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Category Archives: Astronomy

astronomy | Definition & Facts | Britannica

Posted: March 31, 2020 at 6:54 am

Astronomy, science that encompasses the study of all extraterrestrial objects and phenomena. Until the invention of the telescope and the discovery of the laws of motion and gravity in the 17th century, astronomy was primarily concerned with noting and predicting the positions of the Sun, Moon, and planets, originally for calendrical and astrological purposes and later for navigational uses and scientific interest. The catalog of objects now studied is much broader and includes, in order of increasing distance, the solar system, the stars that make up the Milky Way Galaxy, and other, more distant galaxies. With the advent of scientific space probes, Earth also has come to be studied as one of the planets, though its more-detailed investigation remains the domain of the Earth sciences.

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Astronomy is the study of objects and phenomena beyond Earth. Astronomers study objects as close as the Moon and the rest of the solar system through the stars of the Milky Way Galaxy and out to distant galaxies billions of light-years away.

Since the late 19th century, astronomy has expanded to include astrophysics, the application of physical and chemical knowledge to an understanding of the nature of celestial objects and the physical processes that control their formation, evolution, and emission of radiation. In addition, the gases and dust particles around and between the stars have become the subjects of much research. Study of the nuclear reactions that provide the energy radiated by stars has shown how the diversity of atoms found in nature can be derived from a universe that, following the first few minutes of its existence, consisted only of hydrogen, helium, and a trace of lithium. Concerned with phenomena on the largest scale is cosmology, the study of the evolution of the universe. Astrophysics has transformed cosmology from a purely speculative activity to a modern science capable of predictions that can be tested.

Its great advances notwithstanding, astronomy is still subject to a major constraint: it is inherently an observational rather than an experimental science. Almost all measurements must be performed at great distances from the objects of interest, with no control over such quantities as their temperature, pressure, or chemical composition. There are a few exceptions to this limitationnamely, meteorites (most of which are from the asteroid belt, though some are from the Moon or Mars), rock and soil samples brought back from the Moon, samples of comet and asteroid dust returned by robotic spacecraft, and interplanetary dust particles collected in or above the stratosphere. These can be examined with laboratory techniques to provide information that cannot be obtained in any other way. In the future, space missions may return surface materials from Mars, or other objects, but much of astronomy appears otherwise confined to Earth-based observations augmented by observations from orbiting satellites and long-range space probes and supplemented by theory.

A central undertaking in astronomy is the determination of distances. Without a knowledge of astronomical distances, the size of an observed object in space would remain nothing more than an angular diameter and the brightness of a star could not be converted into its true radiated power, or luminosity. Astronomical distance measurement began with a knowledge of Earths diameter, which provided a base for triangulation. Within the inner solar system, some distances can now be better determined through the timing of radar reflections or, in the case of the Moon, through laser ranging. For the outer planets, triangulation is still used. Beyond the solar system, distances to the closest stars are determined through triangulation, in which the diameter of Earths orbit serves as the baseline and shifts in stellar parallax are the measured quantities. Stellar distances are commonly expressed by astronomers in parsecs (pc), kiloparsecs, or megaparsecs. (1 pc = 3.086 1018 cm, or about 3.26 light-years [1.92 1013 miles].) Distances can be measured out to around a kiloparsec by trigonometric parallax (see star: Determining stellar distances). The accuracy of measurements made from Earths surface is limited by atmospheric effects, but measurements made from the Hipparcos satellite in the 1990s extended the scale to stars as far as 650 parsecs, with an accuracy of about a thousandth of an arc second. The Gaia satellite is expected to measure stars as far away as 10 kiloparsecs to an accuracy of 20 percent. Less-direct measurements must be used for more-distant stars and for galaxies.

Two general methods for determining galactic distances are described here. In the first, a clearly identifiable type of star is used as a reference standard because its luminosity has been well determined. This requires observation of such stars that are close enough to Earth that their distances and luminosities have been reliably measured. Such a star is termed a standard candle. Examples are Cepheid variables, whose brightness varies periodically in well-documented ways, and certain types of supernova explosions that have enormous brilliance and can thus be seen out to very great distances. Once the luminosities of such nearer standard candles have been calibrated, the distance to a farther standard candle can be calculated from its calibrated luminosity and its actual measured intensity. (The measured intensity [I] is related to the luminosity [L] and distance [d] by the formula I = L/4d2.) A standard candle can be identified by means of its spectrum or the pattern of regular variations in brightness. (Corrections may have to be made for the absorption of starlight by interstellar gas and dust over great distances.) This method forms the basis of measurements of distances to the closest galaxies.

