Universe Today

September 27, 2009April 26, 2016 by Abby Cessna

Summer Solstice

Semi Major Axis — Solstice and Equinox - Credit: NASA

The summer solstice occurs once a year, and there is also a winter solstice each year. During both solstices, the tilt of the Earth’s axis is at its extreme either toward or away from the Sun. The tilt of the Earth does not actually change – it stays at 23.5° – however, the Earth also orbits the Sun causing different regions to be exposed to varying degrees of sunlight.

The word “solstice” has its roots in Latin from the words for “sun” and “to stand still.” This is because during the solstices, the Sun appears to stand still, and then it starts moving in the opposite direction in our sky. It begins to get lower in the sky, and the length of daylight starts getting shorter in the Northern Hemisphere.

In addition to the two solstices, there are also two equinoxes, which is where the days are of equal length at the equator. The tilt of the Earth is also responsible for the change in seasons we experience. During the summer solstice, the Suns is directly over the Tropic of Cancer.

The summer solstice is the longest day of the year – the longest time there is daylight – in the Northern Hemisphere. It is the opposite in the Southern Hemisphere however with the winter solstice being the longest day of the year. The exact date of the summer solstice moves around somewhat because of the way years are set up in the Gregorian calendar. For example, it fell on June 20th in 2000. Usually, however, it is on June 21st.

In some cultures, the solstices, and the equinoxes, represent the start of the seasons while they are the midpoint in other cultures. The summer solstice is the beginning of summer in America. The summer solstice has long been a time for celebration for many different cultures. Midsummer was a holiday celebrated in various European cultures.

Traditionally, Midsummer’s Day falls on June 24th, several days after the actual solstice. The Midsummer celebration of the ancient Gauls was known as the Feast of Epona. In China, the summer solstice celebration represented yin, earth, and the feminine while its opposite – the yang – was celebrated during the winter solstice.

Germanic, Slav, and Celtic tribes in Europe used to celebrate Midsummer with huge bonfires. Jumping through the fire was supposed to grant protection to people and bring love. The bonfires were also supposed to lend their power to the Sun, which would begin to wan as winter approached.

Universe Today has articles on the shortest day of the year and the declination of the Sun that will help you learn more about the solstices and seasons.

If you are looking for more information, About.com has a number of good articles on the summer solstice and Science World has some great articles and resources.

Astronomy Cast has an episode on Earth you will want to check out.

September 27, 2009April 26, 2016 by Abby Cessna

Astrolabe

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An astrolabe is an ancient tool used in solving problems that involve time and the position of the Sun and stars. Astrolabes can be used in timekeeping, surveying, geography, and astronomy to name a few disciplines. One of its most well-known uses is navigation. Using an astrolabe, you can determine how the sky looked at a certain point in time at a specific place. Since it really is a visible map of the sky, it has proven extremely helpful in astronomical equations.

The astrolabe was invented sometime around 200 BC, and the Greek astronomer Hipparchus is often credited with its invention. A number of Greek scholars wrote in-depth treatises and texts on the astrolabe. Eventually, the tool was introduced to scholars in the Islamic world. They soon started using the instrument, mainly for navigation, and wrote many texts on the instrument themselves. Texts were also written on the subject in India, showing the extent to which this tool was used around the world.

The astrolabe is constructed of a hollow disk that is known as the “mater.” The mater can hold several flat plates that are known as “tympans” or “climates.” Each tympan is made for a specific latitude. The mater is marked indicating hours, degrees, or both measurements. The rete is the actual map of the ecliptic plane and has several pointers to indicate the brightest stars. You can think of the rete as a star chart. Often, different scales are engraved on the back of the mater to help in calculations. The engravings differed, and some of them included trigonometric scales and a calendar to convert between the day of the month and the position of the Sun according to the astrolabe. The alidade is attached to the back of the astrolabe. The alidade is used to take a star’s altitude.

The first universal astrolabe was invented by the Islamic scholar Abu Ishaq Ibrahim al-Zarqali. Unlike its predecessors, this astrolabe could be used at any location around the world instead of only at a specific latitude.

There are a number of astrolabe collections around the world, and you can still purchase astrolabes from a variety of locations. A later variation of the astrolabe is the spherical astrolabe, which looks like a sphere surrounded by a number of rings. The spherical astrolabe was also used in astronomy. The astrolabe is a predecessor of the sundial, which is still common today as an ornament in many gardens.

Universe Today has a more in-depth article on the armillary sphere and one on ancient astronomy.

