:57,200 --> 00:14:02,400 Because Jupiter is by far the heaviest planet in the Solar System, more than twice as massive 167 00:14:02,400 --> 00:14:08,440 as all other planets combined, the Sun-Jupiter Berry Center ends up sitting about one to 168 00:14:08,440 --> 00:14:13,000 two solar radii above the Sun's actual center. 169 00:14:13,000 --> 00:14:18,360 This might sound small on the scale of the entire Solar System, but it's enormous compared 170 00:14:18,360 --> 00:14:21,880 to how the other, lighter planets affect the Sun. 171 00:14:21,880 --> 00:14:27,520 So when you visualize Jupiter orbiting the Sun, remember that the Sun is also wobbling 172 00:14:27,520 --> 00:14:33,480 around a point in space, paying its gravitational dues to the Solar System's most massive 173 00:14:33,480 --> 00:14:36,040 planet. 174 00:14:36,040 --> 00:14:40,760 Jupiter's massive gravity doesn't just pull the Sun off-center, it also orchestrates 175 00:14:40,760 --> 00:14:44,600 a host of other dance moves throughout the Solar System. 176 00:14:44,600 --> 00:14:50,560 For instance, many astronomers refer to Jupiter as the Solar System's cosmic vacuum cleaner, 177 00:14:50,560 --> 00:14:55,720 because it deflects or captures numerous comets and asteroids that might otherwise threaten 178 00:14:55,720 --> 00:14:58,280 the inner planets. 179 00:14:58,280 --> 00:15:04,000 When a comet from the distant Kuiper Belt or O-Ork cloud ventures inward, Jupiter's strong 180 00:15:04,000 --> 00:15:09,880 gravitational field can alter the comet's trajectory significantly, sometimes flinging 181 00:15:09,880 --> 00:15:15,680 it back out of the Solar System or steering it into a collision course with itself, as 182 00:15:15,680 --> 00:15:20,960 with comet Shoemaker-Levy-9 in 1994. 183 00:15:20,960 --> 00:15:26,880 In this way, Jupiter acts as a partial shield for Earth, though it can hurl objects onto 184 00:15:26,880 --> 00:15:32,240 potentially hazardous paths, depending on the geometry of the encounter. 185 00:15:32,240 --> 00:15:37,380 Another lesser-known effect is Jupiter's role in creating gaps in the asteroid belt. 186 00:15:37,380 --> 00:15:40,880 We mentioned this in our last episode. 187 00:15:40,880 --> 00:15:46,160 Asteroids whose orbits resonate strongly with Jupiter's, for example those completing exactly 188 00:15:46,160 --> 00:15:53,160 three orbits for every one of Jupiter's, can get their orbits destabilized over time. 189 00:15:53,160 --> 00:15:58,880 This gravitational nudging carves out the so-called Kirkwood gaps, which are underpopulated 190 00:15:58,880 --> 00:16:02,680 zones in the asteroid belt. 191 00:16:02,680 --> 00:16:07,240 There are a lot more fun facts we could discuss about these and other planets, but we'll save 192 00:16:07,240 --> 00:16:09,840 those for future episodes. 193 00:16:09,840 --> 00:16:13,720 Be sure to get out this week and watch the moon occult Mars. 194 00:16:13,720 --> 00:16:18,960 And while we do have a bright moon washing out all those fainter deep-sky objects, it's 195 00:16:18,960 --> 00:16:26,920 still a great time for looking at Jupiter and Saturn through a nice telescope. 196 00:16:26,920 --> 00:16:31,400 If you found this episode helpful, let me know and feel free to send in your questions 197 00:16:31,400 --> 00:16:33,160 and observations. 198 00:16:33,160 --> 00:16:39,280 The easiest way to do that is by visiting our website, startrails.show. 199 00:16:39,280 --> 00:16:43,000 This is also a great way to share the show with friends. 200 00:16:43,000 --> 00:16:47,160 Until next time, keep looking up and exploring the night sky. 201 00:16:47,160 --> 00:17:03,640 Clear skies, everyone.