The second method for galactic distance measurements makes use of the observation that the distances to galaxies generally correlate with the speeds with which those galaxies are receding from Earth (as determined from the Doppler shift in the wavelengths of their emitted light). This correlation is expressed in the Hubble law: velocity = H distance, in which H denotes Hubbles constant, which must be determined from observations of the rate at which the galaxies are receding. There is widespread agreement that H lies between 67 and 73 kilometres per second per megaparsec (km/sec/Mpc). H has been used to determine distances to remote galaxies in which standard candles have not been found. (For additional discussion of the recession of galaxies, the Hubble law, and galactic distance determination, see physical science: Astronomy.)

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Astronomy for Beginners | Night Sky Facts, FAQs …

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Ali Matinfar captured this image of stargazers under the Milky Way from the Mesr Desert in Iran. Ali Matinfar / Online Photo Gallery

Did the astronomy bug bite you while you were out last night? Feeling inspired to learn about the wonders of the sky, the solar system, and all the science behind them? Let this page serve as your guide to astronomy for beginners.

Check out what's up in the night sky this week. Get advice for buying your first telescope. And find the best coverage youll find online of upcoming celestial events such as eclipses and meteor showers.

The best guide to astronomy for beginners is the night sky. All you really need to do to get started is look up preferably at night! You'll find an amazing treasure chest of astronomical wonders, even if you don't have a telescope.

Our most popular (and free) offering, "This Week's Sky at a Glance," guides you to the naked-eye sky, highlighting the major constellations and planets viewable in the evening sky, with occasional dips into deep-sky territory. (Download the free app for iTunes or Android.)

If you'd rather listen while under the stars, download our monthly astronomy podcast and take it with you when you venture out tonight for a guided tour to the night sky.

Or do your own sleuthing with our interactive sky chart.

If there are any major celestial events, such as comets, eclipses, or meteor showers, you'll find all the latest information (including instructions on where to look and detailed sky charts) in our observing news section.

Even though you don't need to know the Greek names of the constellations or understand the nature of black holes in order to relish the night sky, you might want to anyway. We provide a rich supply of information and resources on astronomy for beginners.

You'll also find a growing supply of answers to frequently-asked astronomy questions, be they related to the hobby or science of astronomy.

The naked-eye sky is full of astronomical treasures, and it gets even better with a little magnification. But don't feel you have to go out and buy a high-power telescope right away. Often the best first telescope is a pair of binoculars. Binoculars can give you the wide-field view that's essential to really learning your way around the night sky. Find out more about choosing and using binoculars here.

Once you're ready for a telescope, we have more than a few words of advice! You'll want to check out two digestible articles on the topic of choosing your first telescope: "What to Know Before Buying a Telescope" and "How to Choose a Telescope." You might also be interested in our video guides to choosing, using, and equipping your telescope.

Once you're ready to take on deep-sky challenges, such as spotting faint galaxies and fuzzy nebulae, prepare for a dive into deep celestial seas with Sky & Telescope's Deep-Sky Observing Collection.

And if you're looking to get started in astrophotography, be sure to check out our free Astrophotography Primer. Enter your email to download the ebook for free, plus receive our weekly e-newsletter with the latest astronomy news.

Astronomy can be an enlightening solitary activity, but it can also be fun to have company and advice from seasoned experts. Discover astronomy clubs and other organizations near you or find local astronomy-related events in our events calendar. (Or if you're already involved, submit your own club or event.)

Also, keep up with the Sky & Telescope community online at Facebook, Twitter, or Instagram.

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Unlike Earth, Mars may have never had a global magma ocean – Astronomy Magazine

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At least once in its past, Earth existed as a roiling ball of molten rock that might have had the consistency of room-temperature oil, but would been untouchable at some 2,000 degrees Fahrenheit (1,090 degrees Celsius).

As magma oceans ebbed and flowed, the tumult might have launched elements conducive for life out of the rock and into our atmosphere. Researchers previously thought that maybe similar fluid dynamics and the resulting spewing of life-supporting materials likewise happened on Mars. But new research suggests that's not the case.

Weve had so little time to think about how a planet would evolve without a melting step, its hard to tell if this is a net positive or net negative for [the possibility of] life, says Francis McCubbin, a NASA national materials coordinator and researcher who co-authored the new research.

By studying meteorites that came from Mars, McCubbin and his colleagues determined that the planet hosts two regions where the rock contains different ratios of hydrogen varieties. If the planet had once been awash in liquid rock, the same ratio of hydrogen types would be found all over the place, the team concluded in their Nature Geoscience paper.

Hydrogen analysis is one way to figure out whether Mars ever had a global magma ocean, McCubbin says. Other, yet-unstudied chemical systems on the planet could reveal ocean formation. Thatspart of why McCubbin says its too early to consider this finding a thumbs-down for the possibility of life on Mars and why their team plans to keep looking for signs of a once-liquid planet.

