TGT #25C - The Star Cluster the Sun is In - Astronomical Teachniques - Finding the Ecliptic
TGT 2/15/25: Sky Planning Calendar: Using the Planets to Find the Sun's Sky Path; TCA: Three Kinds of Demonstrations for Astronomy Education; This Just In: The Ursa Major Group
Cover Photo - The Ursa Major in the Ursa Major Group
In This Issue:
Cover Photo — The Ursa Major in the Ursa Major Group
Welcome to Issue #25C!
This Just In —
* Close By and Moving StarsSky Planning Calendar —
* Moon-Gazing - Mostly Lunar Quiet….
* Observing—Plan-et - Locating the Ecliptic!
TCA — Astronomical Teachniques
Astronomy in Everyday Life — Round and Flat
Welcome to The Galactic Times Newsletter-Inbox Magazine #25C!
Greetings, Galactic Timers!
We are doing a rather educationally oriented issue. Except for the This Just In column, where we talk about one feature we can see in the sky with surprising science, the Big Dipper, we feature articles that emphasize classroom or public outreach materials. In the Sky Planning Calendar, TGT shows how to map out the Ecliptic in the night sky. In TCA (Towards Cosmic Awareness), a bunch of ‘demonstrations’ and teaching tools as an Astronomical Teachniques feature. Even the Astronomy in Everyday Life column, which came off of a Facebook post, can function as a Teachnique.
Holding one more ‘teachnique’ for next issue, on Eclipses, to go along with the Lunar Eclipse article planned.
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Enjoy!
Publisher — Dr. Larry Krumenaker Email: newsletter@thegalactictimes.com
This Just In
Close By and Moving Stars
Within a 100 parsec, 326 light-year bubble around the Sun are found gas and dust clouds and a whole lot of small stars with a few larger ones. The Sun may be a single star but surprisingly it lives inside a star cluster. It doesn’t belong to it; it isn’t the cluster it came from when it was fresh out of its stellar nursery. This one is passing by and over and around us. It is named for its most prominent, if not brightest, members; it is the Ursa Major Moving Group. Some of them prominently form the Big Dipper asterism. The star at the end of the handle and the top stars of the front of its bowl are there by coincidence.
The UMa Group, as it is abbreviated, is young, only 400 million years old. That age is derived by measuring the amount of lithium in the stellar spectra, those that exist. Many have not yet been so examined. There are at least three exoplanets among the stars in the Group. At least one is Earth-sized but it orbits closer to its star than the star’s habitable zone. In Earth time, that’s when planets develop atmospheres and surface crusts.
There are at least 1800 possible members of the Group, as observed by measuring stars’ proper motions—the motion across the sky—and their radial velocities—the velocities towards or away from us. Those with the same general values are presumed to be part of the cluster. Nearly 200 appear to be white dwarf stars. These are most valuable for determining the cluster’s age, and confirming that 400 Myr age.
Oddly, the 400 Myr age is not consistent with some of the white dwarfs. There’s a bunch centered around 600 Myr. What is not clear is if these are from a different starting point of cluster evolution, or if there is a second, co-moving cluster within the larger group. [Clark et al., University of Wisconsin, iposter at AAS January meeting.]
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Any knowledgeable astronomer, professional or amateur, should be aware that the volume near to the Sun consists of very very few bright stars, such as Spica for example. The vast majority of objects consist of the coolest stars, M-dwarfs, and even cooler L-type dwarfs, sometimes called brown dwarfs, objects not hot enough to indulge in nuclear fusion in their cores but shine largely in the infrared because of the heat from their cooling gases.
How many are there within a particular distance? Closer in further than the Ursa Major Group, researchers Loritsch et al of the University of California, San Diego are examining the bubble only 20 parsecs (roughly 64 light years) in size. Within that zone are counted around 3600 such objects. An earlier survey indicates that the general galactic population should be 70% these two kinds of cool objects. These stars are mostly less than 8% the mass of the Sun and are rich sources of molecules.
It’s a very cold bubble out there….
Sky Planning Calendar
Moon-Gazing
Moon passages by a star, planet or deep sky object are a good way to find a planet or other object if you’ve never located it before.
February 17 The Moon not only is its smallest apparent size today, being at Apogee, but it is also a mere one-third of a degree South of the bright spring blue spring star Spica.
February 20 Last Quarter Moon.
February 21 In the early AM hours, the Moon passes 0.4-degrees from the red giant star Antares.
February 27 New Moon.
February 28 The Moon-planet activity is all in the evening sky and now that the one-day-old Moon is also there, look for Mercury 0.4-degrees (just under the Moon’s apparent size, too) North (right) of the Moon. It will not be easy to the unaided eye; use binoculars.
