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Stars 101: The Building Blocks of the Cosmos · Star Trails: From Backyard Astronomy to Cosmic Wonder

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  Howdy Stargazers, and welcome to this episode of Star Trails.
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  I'm Drew, and I'll be your guide to the night sky for the week starting January 19th through
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  the 25th.
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  This week we're getting back to the basics with a look at the building blocks of the
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  night sky, stars, where they come from, what they are, their diverse colors and types,
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  and how the night sky changes with the seasons.
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  Of course, we'll look at what's in the night sky this week, so let's get started.
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  Hopefully you managed to catch last week's stunning full moon occultation of Mars.
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  Last Tuesday started as a gloomy cloudy day here in my hometown, so I didn't get my
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  hopes up.
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  But by 7pm the clouds were rolling out, leaving a hazy but workable night sky.
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  Mars was visible below the moon.
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  By 9pm I had a clear view of the moon, and it was almost painfully bright in my 11x70
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  binoculars.
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  By then Mars was exactly below the moon, and because the moon was so bright it washed out
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  Mars, meaning you'd need a scope or binoculars to even see it.
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  I found a comfortable chair in my backyard and braced my elbows against the chair arms
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  to steady my binoculars, and then watched as Mars slowly approached the moon.
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  It finally vanished behind the moon's south pole around 9.12pm Eastern time.
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  I went back outside around 10pm and waited until Mars emerged from behind the moon's
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  northeast edge around 10.15pm, barely visible as a tiny dot and finally separating from
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  the moon.
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  Across town a few miles away my friend Stuart was observing the phenomenon with his 10 inch
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  Dopsonian reflector, and reported being able to see ice caps on Mars.
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  Overall it was a stunning night of stargazing and the first time I've witnessed an occultation
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  of a planet.
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  The moon is in a waning gibbous phase at the start of the week but shrinking to a crescent
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  by week's end, bringing darker skies for tracking down those deep sky objects.
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  The planets haven't shifted much in a week with Venus still dominating the twilight and
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  early evening in the southwest.
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  Saturn is still dancing nearby.
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  Jupiter is the brightest object in the southern sky, rising high in the evening.
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  Mars, having just reached opposition last week, remains a striking red object in Gemini,
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  lining up with the bright stars, caster and Pollux.
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  Winter's famous constellations like Orion, Taurus, and Gemini are still up there, but
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  here are a few others you might enjoy.
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  Look almost overhead if you're in mid-Northern latitudes to locate Cassiopeia.
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  It's a distinctive W shape of bright stars.
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  Just below Cassiopeia, Perseus arcs across the sky.
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  This constellation boasts several star clusters, including the famous double cluster NGC 869
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  and NGC 884.
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  A pair of binoculars reveals these two close-knit clusters glimmering with countless stars.
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  High in the east to southeast after sunset, Auriga is marked by its brightest star, Capella.
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  Within Auriga's boundaries lie three lovely open clusters, M36, M37, and M38, all visible
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  in a small telescope or even binoculars under dark skies.
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  Let's get really basic here.
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  Of course, we all know astronomy is the study of celestial objects, but translated from
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  its Greek roots, Aster and Nomiya, it literally means name stars.
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  In this Astronomy 101 segment, we're taking a very top-level look at stars.
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  There's so many of them when we look up that it's easy to overlook how fascinating they
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  are.
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  In fact, if it weren't for stars, we wouldn't exist.
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  More on that later.
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  A star is essentially a colossal, luminous sphere of gas, mostly hydrogen and helium,
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  held together by its own gravity.
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  At its core, nuclear fusion fuses hydrogen into helium, releasing immense energy that
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  radiates outward and gives the star its distinctive glow.
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  Stars form in nebula, also called stellar nurseries.
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  These are giant clouds of gas and dust where matter collapses under gravity.
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  The star's life cycle depends heavily on its initial mass.
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  All to medium stars, like our sun, can live for billions of years, while massive stars
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  burn through their fuel rapidly and often end in dramatic supernova explosions.