Before our solar system had planets, it had dust and gas. When those particles started clumping together, researchers think the clumps collided again and again until entire planets formed. Eventually, the clusters melted into an ocean of magma. Like a blender mixing strawberries and bananas into a smoothie, liquifying would swirl all the deposits from the early solar system together. The process would also churn material from inside the planet core and release it into the atmosphere, McCubbin says, including elements and chemicals necessary for life.

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Unlike Earth, Mars may have never had a global magma ocean - Astronomy Magazine

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Necroplanetology: The Strangest Field of Astronomy You’ve Never Heard Of – ScienceAlert

Posted: at 6:54 am

In 2015, astronomers found something weird. It was a white dwarf star, 570 light-years from Earth, with a peculiar dimming pattern. It dimmed several times to varying depths, each depth repeating on a 4.5 to 5-hour timeframe; and its atmosphere was polluted with elements usually found in rocky exoplanets.

It didn't take long before they figured it out. The gravity of the dead star was in the process of shredding and devouring bodies in orbit around it, a violent process known rather politely as tidal disruption.

The star is called WD 1145+017, and it's now being used as a proof of concept for a new field of planet study, forensic reconstruction of planetary bodies to understand what they were like, and how they died.

Astronomers from the US and the UK are calling this field necroplanetology.

Their analysis of WD 1145+017 has been accepted into The Astrophysical Journal, and is available on arXiv. And it could, the researchers say, be applied to future discoveries similar to the white dwarf system to piece together how planets die orbiting different kinds of dead stars.

Although white dwarfs eject a lot of material when they die in a series of violent thermonuclear explosions, planets can somehow survive the process. Not only have we found planets in orbit around white dwarf stars, we have found elements in the atmospheres of white dwarf stars that are usually found inside rocky exoplanets.

The surface gravity of white dwarfs is so intense that these heavier elements would sink quite quickly, indicating that the star must have accreted the material quite recently, from a body that survived the star's death throes.

To try and determine how WD 1145+017 got the way it did, astronomers from the University of Colorado, Boulder, Wesleyan University, and the University of Warwick in the UK conducted a series of simulations to place constraints on the tidally disrupted body.

They tweaked structural components of an orbiting body, such as the size of the core and mantle; the composition of the mantle, rocky or icy; and the presence of a crust. This resulted in 36 different simulated bodies.

Then, they set each of these 36 bodies orbiting a star like WD 1145+017, around 60 percent of the mass of the Sun, and 2 percent of its size (white dwarfs are pretty dense).

This orbit was 4.5 hours, as per the material orbiting WD 1145+017, and each simulation ran for 100 orbits. And finally, the resulting light curves for the tidal disruption of each body were then compared with the real-life light curve of WD 1145+017.

These simulations showed that the bodies most likely to produce what we observe in WD 1145+017 have a small core, and a low-density mantle, "resembling an asteroid with a partially differentiated structure and volatile-rich mantle like Vesta," the researchers wrote in their paper.

The bodies are relatively low mass, and have bulk density high enough to maintain structure for a while, but low enough that their mantles are disrupted. These attributes are consistent with the lack of small particles found in other observations of the star, since these would sublimate quickly.

And, in fact, they offer some clues as to other mysterious stars as well - such as the famous KIC 8462852, AKA Tabby's star, whose inconsistent dimming is a source of much puzzlement among astronomers.

KIC 8462852, since its strange behaviour was first discovered, has turned out not to be the only star exhibiting such strange dimming. A survey last year turned up another 21 strangely dimming stars that could have similar dynamics.

And other white dwarfs slurping down orbiting bodies have been discovered, too. ZTF J0139+5245 and WD J0914+1914 were both discovered tidally disrupting planets last year.

These stars could be simulated using the team's new methods, too.

"These are the first members of a larger class of dying planetary systems that must be studied by pairing spectroscopic and photometric observations with disruption simulations, either tidal as in WD 1145+017 or rotational as Veras et al. (2020) proposes for the body transiting ZTF J0139+5245," the researchers wrote in their paper.

"This multi-pronged approach would use the death of these planetary systems in action to study fundamental properties of exoplanetary bodies that are otherwise inaccessible: a study in necroplanetology."

The research has been accepted into The Astrophysical Journal, and is available on arXiv.

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How to explore the universe while you’re stuck at home – Astronomy Magazine

Posted: at 6:54 am

3. The Hubble Space Telescopes homepage

The most famous space telescope in history a joint mission undertaken by NASA and the ESA has its own website with loads of information on exoplanets, nebulae, stars, galaxies, and much more. You can sift through collections of thousands of photos, countless videos, and informative articles. offers a lot of knowledge in one place. Whether youre looking for quick facts on the telescope, its mission, or its science, or just the latest Hubble news, the telescope's online portal has you covered. The site also has educational resources to help making teaching the next generation about Hubbles mission and astronomy as a science both easy and fun!

