Category: Astronomy

A total eclipse of the Moon occurs during the night of Wednesday, February 20/21, 2008. But where will the action be? For viewers in South America and most of North American the entire event will be visible on the evening of February 20. For Western Europe, Africa, and western Asia, your opportunity to view the action will happen on the morning of February 21. During a total lunar eclipse, the Moon’s appearance can range from bright orange to blood red to dark brown and (rarely) very dark gray. What can we expect this time?

Making predictions about a total lunar eclipse’s appearance is based on understanding what makes it happen. During a lunar eclipse, the Earth passes between the Sun and the Moon, blocking the Sun’s light. We see the Earth’s shadow creep across the surface of the Moon. This shadow is made up of two cone-shaped parts, one nested inside the other. Earth’s outer shadow – the penumbra – is a zone where our world blocks some (but not all) of the Sun’s rays. The inner shadow cone – or umbra – is the region where all light is blocked. Logically it would seem like we’d see a lunar eclipse each time the Sun and Moon are at opposition… But why don’t we see one every lunar cycle?

The Moon’s orbital path around our Earth is tilted at about 5 degree angle to Earth’s orbit around the Sun. In other words, most of the time the Moon is just a little over, or a little under the plane of Earth’s orbit. Just like clockwork, our Earth is also orbiting the Sun and Earth’s shadow cones are located on exactly in the same plane. All we have to do is wait for them to intersect! How often does that occur? If we were to take a look at a 5,000 year span, we’d see there are 7,718 eclipse occurrences – both total and partial – with an average of one to two per year… or as many as 3! Watching this year’s February 20/21 eclipse is important because it will be the last totality event until December, 2010.

Now that we understand what makes it happen, let’s take a look at the reasons why a lunar eclipse can appear as so many colors. While every lunar eclipse appearance is different, the physics that govern them is the same. If our Earth didn’t have an atmosphere to bend the sunlight back towards the Moon, it would always become invisible during the umbral, or total phase of an eclipse. Suspended in our atmosphere is dust – one of the major reasons for eclipse coloration. The less dust, the lighter the colors. Heavy dust in our atmosphere causes not only spectacular sunrises and sunsets, but deep eclipses as well. As you enjoy the eclipse, think of what is really causing the incredible colors and subtle tones you’ll see… The combined effect of all the simultaneous sunrises and sunsets on Earth projected onto the Moon!

Lunar eclipses are particularly fun because they don’t require any special equipment to observe. However, if you use a pair of binoculars you can magnify the view and see the shadows race across the Moon’s surface. This eclipse will also a very good time for amateur astronomers to make great scientific observations as well! For visual observers, using the Danjon Brightness Scale for lunar eclipses, amateurs can categorize the Moon’s color and brightness during totality. It’s easy! Just remember these values:

• L = 0 Very dark eclipse, where the Moon is almost invisible, especially at mid-totality.
• L = 1 Dark Eclipse, gray or brownish in coloration and details on the surface are hard to see.
• L = 2 Deep red or rust-colored eclipse with a very dark central shadow, while the outer edge of umbra is relatively bright.
• L = 3 Brick-red colors and the umbral shadow usually has a bright or yellow rim.
• L = 4 Very bright copper-red or orange eclipse where the umbral shadow has a bluish, very bright rim.

If you have a telescope, you can do even more! By watching major craters, you can measure the exact time when each crater enters and leaves the umbral shadow and the timings can be used to estimate the enlargement of Earth’s atmosphere due to airborne dust and volcanic ash. These results can then be submitted to Dr. Richard Keen.

For now? It’s time to get ready… Because even more surprises are in store for this eclipse!

Because stars are just points of light in the sky, it’s very difficult to know how far away they are. Astronomers use several techniques to measure distance, but they’ve got a new one now. By measuring echos of light bouncing off a distant nebula, researchers have fine-tuned their accuracy to an amazing level of precision.

Astronomers used ESO’s New Technology Telescope at La Silla to perform detailed observations of a star called RS Pup. It’s a member of a group of pulsating stars known as Cepheid variables. RS Pup changes in brightness by a factor of 5 every 41.4 days. It’s 10 times more massive than the Sun, 200 times larger and puts out 15,000 times more light.

You can look through these books and instructional materials from Amazon.com for more information about stars.

Because Cepheids pulse at a rate in proportion with their size, astronomers can measure how far they are by how often they pulsate.

But this only tells you how far they are relative to one another. So astronomers use a different technique called parallax to measure distance as well. If you want more info on this, check an episode of Astronomy Cast where we measure different techniques to measure distance in the Universe.