For more information on astrolabes, you may want to check out astrolabes and the mariner’s astrolabe.

Astronomy Cast has an episode on choosing and using a telescope.

Source:
Wikipedia

September 27, 2009December 21, 2015 by Nancy Atkinson

Podcast: Atmospheres

Take a quick breath. There, that’s what we’re going to talk about today – the atmosphere. And not just the Earth’s familiar atmosphere, but the strange, exotic and deadly atmospheres we find in the Solar System and surrounding extrasolar planets.

Click here to download the episode.

Or subscribe to: astronomycast.com/podcast.xml with your podcatching software.

Atmospheres show notes and transcript.

September 25, 2009April 26, 2016 by Brian Ventrudo

A Prototype Detector for Dark Matter in the Milky Way

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It doesn’t emit electromagnetic radiation and no one really knows what it is, but that hasn’t stopped a team of European researchers from developing a device which scientists will use to detect and determine the nature of the dark matter that makes up 1/4 of the mass of our universe.

The researchers from the University of Zaragoza (UNIZAR) and the Institut d’Astrophysique Spatiale (IAS, in France), made assumptions about the nature of dark matter based on theoretical studies, and developed device called a “scintillating bolometer” to detect the result of interaction of dark matter with material inside the detector.

“One of the biggest challenges in Physics today is to discover the true nature of dark matter, which cannot be directly observed – even though it seems to make up one-quarter of the matter of the Universe. So we have to attempt to detect it using prototypes such as the one we have developed”, Eduardo García Abancéns, a researcher from the UNIZAR’s Laboratory of Nuclear Physics and Astroparticles, tells SINC.

García Abancéns is one of the scientists working on the ROSEBUD project (an acronym for Rare Objects SEarch with Bolometers UndergrounD), an international collaborative initiative between the Institut d’Astrophysique Spatiale (CNRS-University of Paris-South, in France) and the University of Zaragoza, which is focusing on hunting for dark matter in the Milky Way.

The scientists have been working for the past decade on this mission at the Canfranc Underground Laboratory, in Huesca, where they have developed various cryogenic detectors (which operate at temperatures close to absolute zero: ?273.15 °C). The latest is a “scintillating bolometer”, a 46-gram device that, in this case, contains a crystal “scintillator”, made up of bismuth, germinate and oxygen (BGO: Bi4Ge3O12), which acts as a dark matter detector.

Naturally, to build any type of dark matter detector, the researchers had to make some assumptions about the nature of the dark matter itself. The detection technique developed by the researchers is based on a number of theoretical studies which point to particles called WIMPs (Weakly Interacting Massive Particles) as the main constituent of dark matter.

“This detection technique is based on the simultaneous measurement of the light and heat produced by the interaction between the detector and the hypothetical WIMPs which, according to various theoretical models, explain the existence of dark matter”, explains García Abancéns.

The researcher explains that the difference in the scintillation of the various particles enables this method to differentiate between the signals that the WIMPs would produce and others produced by various elements of background radiation (such as alpha, beta or gamma particles).

In order to measure the miniscule amount of heat produced, the detector must be cooled to temperatures close to absolute zero, and a cryogenic facility, reinforced with lead and polyethylene bricks and protected from cosmic radiation as it housed under the Tobazo mountain, has been installed at the Canfranc underground laboratory.

“The new scintillating bolometer has performed excellently, proving its viability as a detector in experiments to look for dark matter, and also as a gamma spectrometer (a device that measures this type of radiation) to monitor background radiation in these experiments”, says García Abancéns.

The scintillating bolometer is currently at the Orsay University Centre in France, where the team is working to optimise the device’s light gathering, and carrying out trials with other BGO crystals.

This study, published recently in the journal Optical Materials, is part of the European EURECA project (European Underground Rare Event Calorimeter Array). This initiative, in which 16 European institutions are taking part (including the University of Zaragoza and the IAS), aims to construct a one-tonne cryogenic detector and use it over the next decade to hunt for the dark matter of the Universe.

Source: FECYT (Spain)

September 25, 2009December 24, 2015 by Jean Tate

Ecliptic

Zodiacal light can be seen in the sky before sunrise or after sunset. Credit: Yuri Beletsky/ESO Paranal

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Imagine you could see the position of the Sun, in the sky, relative to the stars (and galaxies, and quasars, and …). If you could, and if you plotted that position throughout the year you’d get a line; that line is called the ecliptic.