4. Cosmos: Possible Worlds

In 1980, Carl Sagan mesmerized the world when he hosted a humbling, captivating, and, most of all, accessible television series called Cosmos: A Personal Voyage. This show written by Sagan, Steven Soter, and Emmy and Peabody Award-winner Ann Druyan (who married Sagan in 1981) thoughtfully explored the wonders of the universe, as well as our place in it. (By the way, if you havent heard Sagans famous Pale Blue Dot monologue, do yourself a favor and take a few minutes to listen to it.)

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How to explore the universe while you're stuck at home - Astronomy Magazine

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Discover the secrets of the Northern Pinwheel Galaxy – Astronomy Magazine

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The western spiral armIf you have at least a 12-inch scope, trace the western arm outward from where it abruptly turns south; about 3.3' southwest of the galaxys nucleus, youll find a small bright area hugging the edge of the narrow dark lane. This is NGC 5453. Continue to follow the western arm south and youll find a triangle of stars framing the area where it fans out and vanishes. Again, Ive seen more than one sketch depicting all three points of this triangle as foreground stars, but the southernmost point is not a star careful examination shows it has soft edges. This is the nebula NGC 5455. This HII region is where the type II supernova 1970G appeared in July 1970, reaching magnitude 11.5. The remnant of this supernova has since been observed by Chandra as a bright, compact X-ray source. Brighter than NGC 5453, NGC 5455 can be seen with an 8-inch scope.

Type II supernovae explosions of single, massive stars are strongly associated with HII regions of galaxies, where such stars are born. By contrast, type Ia supernovae, which occur when a white dwarf in a binary system gravitationally siphons enough gas off its companion to explode, are not necessarily associated with HII regions. On August 24, 2011, the type Ia supernova 2011fe (originally designated PTF11kly because it was detected by the Palomar Transient Factory) appeared within this spiral arm of M101 and was visible in amateur scopes. You can see SN2011fe as a bright blue star within the western spiral arm in the image of M101 I took after it was discovered (page 53). But in a matching close-up from the images taken last year for this article, SN2011fe had vanished into obscurity.

This type Ia supernova appeared in a faint portion of this spiral arm, rather than within one of M101s numerous HII regions. Type Ia supernovae explode when a white dwarf reaches 1.4 solar masses, and thus are equal in brightness. Therefore, they serve as standard candles for calculating cosmic distances; SN2011fe helped refine our estimate of the distance to M101.

A few more treasures hide in the far western arm. Trace the arm outward from the core until you reach the bright, southward-pointing spearhead shape at the tip. A magnitude 14 foreground star marks its northwest edge. This bright shape is produced by the combined light of two adjacent nebulae: NGC 5450 in the southern half and NGC 5447 in the northern. Larger apertures may allow you to see the narrow dark gap between them.

If you have a large scope, you can try to spot M101s two most difficult targets. Check the far western arm at a point just south of a line between the southern star in the right triangle and the galaxys nucleus. If you see a subtle brightening there, youve found NGC 5449. Next, check the point two-thirds of the way along a line between the southern star in the right triangle and the turning-point star where the western arm abruptly turns south. A tiny bright spot there might be NGC 5451. However, be advised that a faint close double star in the Milky Way may fool you into thinking youve seen NGC 5451 when you havent.

I hope you will enjoy the thrill of hunting for these challenging NGC objects within M101. Your patience will be rewarded with the still-greater thrill of finding nebulae within a distant galaxy. Then, the next time someone mentions The Pinwheel Galaxy, you can both impress and surprise them by saying Oh, yes, the Pinwheel, in Ursa Major!

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The Sun: Extremely loud and incredibly hot – Astronomy Magazine

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You know, for how often we see the Sun, theres an awful lot we dont know about it.

I mean, we know its powered by nuclear fusion, that its 92.96 million miles away, and that its about a million times bigger than the Earth by volume.But theres more to it than that. Like, why is its corona so hot? How does the Sun make solar wind? How does it give Superman his powers?

Luckily, NASA is hard at work answering some of these questions.

In August 2018, NASA launched a mission to touch the Sun. Its called the Parker Solar Probe, and its designed to withstand super-high temperatures. Over the next few years, itll swoop around the Sun several more times, getting closer than any spacecraft before it.

And it will actually fly through the Suns corona, which is the wispy outer layer thats visible during a solar eclipse. Thats nuts because the corona is incredibly hot millions of degrees Fahrenheit. Turns out the surface of the Sun is only a few thousand degrees.

The probe will also take measurements of the hot, electrically charged plasma that comes off of the Suns corona and streams through space, called solar wind. These winds are what cause auroras on Earth and on other planets, too.

One of the biggest things researchers hope to learn is how the Sun transports energy into the corona in the first place. How is it so hot? And how does it push the solar wind out at such high speeds? Scientists have suspected that magnetic fields have something to do with it, but they dont know exactly what.