Now astronomers have come up with a second technique to measure distance to a star like RS Pup; to confirm that the Cepheid variable technique is correct.

They did this by watching how light moves through the nebula of material shed by RS Pup in the past. Since light is going 300,000 km/s, it takes time to pass by various blobs of gas and dust in the nebula.

The researchers calculated the light curve from an event on the star, and then watched as that same curve passed different parts of the nebula. It was then a relatively straightforward calculation to determine how far away RS Pup is.

To really appreciate what’s happening, check out the video, where you can see pulses of light move through the nebula. I’ll warn you, it’s a 3.4 MB download.

According to their calculations, the star is 6,500 light-years away, give or take about 90 light years. It’s the most accurate distance to a Cepheid ever captured, with a 1% level of precision.

Original Source: ESO News Release

It’s a day meant for celebrating love, and what better way to mark the occasion than to take a look at asteroid Eros! While its mythical name is fitting of the holiday, exploring the famous asteroid went into history on February 14, 2000 when the NEAR spacecraft was successfully inserted into orbit around 433 Eros, becoming the first artificial satellite of an asteroid – an asteroid you can visit with just a telescope!

The Near Earth Asteroid Rendezvous mission had begun its journey on February 17, 1996 as the first of NASA’s Discovery missions to rendezvous with asteroid 433 Eros. During the journey to Eros, NEAR flew within 1212 kilometers of asteroid Mathilde on June 27, 1997 and was to continue onto Eros and obtain orbit in December of 1998. But, as luck would have it, a computer malfunction stopped the rendezvous burn of NEAR’s bipropellant engine and it flew past the asteroid on December 23, 1998. Mission operators quickly reprogrammed the spacecraft to obtain scientific flyby information and set up an orbit that would carry NEAR back to Eros in February 2000.

On the first Valentine’s Day of the new millennium, NEAR went into operation again about an hour after reaching its orbital destination and sent its own Valentine card back towards Earth – the first images of an asteroid taken from an orbiting spacecraft. Features as small as a 330 meters came to life and notably a prominent, sharp-rimmed crater which may have been caused by an impact. Inside the crater walls are subtle variations in brightness that hint at some layering of the rock in which the crater formed. Narrow grooves that run parallel to the long axis of Eros cut through the southeastern part of the crater rim. A house-sized boulder is present near the floor of the crater which appears to have rolled down the bowl-shaped crater wall. A large number of boulders are also seen in other areas of the old asteroid’s heavily cratered surface.

After a year orbiting Eros, NEAR was about out of fuel. Only designed to orbit the asteroid, the spacecraft wasn’t equipped to land and the plan was to simply let it eventually crash onto the surface. Having met all of its research objectives, scientists had a developed fondness for NEAR project and decided to try to land – a procedure which would allow them to test complex maneuvers and get close-up pictures of the surface. These pictures would allow scientists to see objects as small as 10 cm in diameter. The command was given and NEAR slowed its circular orbit and executed a series of braking turns as it approached the surface. The landing site was in the saddle-shaped middle of the asteroid where temperatures vary from 100 C during the day to -150 C) at night – a day that last less than five and half hours! Although the weak gravity only provided an escape velocity of a mere 22 mph, it held the survival ticket of the automobile-sized NEAR on February 12, 2001. Then the probe made space history by successfully landing atop the space rock, more than 316 million kilometers from Earth.

Why not celebrate this Valentine’s Day Anniversary by taking a look at Eros yourself? The 33 kilometer long, 13 kilometer diameter rock is the second largest near-Earth asteroid and is easily seen in larger backyard telescopes. Holding an average magnitude 11.5, you’ll find Eros hanging out in the circlet of Pisces just after sunset. For those with GoTo telescope systems or setting circles, finding Eros is as easy as entering RA 23h 20m 11s Dec 3°2’13”! Enjoy your journey to Eros tonight… and wish NEAR a happy anniversary!

According to this morning’s recent alert by Dr. David Dunham of IOTA, observers throughout the Americas, and even westernmost Europe, have a chance to observe an occultation of an 11.3-magnitude star in Gemini by far-flung 20000 Varuna on Sunday night, February 10-11, 2008. This trans-Neptunian object (TNO) may be as large as 1,000 kilometers across.

Those in South America are especially encouraged to try to observe this event, since they have the highest probability for an occultation. The nominal path misses the Earth to the south, but the real uncertainties in the prediction are hard to assess, as Steve Preston (International Occultation Timing Association) notes. So there’s a chance for an event even in North America.

Occultations of stars this bright by such large TNOs are quite rare; so far, none beyond those by Pluto/Charon have been observed. Even if an occultation by Varuna doesn’t occur, there could be an occultation by a possible satellite of Varuna.