And why is it called the ecliptic? Because when the new or full Moon is very close to this, there will be an eclipse (of the Sun, and Moon, respectively).

The Earth goes round the Sun, in an orbit. That orbit defines a plane, which is an infinite two-dimensional sheet; the plane of the ecliptic.

The other planets in the solar system orbit the Sun in planes too, but those planes are slightly tilted with respect to the plane of the ecliptic … so transits of Venus (across the Sun) are quite rare (most times Venus passes either above or below the Sun, when it’s between Earth and the Sun). Mutual transits and occultations of planets are even rarer.

If you’re in a location relatively free of light pollution, on a clear, moonless night you may see zodiacal light. If you trace a line through the middle of it, you’re tracing the ecliptic (zodiacal light is due to reflection of sunlight off dust; dust in the solar system is concentrated in a plane close to the ecliptic plane).

Today astronomers use equatorial coordinates to give positions on the sky, right ascension (RA) and declination (Dec); these are like projections of longitude and latitude out into space (or onto the celestial sphere). However, in Europe ecliptic coordinates were used (up to the 17th century anyway). Here’s a curious fact: historically, Chinese astronomers used equatorial coordinates!

Universe Today stories: Plane of the Ecliptic, Vernal Equinox – Busting the Myth of Balancing Eggs, and Find the Zodiacal Light.

More: Astronomy Cast on Orbit of the Planets, and a Glow After Sunset.

September 25, 2009December 24, 2015 by Jean Tate

Altazimuth

Radio Telescopes. Credit: University of Washington

Altazimuth is a contraction of altitude-azimuth; in astronomy it most often refers to a type of telescope mount (and is sometimes called alt-az), but it can also mean a coordinate system.

Altitude means the angular distance above the horizon; straight up (overhead) is 90^o (and is called the zenith). Azimuth is also an angular distance, measured clockwise from north (so east is 90^o). Any point, or direction, in the sky has one – and only one – altitude and azimuth; in other words, the altitude and azimuth are the coordinates of the point (on the celestial sphere).

An altazimuth telescope mount is one that can move separately in altitude (up and down, vertically) and azimuth (side to side, horizontally). Small telescopes used by amateur astronomers tend to have altazimuth mounts; larger ones tend to have equatorial mounts … unless they are Dobsonian. Why? Because while alt-az mounts are generally cheaper, tracking astronomical objects (like stars) is much easier with equatorial mounts.

Historically, the telescopes used by professional astronomers did not have alt-az mounts, because automatic tracking was impossible. As computers became powerful and cheap enough, they could be used to control the motors on each axis of an altazimuth mount; today, almost all ground-based astronomical telescopes have altazimuth mounts, whether optical, radio, or even high energy gamma ray! The first really large optical telescope to use an altazimuth mount is the 6-meter Bol’shoi Teleskop Azimultal’nyi, in Russia.

Universe Today’s Telescope Mount, Telescope Parts, Telescope Tripod, and How To Use a Telescope are great resources for learning more.

The Astronomy Cast episode Choosing and Using a Telescope covers the benefits of alt-az mounts (vs equatorial), and Telescopes, the Next Level gives insight into tomorrow’s professional ones.

September 25, 2009December 24, 2015 by Nancy Atkinson

From Space: Huge River of Dust Over Australia

A river of dust over Eastern Australia on Sept. 24, 2009. NASA image courtesy Jeff Schmaltz, MODIS Rapid Response Team at NASA GSFC. Caption by Holli Riebeek.

[/caption]This isn’t a special effect image from a new catastrophe movie; it is an actual satellite image of the dust storm sweeping over and around eastern Australia, heading across the Tasman Sea toward New Zealand. A dense wall of dust descended upon Sydney on Sept. 23, creating an apocalyptic scene (see these images from Boston Globe’s Big Picture) and the river of dust continues unabated across water. The Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Terra satellite captured this image of the storm on September 24, at 11:10 a.m., New Zealand time (23:10 UTC on September 23). The distance between the far northern edge of the plume and the southern edge is about 3,450 kilometers (2,700 miles), roughly equivalent to the distance between New York City and Los Angeles. Below, see how the storm progressed across the Sea later in the day.

Dust storm over Australia during the afternoon of Sept. 24, 2009. NASA image courtesy Jeff Schmaltz, MODIS Rapid Response Team at NASA GSFC.