The probe has already made a few laps around the Sun and reported back. So far, Parkers found out that there are dramatic changes in the vibrations of the magnetic fields coming from the Sun, which seem to get weaker as they get farther away. Though the findings arent yet conclusive, its possible that these magnetic interactions are whats heating the Suns corona and accelerating the solar wind.

The other super rad thing weve gotten from the Parker Solar Probe are some sound clips. Lets listen.

What were hearing is the solar wind. Thats the whooshing and whistling noises.

Now, this isnt literally sound, like we think of it on Earth. Theres no microphone on board the solar probe. Instead, its measuring the frequencies and amplitudes of the pressure waves in the solar wind.

And that is kind of like sound because here on Earth, we hear pressure waves as sound. So all the researchers had to do was translate the waves that the probe measured into the types of waves we can hear.

I dont know, Im counting it.

So different sounds are produced by different types of particles doing different things, like, if a beam of electrons streams along a magnetic field.

Or, if electrons spin around a magnetic field.

So, anyway, the researchers werent just looking for some sweet new space sound effects. Theyre going to look into these data some more and see if they can learn about how the hot corona and the solar wind work.

Scientists are stoked about these initial results. Theyre really hopeful that more data from the Parker Solar Probe will spill some of the Suns remaining secrets.

By the way the Sun does make actual sound. We just cant hear it because space is a vacuum, so the sound waves dont have a way of getting to us. But if we could hear the constant roar, itd be pretty loud, even from here. One heliophysicist crunched the numbers and estimates the noise would be around 110 decibels, or about the same volume as speakers at a rock concert.

Im suddenly really glad space is a vacuum.

Anyway, the Parker probe isnt the only way were getting new info about the Sun.

Just a few days ago, the European Space Agency and NASA successfully launched a joint Solar Orbiter a new mission on its way to go check out the Sun.

And lets not forget the good ol fashioned telescope.

In fact, the new Daniel K. Inouye Solar Telescope in Hawaii the biggest solar telescope on Earth has taken its first video footage of the Sun. These new shots are the highest-resolution views of our star yet, showing details on the Suns surface as small as 18 miles across.

On the Sun, hot plasma rises to the surface, cools and sinks back down in a process called convection, like water boiling in a pot. The grainy pattern you see are these cells of plasma, which turn over about every five minutes.

The brightest spots are the hottest, where new plasma has just risen up from below. And the darker spots are where cooler plasma is sinking down. These plasma cells are roughly the size of Texas.

The bubbling motions are important for researchers to study because plasma is electrically charged, so its motions can create magnetic fields. And its the Suns magnetic fields that are responsible for some of its most dynamic behavior, like solar storms, which can mess with satellites and power grids on Earth.

The new telescope can also do more than take pretty pictures. Its got all sorts of instruments that can measure information about the magnetic forces in the Suns atmosphere.

With all this new information, scientists are closer than ever to figuring out how, exactly, our Sun keeps on shining.

Anna Funkis associate editor for Astronomy's sister magazine, Discover. Follow her on Twitter @DrAnnaFunk and check out ourYouTube channel for more videos.

This video is based on reporting by Erika K. Carlson and Nathaniel Scharping.

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The Sun: Extremely loud and incredibly hot - Astronomy Magazine

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Hubble anniversary events impacted by COVID-19 pandemic – Astronomy Now Online

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The Hubble Space Telescope as it was last seen in 2009 during a fifth and final space shuttle servicing mission. The iconic observatory will mark its 30th year in space on 24 April. Image: NASA

As reports continue about the spread of COVID-19 (coronavirus), this Announcement details the updates for the planned Hubble 30th Anniversary Image Unveiling events.

The health and safety of visitors and organisers of Hubble 30 celebrations events remain our top priority. The original plan was to have unveiling events taking place on or shortly after the anniversary date of 24 April. ESA/Hubble is now shifting its vision to instead hold events in the coming months that are a general celebration of the Hubble Space Telescopes splendid 30 years.

We understand the spread of the coronavirus may impact the feasibility of hosting public events, particularly those with large audiences. We are therefore flexible with regard to the new dates for the Hubble Space Telescopes 30th anniversary image to be featured at various European facilities. The showcasing of the image may form part of a general Hubble celebration event any time after the 24 April public image release, and before 30 September 2020.

Instead of only display events, ESA/Hubble is encouraging a broad style of events and activities that celebrate Hubble in general, and its 30 years of scientific discoveries. As events become more widespread throughout the year, ESA/Hubble will also support activities in whatever way possible, including the provision of additional materials and possible on-site support, such as qualified representatives from ESA/Hubble who can speak at various events.

Public health should remain paramount in this situation and ESA/Hubble is confident that the presence of the Hubble 30th anniversary image at various European locations will continue to be a source of amazement to public guests. Updates will be provided at a later date regarding the new event dates and plans, and general Hubble 30 updates will be posted on this page.