Closest approach is at 4:26 Universal Time on February 11th in South America, and about 4:30 UT in North America. The formal uncertainty (1 sigma) in the time is about 5 minutes, but you should be prepared for at least a 3-sigma event. I would recommend monitoring/recording the star for at least 20 minutes before and after the predicted time for your station. If an occultation occurs, there will be a 9-magnitude drop lasting about 43 seconds for a central event. The star to be occulted is TYC 1913-00670-1 at right ascension 7h 18m 50.1s, declination +25° 43′ 19″ (equinox 2000.0). It lies 2.5° SSW of 5th-magnitude Iota (?) Geminorum and 1.3° WNW of 6th-magnitude 57 Geminorum. Detailed finder charts of different scales are on the event are located here. The site also has a view of the Earth as seen from Varuna that can be used to estimate your time of closest approach, as well as the altitude of the event above your horizon. Brian Skiff (Lowell Observatory) notes that the star to be occulted may be slightly fainter than given above, magnitude 11.9 rather than 11.3.

For more about observing occultations in general, check these articles – Reporting Your Observations. For occultations of stars by asteroids, we have special report forms (.xls versions preferred, but plain-text forms are available as well) here. Once you complete one of these forms, please send it to IOTA’s e-mail address for reporting asteroid-occultation observations. Additional resources for reporting your observations are available at the website of the North American Asteroid Occultation Program. Many thanks to Dr. David Dunham of IOTA for providing the information and please spread word of this event. Good luck with your observations!

If you live in the southern hemisphere, the Magellanic Clouds are a familiar sight. These are the closest, brightest examples of dwarf galaxies we can see from the Milky Way. Radio astronomers have discovered a tenuous stream of hydrogen connecting our galaxy together with the Magellanic Clouds. This stream will help astronomers calculate the motion of the Clouds. Have they been here for a long time, or are they just passing by.

The finger of hydrogen gas, called HVC306-2+230, is piercing through the disk of the Milky Way about 70,000 light-years away from our location. The exact point of contact is near the Southern Cross (you southerners know what I’m talking about).

Astronomers used to think that the Magellanic Clouds had orbited the Milky Way many times, slowly getting dismembered. But new observations from the Hubble Space Telescope showed that they’re actually moving much more quickly than previously believed. Instead of orbiting the Milky Way, they might just be passing us once, never to return.

By detecting where this leading arm strikes the Milky Way, astronomers will have an easier time calculating the Clouds’ trajectory.

“We think the Leading Arm is a tidal feature, gas pulled out of the Magellanic Clouds by the Milky Way’s gravity,” said Dr McClure-Griffiths, the research team leader from CSIRO’s Australia Telescope National Facility. “Where this gas goes, we’d expect the Clouds to follow, at least approximately.”

Their discovery actually strengthens the original theory, that the Clouds have been orbiting the Milky Way for a long time. Of course, the researchers caution that this isn’t the final word on the subject – the flyby model still hasn’t been ruled out.

But if they’re right, the Magellanic Clouds will eventually merge with the Milky Way and not zoom past.

Original Source: CSIRO News Release

While normally our friends in the Southern Hemisphere get left out of most major meteor showers, now is the time to keep alert for the Alpha Centaurids which are active during the entire month of February. While the Alpha Centaurids are considered a minor meteor shower, they do create some interesting viewing during the summer nights south of the equator. The peak (time of most activity) should occur around the universal date of Februrary 6/7, but don’t wait until then to start your observations!

According to the American Meteor Society:

“The Alpha Centaurids (ACE) are active from a radiant located at 13:44 (206) -58. This area of the sky is located in southeastern Centaurus, four degrees northwest of the brilliant star Hadar (beta Centauri). Current rates would be near one shower member per hour. These meteors are best seen near 0500 local standard time when the radiant lies highest above the horizon. This shower is not visible north of 32 degrees north latitude and also poorly seen in the northern tropics. The southern hemisphere offers a much better view of this activity as the radiant lies much higher in the southern sky. Those located at high southern latitudes will actually encounter morning twilight before the radiant reaches culmination. At 56 km/sec. the Alpha Centaurids will usually produce meteors of swift velocity.

Sporadic rates are now slowly falling no matter your location. One would expect to see approximately twelve random meteors during the last hour before dawn from rural observing sites in the northern hemisphere and fifteen from the southern hemisphere. During the first dark hour after the end of evening twilight, perhaps two random meteors can be seen per hour, no matter your location.”