By the early afternoon of September 24, 2009, when the same satellite acquired this image, the thick dust that had covered the eastern shore of Australia previouly, stretched in a long plume from northern Queensland to New Zealand. This image shows the northern portion of the plume off the coast of Queenland. The tan dust is densely concentrated in a compact plume that mirrors the coastline. The gem-like blue-green Great Barrier Reef is visible beneath the plume near the top of the image where the tan dust mingles with gray-brown smoke from wildfires.

Source: NASA Earth Observatory

September 25, 2009December 24, 2015 by Fraser Cain

NASA Pictures

NASA has the absolute best resources on the web for pictures of space. We write so many articles about space here on Universe Today, so we’ve learned all the best places to look to get the latest and greatest NASA pictures.

Before we go right to some sites, here’s a general tip that you can use when you’re looking for NASA pictures. Use Google, but have it search for images within NASA’s sites. For example, let’s say that you’re looking for an astronomy picture of Mars, but you want it to be a NASA image. Search in Google for: mars picture site:nasa.gov. You can also switch over to the images tab and see lots and lots of images from NASA. You should be able to find the one you’re looking for.

Perhaps the best place to start is NASA’s Featured Images and Galleries. This is linked from the main NASA page and features current pictures as well as classics from the past. It also links you to other NASA image gallery sites.

Another classic is the Astronomy Picture of the Day. Keep in mind that although it’s endorsed by NASA, the pictures featured in Astronomy Picture of the Day are owned and copyright by the original photographers. So you can’t just use their pictures without asking permission first.

There’s a fairly new service out called NASA Images. It’s got a huge catalog of NASA pictures, with cool tools that let you organize and download your favorites.

The NASA Image Exchange is a huge database of NASA pictures. You can search by object, or by spacecraft and use other constraints to find the exact image you’re looking for.

The Johnson Digital Image Collection has photographs from all of NASA’s human spaceflight, from the original Mercury and Gemini flights, though the Apollo landings, right up until the space shuttle missions.

And if you want pictures of Earth, check out NASA’s Visible Earth site or the NASA’s Earth Observatory.

If you want pictures from the Hubble Space Telescope, here’s their homepage HubbleSite.

Want NASA photos from specific spacecraft? Here’s NASA’s Cassini spacecraft, here are the Mars Exploration Rovers, and here’s Mercury MESSENGER.

That should get you started.

We have written many articles about NASA and its photography here on Universe Today. Check out this gallery of images from the STS-127 shuttle mission. And here are images from the shuttle mission to repair the Hubble Space Telescope.

We have also recorded many episodes of Astronomy Cast about space, and we talk about NASA pictures all the time. Listen to this, Episode 88: The Hubble Space Telescope.

September 25, 2009December 24, 2015 by Tammy Plotner

Infrared Moonset

When it comes to the Moon, there are times when I feel like the “Queen of Selene”. In just a few short weeks there will be a whole new style of lunar observing book out on the market, and just when I thought I’d heard it all and seen it all… along comes something new! While the header photograph on this article is absolutely spectacular, you’re going to go about your day (and night) smiling if you stop to take a look at what’s inside…

After spending an entire weekend with close friend, professional astronomer and member of the USGS team – Brent Archinal – who has been mapping out the information from the LRO, I’ve been in a real “Moon” mindset. Even our UT articles have seemed to have been geared towards our nearest astronomical neighbor, too! So, it just stands to reason that others might be feeling the call of lunacy as well. As it just so happens, one of the most prolific, dedicated and innovative astrophotographers I know – Joe Brimacombe – wasn’t cursing the Moon for re-appearing this month… He was celebrating it. Using a variety of techniques, he’s captured one of the most unique sets of sequences I’ve ever seen and I just had to share it with you!

“On the 20th September 2009 a crescent Moon set over the mountains behind Cairns and was captured in all its glory from Coral Towers Observatory using a variety of infrared cameras.” said Dr. Brimacombe, “These recordings not only show a majestic Moonset, but also the dramatic retrograde motion of the Moon against the fixed background of stars over a mere six minute period.”

This is simply one of those videos that were too good to go left unnoticed. Not only did it appeal to my scientific side, but it totally restored my faith that others can not only be creative and innovative – but know how to have fun, too!

I hope you enjoyed…

“Infrared Moonset” photo and video are courtesy, credit and copyright of Joe Brimacombe – Southerngalactic Imagers.

