Tag Archives: Aavso

NASA Night Sky Notes: Summer Triangle Corner – Vega

Poster’s Note: One of the many under-appreciated aspects of NASA is the extent to which it publishes quality science content for children and Ph.D.’s alike. Your tax dollars help promote science! The following article was provided for reprinting by the Night Sky Network in June, 2020.

By David Prosper and Vivian White

If you live in the Northern Hemisphere and look up during June evenings, you’ll see the brilliant star Vega shining overhead. Did you know that Vega is one of the most studied stars in our skies? As one of the brightest summer stars, Vega has fascinated astronomers for thousands of years.

Vega is the brightest star in the small Greek constellation of Lyra, the harp. It’s also one of the three points of the large “Summer Triangle” asterism, making Vega one of the easiest stars to find for novice stargazers. Ancient humans from 14,000 years ago likely knew Vega for another reason: it was the Earth’s northern pole star! Compare Vega’s current position with that of the current north star, Polaris, and you can see how much the direction of Earth’s axis changes over thousands of years. This slow movement of axial rotation is called precession, and in 12,000 years Vega will return to the northern pole star position. Bright Vega has been observed closely since the beginning of modern astronomy and even helped to set the standard for the current magnitude scale used to categorize the brightness of stars. Polaris and Vega have something else in common, besides being once and future pole stars: their brightness varies over time, making them variable stars. Variable stars’ light can change for many different reasons. Dust, smaller stars, or even planets may block the light we see from the star. Or the star itself might be unstable with active sunspots, expansions, or eruptions changing its brightness. Most stars are so far away that we only record the change in light, and can’t see their surface.

NASA’s TESS satellite has ultra-sensitive light sensors primed to look for the tiny dimming of starlight caused by transits of extrasolar planets. Their sensitivity also allowed TESS to observe much smaller pulsations in a certain type of variable star’s light than previously observed. These observations of Delta Scuti variable stars will help astronomers model their complex interiors and make sense of their distinct, seemingly chaotic, pulsations. This is a major contribution towards the field of astroseismology: the study of stellar interiors via observations of how sound waves “sing” as they travel through stars. The findings may help settle the debate over what kind of variable star Vega is. Find more details on this research, including a sonification demo that lets you “hear” the heartbeat of one of these stars, at: bit.ly/DeltaScutiTESS

Interested in learning more about variable stars? Want to observe their changing brightness? Check out the website for the American Association of Variable Star Observers (AAVSO) at aavso.org. You can also find the latest news about Vega and other fascinating stars at nasa.gov.

Vega possesses two debris fields, similar to our own solar system’s asteroid and Kuiper belts. Astronomers continue to hunt for planets orbiting Vega, but as of May 2020 none have been confirmed. More info: bit.ly/VegaSystem Credit: NASA/JPL-Caltech
Can you spot Vega? You may need to look straight up to find it, especially if observing after midnight.

The Night Sky Network program supports astronomy clubs across the USA dedicated to astronomy outreach. Visit nightsky.jpl.nasa.gov to find local clubs, events, and more!

NASA Space Place – Twinkle, Twinkle, Variable Star

Poster’s Note: One of the many under-appreciated aspects of NASA is the extent to which it publishes quality science content for children and Ph.D.’s alike. NASA Space Place has been providing general audience articles for quite some time that are freely available for download and republishing. Your tax dollars help promote science! The following article was provided for reprinting in September, 2014.

By Dr. Ethan Siegel

2013february2_spaceplaceAs bright and steady as they appear, the stars in our sky won’t shine forever. The steady brilliance of these sources of light is powered by a tumultuous interior, where nuclear processes fuse light elements and isotopes into heavier ones. Because the heavier nuclei up to iron (Fe), have a greater binding energies-per-nucleon, each reaction results in a slight reduction of the star’s mass, converting it into energy via Einstein’s famous equation relating changes in mass and energy output, E = mc2. Over timescales of tens of thousands of years, that energy migrates to the star’s photosphere, where it’s emitted out into the universe as starlight.