While you’re out, take advantage of the opportunity to enjoy Centaurus! As one of the most inspiring constellations of the Southern Hemisphere, it also ranks as the ninth largest constellation and contains two of the ten brightest stars in the night sky – including the closest star to our own Sun. While the stargazers in the north rarely get an opportunity to explore the “Centaur”, nearly 2000 years ago precession allowed the ancient Greeks to observe the constellation during the spring. Even though they weren’t able to explore as we can today, they were still able to see Alpha and Beta Centauri, the third and tenth brightest stars in the sky. While many lists call Betelgeuse in Orion the tenth brightest star, remember… Betelgeuse is a variable!

Be sure to observe Alpha Centauri. One of the reasons it is so bright is not luminosity… but because it’s only 4.3 light years away. Rigel Kentaurius is a triple star system and a real beauty to binoculars and telescopes! Beta Centauri – Hadar – is a star on the move and in about 4000 years it will be close enough to Alpha to appear as a double star. While they won’t be gravitationally bound, a separation of 300 light years will make them a magnificent sight! Centaurus also contains Omega Centauri (NGC 5139), the largest and richest globular cluster in the sky. Centaurus also contains 20 open clusters and several galaxies including Centaurus A (NGC 5128), one of the brightest radio objects in the sky. While you’re there, be on the lookout because the a large portion of our own galaxy is also visible in Centaurus and there are over 100 easily visible stars.

Because you’re in for a moonless night and the days around the Centaurid Meteor shower peak will be of little moon-interference, this will be one of the best for Southern Hemsiphere SkyWatchers. If you live in the north? It never hurts to try. Even from my high latitude, I still get an occasional peek at some of Centaurus’ stars. Long noted for extremely bright meteors with persistent trails and flurries of high activity, I’m sure you’ll enjoy the incredible Centauri meteor shower!

While the penguins in Antartica will be putting on their formal wear for the annular solar eclipse, a few lucky SkyWatchers in New Zealand and southeast Australia will still have a chance to see the Moon take a bite out of the solar disc roughly between 01:38:29 and 06:11:55 a.m. GMT. The best place to be is Auckland, New Zealand, where the partial eclipse begins at about 4:48 p.m. (Pacific/Auckland) local time (3:48 a.m. GMT) and ends at about 6:51 p.m. (5:51 a.m. GMT), a little more than two hours later.

The first eclipse of 2008 will travel over Antarctica and the waters surrounding the continent – not a hospitable area for visitors! While there are no permanent human residents in these areas, that won’t stop some travelers from heading towards the barren southern pole to take a look at the annular event. Unlike a total solar eclipse, the New Moon won’t completely cover the solar disc at maximum and a thin ring of the outer fringes of the Sun will still be visible – the annulus. If you were to be in the direct path, you’d enjoy the incredible view of the annular phase from 03:19:43 to 04:30:55 a.m. Greenwich Mean Time (GMT).

Fortunately for those of us who aren’t wearing a permanent tuxedo, the best place to observe will be in Auckland, where the Sun will be covered about 47% at around 5:52 p.m. local time. Considering they’re still enjoying more summer-like weather, it’s time to party! According to Fred Espenak:

“The most unusual characteristic of this eclipse is that it begins and ends along Earth’s sunset terminator. Most eclipse paths that travel from west to east. However, the 2008 annular eclipse path begins by running east to west and slowly turns north before curving west to east near its terminus. The annular path begins in Antarctica at 03:20 UT when the Moon’s antumbral shadow meets Earth and forms a 581 kilometre wide corridor near the base of the continent’s peninsula region. Traveling westward, the shadow quickly crosses Antarctica and turns north as it heads into the Pacific. Greatest eclipse takes place at 03:55:05 UT when the eclipse magnitude will reach 0.9650. At this instant, the annular duration is 2 minutes 12 seconds, the path width is 444 kilometres and the Sun is 16° above the featureless horizon of the open ocean. The central track continues north before gradually curving to the east where it ends at local sunset at 04:31 UT. During its 1 hour 10 minute flight across our planet, the Moon’s antumbra travels approximately 5,600 kilometres and covers 0.59% of Earth’s surface area.”

Remember when viewing a solar eclipse, to always do so safely. If you do not have a proper solar filter, use the projection method with your binoculars or telescopes. Safely cover one side of your binoculars or telescope’s finderscope and aim towards the Sun by aligning the shadow. Project the light onto a surface such as a paper plate or piece of cardboard and adjust the focus until you see a clear circle of light. If you do not have optics, simply punch a pinhole into a dark piece of cardboard and project it onto a makeshift screen. You won’t see solar details like sunspots, but you’ll easily see the progress of the shadow!

Wishing you all clear skies… And share your photos!