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  On a clear dark night, you can typically see a few thousand stars with the naked eye, but
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  all of them lie within our own Milky Way galaxy, which contains hundreds of billions of stars.
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  Though that number is staggering, our eyes aren't sensitive enough to resolve stars
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  in other galaxies.
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  The Andromeda galaxy, for instance, is visible from Earth with the naked eye under very dark
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  skies, but only the most recent observations from space telescopes such as the James Webb
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  scope have been able to resolve stars outside the Milky Way.
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  Stars classify stars into different spectral types, O, B, A, F, G, K, and M, arranged from
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  hottest and most massive to coolest and more common.
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  O and B stars tend to be extremely hot, luminous, and blue-white in appearance.
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  A and F stars are still quite bright but slightly cooler.
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  G stars, such as our sun, are moderate in temperature and often yellowish-white.
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  K stars appear slightly cooler and more orange, while M stars are red and they're the most
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  common type, often known as red dwarves.
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  The variety of colors you see among stars ties directly to their surface temperatures.
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  Hotter stars can appear blue-white, while cooler stars will glow orange or red.
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  This color, or spectral signature, reveals essential details about a star's life stage
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  and composition.
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  Blue or white stars generally burn through their hydrogen quickly because of their higher
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  mass and temperature, whereas cooler red stars can have extraordinarily long lifespans, sometimes
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  lasting tens of billions of years.
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  When you scan the sky on any given night, you'll notice that some stars stand out more than
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  others.
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  This difference in brightness primarily comes from two factors, the star's intrinsic luminosity
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  and its distance from Earth.
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  Intrinsically luminous stars are simply more energetic because they're either larger,
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  hotter, or both, which makes them shine with greater intensity.
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  A star's distance from this also plays a crucial role because even a powerful star will appear
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  fainter if it lies far enough away.
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  Astronomers distinguish between apparent magnitude, which measures how bright a star appears to
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  us on Earth, and absolute magnitude, which describes how bright a star would appear if
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  it were placed at a standard distance of about 32.6 light-years.
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  Using both types of magnitude helps us separate the star's true power from the effects of
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  distance.
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  Over millennia, cultures around the world have observed patterns in the sky and woven
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  them into myths or used them for practical navigation.
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  These patterns became constellations, and modern astronomy officially recognizes 88 of them,
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  each marking a specific region of the celestial sphere.
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  However, not every familiar pattern you see is an official constellation.
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  Astorisms are smaller or more informal arrangements of stars that span or subdivide constellations
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  and serve as convenient guideposts when learning the night sky.
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  People often use them to orient themselves, locate specific constellations, and teach newcomers
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  the basics of stargazing.
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  A great example of an asterism is the Big Dipper, which is actually part of the larger
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  constellation Ursa Major.
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  One of the continually fascinating aspects of stargazing is the way the sky changes from
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  one season to the next.
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  As Earth orbits the Sun over the course of a year, the night side of our planet faces
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  different regions of space.
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  This means the stars you see in the sky will shift every few months.
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  Even well-known constellations such as Scorpius and Sagittarius become prominent during summer
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  evenings in the northern hemisphere, while others like Cygnus or Lyra might move closer
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  to the western horizon.
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  In winter, a different set of constellations takes center stage.
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  Greek letters are used to designate stars according to a system introduced by the German
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  astronomer Johann Baer in the early 17th century.
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  A method often referred to as the Baer designation.
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  In this system, each star within a constellation is assigned a Greek letter, alpha, beta, gamma,
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  and so on, paired with the constellation's Latin name.
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  Traditionally, the brightest star in the constellation is labeled alpha, the second
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  brightest is beta, and so forth.
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  Although this rule isn't always perfectly followed due to variations in historical brightness
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  estimates and observational data.
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  For example, in the constellation Lyra, the brightest star is alpha, Lyrae, better known
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  as Vega, while the second brightest is beta, Lyrae.
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  This scheme helps astronomers refer to specific stars in a structured way.