There’s only a finite amount of fuel in there, and when stars run out, the interior contracts and heats up, often enabling heavier elements to burn at even higher temperatures, and causing sun-like stars to grow into red giants. Even though the cores of both hydrogen-burning and helium-burning stars have consistent, steady energy outputs, our sun’s overall brightness varies by just ~0.1%, while red giants can have their brightness’s vary by factors of thousands or more over the course of a single year! In fact, the first periodic or pulsating variable star ever discovered—Mira (omicron Ceti)—behaves exactly in this way.

There are many types of variable stars, including Cepheids, RR Lyrae, cataclysmic variables and more, but it’s the Mira-type variables that give us a glimpse into our Sun’s likely future. In general, the cores of stars burn through their fuel in a very consistent fashion, but in the case of pulsating variable stars the outer layers of stellar atmospheres vary. Initially heating up and expanding, they overshoot equilibrium, reach a maximum size, cool, then often forming neutral molecules that behave as light-blocking dust, with the dust then falling back to the star, ionizing and starting the whole process over again. This temporarily neutral dust absorbs the visible light from the star and re-emits it, but as infrared radiation, which is invisible to our eyes. In the case of Mira (and many red giants), it’s Titanium Monoxide (TiO) that causes it to dim so severely, from a maximum magnitude of +2 or +3 (clearly visible to the naked eye) to a minimum of +9 or +10, requiring a telescope (and an experienced observer) to find!

Visible in the constellation of Cetus during the fall-and-winter from the Northern Hemisphere, Mira is presently at magnitude +7 and headed towards its minimum, but will reach its maximum brightness again in May of next year and every 332 days thereafter. Shockingly, Mira contains a huge, 13 light-year-long tail — visible only in the UV — that it leaves as it rockets through the interstellar medium at 130 km/sec! Look for it in your skies all winter long, and contribute your results to the AAVSO (American Association of Variable Star Observers) International Database to help study its long-term behavior!

Check out some cool images and simulated animations of Mira here: www.nasa.gov/mission_pages/galex/20070815/v.html

Kids can learn all about Mira at NASA’s Space Place: spaceplace.nasa.gov/mira/en/.

2014sept25_mira

Caption: NASA’s Galaxy Evolution Explorer (GALEX) spacecraft, of Mira and its tail in UV light (top); Margarita Karovska (Harvard-Smithsonian CfA) / NASA’s Hubble Space Telescope image of Mira, with the distortions revealing the presence of a binary companion (lower left); public domain image of Orion, the Pleiades and Mira (near maximum brightness) by Brocken Inaglory of Wikimedia Commons under CC-BY-SA-3.0 (lower right).

This article was provided by the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration.

About NASA Space Place

The goal of the NASA Space Place is “to inform, inspire, and involve children in the excitement of science, technology, and space exploration.” More information is available at their website: http://spaceplace.nasa.gov/

AAVSO Writer’s Bureau Digest For 22 April 2014

2013dec20_aavso_logoThe AAVSO Writer’s Bureau, hosted by the American Association of Variable Star Observers (www.aavso.org), is a selective aggregator of high-quality science content for the amateur astronomer. Several astronomy bloggers, science writers, and official astronomy publishers and organizations provide articles free-of-charge for redistribution through the AAVSO-WB. The five most recent Writer’s Bureau posts are presented below with direct links to the full articles on the author’s own website. CNYO thanks the authors and the AAVSO for making these articles available for free to all astronomy groups!

Starbirth in the Neighborhood

C.C. Petersen, The Spacewriter

2014april22__5_M83Galaxies are huge collections of stars, gas, dust, black holes, and planets. The Milky Way is a good example of a spiral galaxy. It also happens to have a bar of gas and dust and stars across its center, and many places where stars are being born. It turns that when astronomers look at other galaxies, particular spiral galaxies (and many colliding galaxies), they also see regions of starbirth.

Hubble Space Telescope has been astronomy’s “go to” machine in space when astronomers want to look at something like a distant galaxy. This Hubble image shows the pinwheel (spiral) galaxy M83, which lies in our southern hemisphere skies in the constellation Hydra. It’s about 15 million light-years away, and, as you can see here, is ablaze with starbirth regions spread across 50,000 light-years of space.