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Mobile astronomy: Put the Milky Way in your pocket with ‘Our Galaxy’ smartphone app –

Posted: March 26, 2020 at 5:53 am

From time to time at star parties, I encountered someone who isn't very impressed with the dim, fuzzy object I'm showing them through my telescope. But once I explain what the object is, how far away it is, and how it connects to our place in the galaxy and the wider universe beyond, it sparks their imagination and they look at it again with renewed interest and appreciation. A new fun and educational app called Our Galaxy will let anyone learn about our place in the cosmos, and feel that sense of wonder.

In addition to the obvious bright planets and stars, the night sky is sprinkled with star clusters, nebulas, and distant galaxies, many of which are revealed by looking through binoculars and backyard telescopes. Astronomers refer to those exotic objects as deep-sky objects. Their positions in the sky aren't completely random. Star clusters and nebulas populate the spiral arms of our home galaxy, the Milky Way with more of them occurring closer to the center of the galaxy and fewer of them appearing along its outer rim. Their locations in the sky allow astronomers to trace out the structure and dimensions of our galaxy, and to determine where new stars are being formed within it.

Related: Stunning photos of our Milky Way Galaxy (gallery)

Planetary nebulas are the corpses of stars not unlike our sun that reached the end of their lives. Those objects can appear anywhere in our sky because our sun sits within a 3-dimensional volume of space; surrounded by stars of all ages. Globular clusters are spherical, densely-packed collections of old stars that orbit our galaxy like bees around a hive so they tend to be found near the band of the Milky Way, but not inside it. Distant galaxies are sprinkled throughout the sky, but they can only be mapped and observed where our own galaxy's gas and dust don't block their distant light.

Bill Tschumy, one of the creators of the popular SkySafari app, has created the perfect tool to understand our place in the Universe. The Our Galaxy app for iOS and MacOS lets users visualize the locations and physical properties of deep-sky objects within and around our galaxy. The app is a relatively small download at less than 60 Mb. Once loaded on your iPhone, it puts a deep sky expert in your pocket and the larger display on an iPad really shows off its wealth of detailed imagery.

The Our Galaxy app can be operated in two modes that are enabled by tapping Galaxy or Sky on the app's toolbar. The toolbar also features icons to open the search menu and Views library, read a page of information about the selected object, toggle red-light night mode, open the app's settings menu and help. Two whimsical spaceship-shaped icons in the toolbar serve as zoom controls one flies you closer, the other flies you out.

Galaxy View presents a 3-dimensional model of our Milky Way's barred spiral form that you can tilt and rotate, and zoom in and out of. A single tap in the Settings Orientation menu lets you select preset orientations, such as an edge-on view and a face-on view. In the Center menu, you can choose to keep our sun in the center, or rotate around the galactic core or around a selected star or deep-sky object. Across the top of the screen are shown your distance from the selected object, and the field of view (FOV) being displayed in light-years.

Sky View draws a rectangular (orthographic) map of the entire sky as viewed from Earth. Sky coordinates in degrees are labelled around the perimeter of the map. The major stars and lines that form the constellations are plotted in white on a black background. The deep-sky objects are overlain using colored symbols. The map can be enlarged and panned around. Tapping a symbol shows its object's name. Plotting one or more categories of deep-sky objects on the map view illustrate how they can be used to define our galaxy's structure, or be completely independent of it all useful information for understanding how galaxies like ours are structured. A single tap switches between sky and galaxy view.

The app is highly configurable. You can decide whether to display labelled names next to the symbols, identify the various spiral arms of the galaxy, and show the Constellation Sectors the portions of the Milky Way that lie in the direction of certain constellations, such as Orion, Gemini or Cygnus.

To clean up the view, simply enter the settings menu and tap the remove options.

The app contains an extensive library of stars and objects. An object can be selected by typing its name or its designation into the search menu or by tapping its symbol on the screen. Multiple deep-sky objects can be displayed at the same time, as I describe below.

The app's powerful search menu allows you to type all or a portion of an object's name or designation, include or exclude object types, and limit the search to specific ranges of magnitude (brightness), distance, age, size and more. You can even search all constellations, or select a single constellation.

The list of results can then be displayed on the map or 3D model. It's especially interesting to see how the stars and deep-sky objects of a single constellation fall at vastly different distances from our sun.

The more you work with the app, the more you will learn about astronomy, astrophysics, and cosmology all presented using clear, understandable text and graphics.

The Views library is especially educational for understanding how various classes of objects populate the galaxy. Nine categories are offered: individual stars and OB Associations (hot, bright stars), open and globular clusters, various types of nebulas, galaxies, and our galaxy's structural components. There is also an entry for the list of well-known Messier objects. Each entry has an information icon to summon a description of that object class.