September 25, 2009December 24, 2015 by Tammy Plotner

Weekend SkyWatcher’s Forecast – September 25-27, 2009

Greetings, fellow SkyWatchers! We’re back and recovered from a star party – and what an awesome time! (I felt like Dorothy in the “Land of Oz”… Comets and meteors and galaxies… oh, my!) I am sure that many of you also enjoyed a great time and although the Moon is back on this weekend scene, why not celebrate it? Just how long has it been since you’ve kicked back and relaxed with a little lunacy in your scope? Pick up a sketchbook, or get creative with a camera! Lunatic fringe? I know you’re out there. And I’ll see you inside…

Friday, September 25, 2009 – Today we celebrate the 1625 birth on this date of Ole (Christensen) Romer. Romer, by timing Jupiter’s moons being eclipsed, was the first to prove that light had a finite speed. Let’s walk upon our own Moon this evening as we take a look at sunrise over one of the most often studied and mysterious of all craters, Plato. Located on the northern edge of Mare Imbrium, and spanning 95 kilometers in diameter, Class IV Plato is simply a feature that all lunar observers check because of the many reports of unusual happenings. Over the years mists, flashes of light, areas of brightness and darkness, and the appearance of small craters have become a part of Plato’s lore.

On October 9, 1945, an observer sketched and reported ‘‘a minute but brilliant flash of light’’ inside the western rim. Lunar Orbiter 4 photos later showed where a new impact may have occurred. Although Plato’s interior craterlets average between less than 1 and up to slightly more than 2 kilometers in diameter, many times they can be observed, and sometimes they cannot be seen at all under almost identical lighting conditions. No matter how many times you observe this crater, it is ever-changing and very worthy of your attention!

Saturday, September 26, 2009 – Tonight’s featured lunar crater will be located on the south shore of Mare Imbrium right where the Apennine mountain range meets the terminator. Eratosthenes is unmistakable at 58 kilometers in diameter and 375 meters deep.

Named after the ancient mathematician, geographer, and astronomer Eratosthenes, this splendid Class I crater will display a bright west wall and a deep interior, which contains its massive crater-capped central mountain reaching up to 3,570 meters high! Extending like a tail, an 80-kilometer-long mountain ridge angles away to the southwest. As beautiful as Eratosthenes appears tonight, it will fade away to total obscurity as the Moon becomes more nearly full. See if you can spot it in 5 days!

Now let’s journey to a very pretty star field as we head toward the western wingtip of Cygnus, to have a look at Theta, also known as 13 Cygni (RA 19 36 26 Dec +50 13 15). Theta is a beautiful main sequence star that is also considered by modern catalogs to be a double. For large telescopes, look for a faint (13th magnitude) companion to the west. But it’s also a wonderful optical triple! In the field with Theta to the southeast is the Mira-type variable R Cygni, which ranges in magnitude from around 7–14 in slightly less than 430 days. This pulsating red star has a really interesting history that can be found at American Association of Variable Star Observers (AAVSO) and is circumpolar for far northern observers. Check it out!

Sunday, September 27, 2009 – Today we celebrate the 1814 birth on this date of Daniel Kirkwood. In 1866, this American astronomer was the first to publish his discovery of gaps in the distances of asteroids from the Sun, the ‘‘Kirkwood Gaps.’’ Not only did he study the orbits of asteroids, but he was also the first to suggest that meteor showers were caused by orbiting debris from comets. Known as ‘‘the American Kepler,’’ Kirkwood went on to author 129 publications, including three books.

Tonight on the Moon, let’s take an in-depth look at one of the most impressive of the southern lunar features—Clavius. Although you cannot help being drawn visually to this crater, let’s start at the southern limb near the terminator and work our way up.

Your first sighting will be the large and shallow dual rings of Casatus, with its central crater, and Klaproth adjoining it. Further north is Blancanus, with its series of very small interior craters, but wait until you see Clavius. Caught on the southeast wall is Rutherford, with its central peak, and crater Porter on the northeast wall. Look between them for the deep depression labeled D. West of D you will also see three outstanding impacts: C, N, and J; CB resides between D and Porter. The southern and southwest walls are also home to many impacts, and look carefully at the floor for many, many more! Clavius has been often used as a test of a telescope’s resolving power to see just how many more craters you can find inside it. Power up and enjoy!

This week’s awesome photos are (in order of appearance): Plato area (credit—Sketch by Deirdre Kelleghan), Eratosthenes (credit—Alan Chu), Theta Cygni (credit—Palomar Observatory, courtesy of Caltech), Daniel Kirkwood (widely used public image) and Clavius (credit—Wes Higgins). We thank you so much!