Observing---Plan-et
==Use The Planets to Trace the Ecliptic!==
==Mercury Enters the Evening as Saturn Leaves It==
We have a nice last chance to see the path of the Ecliptic in the sky! Starting in early twilight, spot brilliant Venus in the West (and if you can, locate Mercury and Saturn below it near that horizon). Draw a line roughly towards the top of the sky (in the Northern mid-latitudes) to get to bright Jupiter. That not-quite-as-bright red star below it -South- isn’t Mars but Aldebaran, the eye of Taurus the Bull. Continue the line from Venus to Jupiter to the east and pick up the actual Red Planet, Mars. You have now traced the path of the Sun through the constellations, the aforementioned Ecliptic, and which is actually a reflection of our Earth’s orbital motion and plane. Mars is in Gemini, Venus in Pisces. Note that being in the constellation of (fill in the blank) doesn’t mean it is in the sign of the same name. In fact, due to precession—the top-like wobbling motion of the Earth’s axis—the Zodiac constellations have all shifted westward along the Ecliptic from when they were created thousands of years ago. You have only one chance in seven of having your sign match your constellation now. Well, if they can’t get the present right astronomically, how can some people claim to figure out what your future will be…..
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Mercury sets at least 45 minutes after the Sun goes down starting on the 21st, so you have some time in twilight to actually spot it low in SSW horizon. It has a conjunction (a meetup) with Saturn, not quite 2-degrees apart, on the 25th but it will be a bit difficult. Binoculars will help unless you’ve got real clear horizons and a dark environment (i.e. few if any street and commercial lights in your area). Mercury will be the brighter by far and the the right of Saturn. Use brilliant Venus to find Mercury/them as it/they will be directly below Venus.
Speaking of Venus, our sister world is riding high and bright….but it is turning on its (her?) heels and heading back into the warmth of the solar glare. It reaches a stationary point at month’s end, still setting an hour after twilight ends, but it begins then a rapid dive into the solar glare. Look now because in a month it will be gone from the evening sky.
A telescope or even binoculars can show Venus’ exquisite crescent shape, nearly 1’ (one minute of arc) in size (most people can resolve things in the sky at about 2’) and a mere 14% wide and shrinking.
Mars is bright but continues to fade as the Earth increases its distance from the Red Planet. It is stationary, not moving westward any more on the 24th. It then resumes its normal eastward direction amongst the stars.
Jupiter rules the evening sky, but sets not much after midnight. Where will its Moons be found this night? See the simulation story below.
Saturn passes the evening twilight baton to Mercury as the second largest world sinks into the solar glare. On the last day of February it sets about 40 minutes after Sunset, pretty much the last time any planet can be spotted. It has a brief conjunction with Mercury on the 25th, see above.
TCA-Astronomical Teachniques
Jupiter In A Classroom
Ed Marici of Villanova University reported at the AAS in January that they have developed a new Web-based simulation of Jupiter and its moons. Find it at labs.ast.villanova.edu .
Classroom Demos - Analogies, Visual Metaphors, and Literal Demonstrations
My one-time classmate and excellent astronomy education and history professor Dr. Thomas Hockey of the University of Northern Iowa wants to clarify how we do astronomy demonstrations in labs and classrooms. As he wrote in his iposter at the AAS meeting, astronomy is the science of the remote. Unlike physics or chemistry or other sciences we can’t bring the real universe into the classroom and teach with the actual objects. The term ‘demonstrations’ he feels is far too broad and unrealistic. He proposes to divide the genre into three kinds: Analogies, Visual Metaphors, and Literal Demonstrations. To, um, demonstrate them he provided some samples.
Analogies
The above example is relevant to the Galilean Moons. The squeeze ball represents Io; pulling on the sponge ball represents what happens when Jupiter’s tidal gravitational forces changes the shape of the moon. The ice cube tray, when filled with water and then frozen, shows that ice expands and emerges out of its constraining shape. Such activity occurs on Ganymede where old crust and new crust compete and crack the surface.
You can buy a globe of just about every planet, but asteroids? No. They aren’t spherical, but if you can find one regular globe of the correct size, with its axis holders embedded in the semi-circular frame, you can show how asteroids are not spherical but still rotate by using potatoes. [In an earlier article in The Classroom Astronomer we also showed a demonstration of how the recording of reflected light off an irregularly shaped potato gives a light curve that can be used to determine the shape of the asteroid.]
Visual Metaphors
We teachers have often used the metaphor of campers around a fire for explaining how we get heat from the Sun to Earth. But that’s not really accurate physically and the usual way humans get warmer or colder is to move towards or away from the fire. But Earth is warmer when we are at aphelion, farthest from the Sun (at least in the Northern Hemisphere) so how does that really happen? Answer—an electric furnace, preferably one that simulates with fire images as well as heat, but not allow students to move from their seats. Hands or at least fingertips but not where fingers connect to the palm get more heat when tilted towards the furnace than when perpendicular to the furnace.
Literal Demonstrations
Refraction. ‘Nuff said.
Astronomy in Everyday Life
Along the lines of the TCA items…..
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