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  Other star naming conventions exist, but Baer's Greek letter labels are among the most recognizable
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  to casual and seasoned stargazers alike.
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  Stars move relative to one another over very long periods.
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  Given enough time, the familiar outlines of constellations will morph into completely
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  different shapes.
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  Right now, we see the Big Dipper as a ladle-like figure, but in a hundred thousand years, those
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  same stars will no longer line up in the same way.
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  In our last episode, we covered the Ecliptic, which is the plane of the Earth's orbit around
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  the Sun.
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  The Ecliptic is like a celestial highway in the sky because the moon, sun, and planets
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  line up along it.
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  The group of constellations known as the Zodiac also lies along the Ecliptic.
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  There are 12 constellations in the Zodiac, 13 if you include Ophiuchus, and their names
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  will probably be familiar to you, Capricorn, Virgo, Ares, and so on.
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  Because the Sun appears to move through these constellations over the course of a year,
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  the Zodiac became a focus of ancient astrology.
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  If you're in the Northern Hemisphere, you'll notice the entire sky seems to rotate around
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  one point near the North.
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  That point is marked by Polaris, also known as the North Star, which lies near the North
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  celestial pole where Earth's axis of rotation meets the sky.
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  Because Polaris is aligned with our planet's axis, it appears almost stationary to us,
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  while every other star, thanks to Earth's rotation, rises in the east and sets in the
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  west.
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  Conservers in the Southern Hemisphere don't have a single bright star near the South celestial
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  pole, but they can still see the same circular rotation around a pivot point in the southern
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  sky.
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  Here's an interesting fact.
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  The North Star hasn't always been Polaris, and it won't always be.
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  Earth's axis slowly wobbles over a cycle of about 26,000 years, a phenomenon called
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  precession.
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  Because of this, the star closest to the North celestial pole changes over millennia.
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  Thousands of years ago, the star Thuban in the constellation Draco was the North Star,
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  and in about 12,000 years, Vega in the constellation Lyra will take that title.
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  Before we wrap this up, here are some other interesting notes about stars.
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  One, stars don't really twinkle. The atmospheric turbulence around Earth causes the starlight
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  to bend and makes it look as though stars are flickering.
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  Seen from space, without an atmosphere in the way, stars appear steady.
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  Planets also show less twinkling because their discs are larger in apparent size, so the
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  effect of atmospheric distortion averages out more smoothly.
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  Two, looking at stars is like stepping into a cosmic time machine.
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  Because light takes years to travel, when you see a star that's, say, 100 light years
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  away, you're actually seeing it as it was 100 years ago.
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  For nearby stars, this effect is slight, but for very distant objects, you're peering
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  back into events that happened thousands or even millions of years ago.
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  Three, some stars spin fast enough to flatten themselves.
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  Certain stars rotate at such high speeds that they appear more oblate, meaning flattened
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  at the poles and bulging at the equator.
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  For example, Altair in the constellation Aquila spins so rapidly that its equatorial diameter
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  is significantly larger than its polar diameter.
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  Four, the biggest stars we know are mind-bogglingly large.
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  While our Sun has a diameter of roughly 1.4 million kilometers, a star like U.I.
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  Scudy is estimated to have a diameter of more than 1,700 times that of the Sun.
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  If you placed U.I.
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  Scudy where our Sun is, it would extend far beyond the orbit of Jupiter.
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  And finally, you may have heard the famous Carl Sagan quote, we're made of star stuff.
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  And that's because heavy elements like carbon, oxygen, and iron are forged inside stars and
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  spread throughout space when those stars die, especially in supernova explosions.
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  That means the atoms in your body were once part of an ancient star, and that's quite
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  a humbling notion when looking up at the night sky.
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  If you found this episode helpful, let me know and feel free to send in your questions
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  and observations.
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  The easiest way to do that is by visiting our website, startrails.show.
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  This is also a great way to share the show with friends.
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  Until next time, keep looking up and exploring the night sky.
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  Dear skies, everyone.