Read the full article at: thespacewriter.com/wp/2014/01/26/starbirth-in-the-neighborhood/

A Cosmic Bubble That’ll Soon Pop. Hard.

Phil Plait, slate.com

2014april22__4_jeffhusted_sharpless2_308Sometimes, I’m pretty happy our planet circles a relatively calm, normal star. Because when I look at stars like EZ Canis Majoris (aka WR 6, HR 2583, HD 50896, and other aliases), I think that things around here could be a lot less conducive for life.

Why? Because this:

Pretty, isn’t it? But the beauty belies a true monster.

This photo was taken by Jeff Husted, an astrophotographer who observers in the western US. It shows the star EZ CMa (for short), the star just left of center of that ethereal glowing bubble of gas. It’s what’s called a Wolf-Rayet star, one of the more terrifying beasts in the galaxy’s menagerie. It’s a star that started out life with more than 40 times the mass of the Sun, which made it super-hot and extraordinarily luminous. Stars like that can be hundreds of thousands of times as bright as the Sun! A planet orbiting it as close as the Earth to the Sun would be cooked to a vapor pretty rapidly.

Read the full article at: www.slate.com/blogs/…cosmic_bubble_from_a_galactic_monster.html

The Final Countdown Before a Supernova

Phil Plait, slate.com

2014april22__3_hst_sbw1I’m sometimes asked what I think the next exploding star in our galaxy will be. Most people expect I’ll say Betelgeuse, the red supergiant marking Orion’s right shoulder.

But Betelgeuse may not go supernova for another million years, which is a long, long time. There are several stars much closer to The End, and I recently learned of a new one: SBW1.

The star is a blue supergiant, a hot, energetic beast probably about 20 or so times the mass of the Sun. Stars like that don’t live long, just a few million years tops. But we know (we think) it’ll explode much sooner than that, because of that ring you see in the Hubble picture above. How does that ring tell us anything? Ah, glad you asked.

Read the full article at: www.slate.com/blogs/…/sbw1_a_star_on_the_verge_of_supernova.html

A Superluminous Supernova

CfA News, Harvard

2014april22__2_su201401Supernovae are the explosive deaths of massive stars. Among the most momentous events in the cosmos, they disburse into space all of the chemical elements that were produced inside their progenitor stars, including most of the elements essential for making planets and life. Astronomers have recognized for decades that there are several different kinds of supernovae, most fundamentally those that originate from a single massive star and those that develop when one member of a pair of binary stars becomes massive by feeding on its neighbor. Other factors like the stellar composition also come into account. Sorting out all these various complications is critical if astronomers want to be able to reliably classify any particular supernovae and thereby infer its intrinsic brightness, and then use its observed brightness as a measure of its distance.

Recent wide-field surveys searching for supernovae have found that the conventional schema for classifying supernovae may be even more complicated than previously thought. A few years ago a new class called superluminous supernovae was found, characterized by their emitting total radiated energies equal to about ten billion suns shining for a year. Some of these new objects were discovered at cosmological distances, helping to cement the notion that new types were being discovered, and further studies have found even more subdivisions, also based among other things on composition. These new superluminous supernovae can be identified and characterized by the particular way their light fades away after the brightness peak, driven in part by the radioactive decay of elements manufactured in the explosions.

Read the full article at: www.cfa.harvard.edu/news/su201401

New Cutoff For Star Sizes

John Bochanski, Sky & Telescope

2014april22__1_Brown_DwarfAstronomers have found a gap between “real” and “failed” stars.

What does the smallest star look like? This question is deceptively difficult to answer. Stars spend most of their lives fusing hydrogen in their cores, a prime time of life called the “main sequence.” As you go down the scale of stellar sizes on this sequence, stars become dimmer, cooler, and less massive. But determining the absolute properties of the smallest stars — their mass, radius, temperature, and overall light output — is challenging for at least three big reasons.

Read the full article at: www.skyandtelescope.com/astronomy-news/new-cutoff-for-star-sizes/