Tapping any category opens a sublist that allows you to select all members of the class, or sub-groups. For example, in the Diffuse Nebulae view, you can treat emission and reflection nebulas as separate groups, or combined, each type color-coded appropriately (with red for light emitted from hydrogen, blue for starlight scattered off dust, and green for both phenomena).

The Visibility menu contains sliders to plot galactic axes and to add wire mesh representations of the galaxy's central bulge, dark matter halo sphere, and more.

For cosmology buffs, the app contains 3D locations for hundreds of galaxies. Selecting the galaxy category and using "Galaxy view" puts you 92 billion light-years away from home. Manipulating the model shows how some galaxies concentrate in groups while others leave empty voids in the visible universe.

The Our Galaxy app will give you a true perspective on our place in space. Bill Tschumy has posted a YouTube video demonstration of the app here. Enjoy exploring the galaxy and, as always, keep looking up!

Chris Vaughan is an astronomy public outreach and education specialist at AstroGeo, a member of the Royal Astronomical Society of Canada, and an operator of the historic 74-inch (1.88-meter) David Dunlap Observatory telescope. You can reach him via email, and follow him on Twitter @astrogeoguy, as well as on Facebook and Tumblr. Follow SkySafari on Twitter @SkySafariAstro. Follow us on Twitter @Spacedotcom and on Facebook.

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The true impact of SpaceXs Starlink constellation on astronomy is coming into focus – The Verge

Posted: at 5:53 am

Ever since SpaceX launched its first batch of internet-beaming satellites last year, astronomers have watched with dread as the company continued to blast more spacecraft into orbit. Could this ballooning constellation of bright satellites fill the night sky with artificial light and muck up observations of the Universe for years to come? Now, new data is partially validating what many astronomers have feared since that first launch.

Up until now, people have been somewhat in the dark about the true impact of SpaceXs internet-from-space project called Starlink, which envisions nearly 12,000 of these satellites orbiting Earth. SpaceXs satellites are super bright compared to others, and astronomers have been worried that with so many luminous satellites in the sky, the odds of one passing in front of a telescope and obscuring an image will increase.

It turns out, some astronomers have reason to be concerned. Certain types of astronomy may be more negatively affected than others, one peer-reviewed study shows, particularly those kinds that scour large swaths of the sky over long periods of time looking for faint, faraway objects. That means scientists looking for distant objects beyond Neptune including the hunt for the mysterious Planet Nine might have trouble when Starlink is complete. Additionally, Starlink may be much more visible during twilight hours, or the first few hours of the night, which could be a major problem in the hunt for massive asteroids headed toward Earth. It depends on what science youre doing, and thats really what it comes down to, Jonathan McDowell, an astrophysicist at Harvard and spaceflight expert who wrote the study accepted by Astrophysical Journal Letters, tells The Verge.

Meanwhile, scientists are also learning if SpaceXs effort to mitigate the brightness of its satellites is actually going to work. The company coated one of its satellites in an attempt to make it appear less visible in the sky. Now, the first observations of that satellite are being published, and the coating is working but it might not be enough to make everyone happy. It doesnt solve the issue, Jeremy Tregloan-Reed, a researcher at the University of Antofagasta and lead author on the study, which is undergoing peer review at Astronomy and Astrophysics Letters, tells The Verge. But it shows that SpaceX has taken on board astronomers concerns, and it does appear to be trying to solve the situation.

For astronomers, light is everything. Observing celestial objects in different wavelengths of light is the best method we have for exploring the Universe. Thats why adding artificial light to the sky freaks out so many scientists. Some astronomers take long-exposure images of the sky, gathering as much light as possible from distant objects and when a bright satellite reflecting light from the Sun passes overhead, it can leave a long white streak that ruins the picture.

Of course, the sky is a big canvas, and one tiny satellite isnt going to be a major headache. A host of factors dictate exactly how and when satellites will be a problem. A satellites size, shape, height, and path around Earth all affect exactly how much light it reflects from the Sun and where people will see it the most. Meanwhile, the time of year and the time of night determine how much sunlight is shining on a satellite at any given moment.

To figure out Starlinks exact impression on the night, McDowell made a comprehensive simulation based on what we know about where all of the Starlink satellites are going. Ahead of launching its constellation, SpaceX had to file multiple requests with the Federal Communications Commission, detailing where the company planned to send all of its spacecraft. Using that information, McDowell came up with a snapshot of which areas will see the most satellites overhead and what times of night will be the worst for observations.

In the more northern and southern latitudes, Starlink satellites will dominate the horizon during the first and last few hours of the night. In the summertime, itll be much worse, with hundreds of satellites visible for those in rural areas away from city light pollution. Where I live in [Boston], I can see the planes hovering over Logan [Airport] on the horizon, says McDowell. Thats what it will look like, but itll be satellites and itll be a lot of them. SpaceX declined to comment for this story.

While people living in cities and towns wont really notice, this spells bad news for those hunting really distant faint objects using long exposures. The longer that you have the shutter open for, the more that youre likely to have an observation impeded by one of these streaks that are quite bright, Michele Bannister, a planetary astronomer at the University of Canterbury in New Zealand who helped McDowell with his research, tells The Verge. That means those hunting Planet Nine and objects at the edge of the Solar System have some cause for alarm.

Additionally, asteroid hunters are going to be extra affected by this constellation, says McDowell. Theyre really hosed, because they need to look at twilight, he says. Scientists looking for asteroids orbiting near Earth often look for these objects near the Sun; they observe just after sunset when they can see the part of the sky near the Sun thats too bright to see during the day. Thats where the problem with illuminated Starlink satellites is the worst, he says. Even from regular 30-degree latitude observatories, theyre going to have serious problems.

As for what that means for these astronomy fields, one obvious concern is that a potentially hazardous asteroid could go unnoticed until its too late to act appropriately. Its also possible observers will have to take expensive countermeasures to get the kinds of images they want. It may mean you have to observe twice as long, if you have to throw away half your data, says McDowell. So thats expensive. Or you may need to make changes to your telescope design, to stop reflections from a satellite.

The silver lining here, at least, is that McDowells study found that Starlink may not really have a big effect on a lot of other astronomers work, especially those who only look at small slices of the night sky for certain periods of time. But his work does fly in the face of what SpaceX CEO Elon Musk has said about Starlink and its astronomy repercussions. I am confident that we will not cause any impact whatsoever in astronomical discoveries. Zero, Musk said during a space conference at the beginning of March. Thats my prediction. And well take corrective action if its above zero.

Despite Musks brazen proclamation, the truth is SpaceX has already taken some corrective action, but new research shows it may not be enough to silence all of the companys critics.

On its third Starlink launch in January, SpaceX included a satellite that had been painted with an experimental coating, meant to darken the spacecrafts reflectivity. Nicknamed DarkSat, the spacecraft has been of particular interest to amateur satellite trackers. Various observatories have taken images of DarkSat as its passed overhead to gauge just how much fainter it appears compared to its cohort.

The answer, it seems, is that DarkSat is indeed darker but only slightly. Once it reached its final orbit, the satellite appeared 55 percent fainter compared to another bright Starlink satellite, according to Tregloan-Reeds study. Thats based on the initial observations he made using a telescope at the Ckoirama Observatory in Chile. The DarkSat coating does push the satellite beyond being able to be seen with the naked eye, says Tregloan-Reed.

Thats a big reduction, but 55 percent may not be enough for some observatories. The Vera Rubin Observatory in Chile is still under construction, but it has the massive task of surveying the entire night sky. Its going to be able to give us the history of the Solar system in absolutely intricate and amazing detail, says Bannister of the survey. And I think thats definitely something that is under threat. People at the observatory have estimated that the Starlink satellites would need to be even fainter than DarkSat in order to truly stay out of the way and not saturate the images gathered.

The good news is that SpaceX has hinted that more extreme countermeasures may be on their way. During its latest launch, a SpaceX employee noted that while the coated satellite showed a notable reduction in brightness, a future Starlink satellite may be equipped with a sunshade to further reduce reflectivity. We have a couple other ideas that we think could reduce the reflectivity even further, the most promising being a sunshade that would operate in the same way as a patio umbrella, or a sun visor but for the satellite, Jessica Anderson, a lead manufacturing engineer at SpaceX, said during the live stream.

Tregloan-Reed says hes hopeful about some kind of shade. If that was to work then in theory it would block out the sunlight completely, he says.

Still, that doesnt solve every single astronomy problem because even a darkened satellite can still be a nuisance. Astronomers searching for planets beyond our Solar System, for instance, often take very sensitive measurements of distant stars, looking for dips in their brightness that might indicate a foreign planet passing by. If a satellite, even a dark one, were to pass in front of a star someone was observing, it could throw off the search for these alien worlds.

No matter what, it seems that a giant constellation is going to have some kind of negative impact on someone it cant be helped. And looking at the big picture, SpaceX isnt alone in its attempt to create a mega-constellation of satellites. The company just gets the most attention because its proposing the largest number of spacecraft, and its vehicles are big, bright, and lower in the sky compared to other proposed constellations. Others like OneWeb and Amazon want to also fill the sky with internet-beaming vehicles.

Such a large influx of artificial bright spots is really the heart of the issue. I understand the importance of Starlink; I can see the benefits of worldwide internet, says Tregloan-Reed. Its just the sheer numbers that are worrying me.

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The true impact of SpaceXs Starlink constellation on astronomy is coming into focus - The Verge

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