Imaging the Lunar Eclipse

Posted on December 21, 2010 by The National Air and Space Museum

I was pleasantly surprised when the clouds rolled out and the weather turned out to be favorable for the total lunar eclipse last night! After work, I went home for a quick nap and put on layers and layers of clothing to help me brave the cold on the eve of the winter solstice. Friends and coworkers told me I was crazy to come back to work at midnight for the eclipse, especially with the temperatures predicted to be in the 20s. But the clear skies, which have been hard to come by so far this month, were more than this astronomy educator could resist.

So I met fellow astronomy educator Erin Braswell at National Air and Space Museum’s Public Observatory at 1 a.m. to begin preparations for a night of observing and imaging the lunar eclipse. Our goal was twofold: to experience the eclipse for ourselves, and to capture it to share with our colleagues and visitors.

The 16-inch Boller and Chivens which is the main telescope at the Public Observatory, is a very high-powered telescope, great for seeing the tiny details of the Moon’s craters and other features. However, it magnifies too much to see the entire Moon in one shot so isn’t a great choice for eclipse viewing or imaging. Instead, we used the Public Observatory’s TeleVue-85 refracting telescope along with a Lumenera 2-0 color camera and a Lumenera 2-2 monochromatic camera.

Lunar eclipse seen from The National Air and Space Museum's Public Observatory on the morning of December 21, 2010. Photos by Erin Braswell and Katie Moore.

The photograph, above, will give you a quick snapshot of our experience. If you observed the eclipse, you might notice that the photo does not do it justice. The human eye is much more capable of seeing a range of details and colors on the bright and the eclipsed portions of the Moon, while the camera can only detect one part at a time. In reality, the “dark” portion of the Moon is still easily visible to the naked eye, although noticeably fainter than normal. Our cameras only capture, the brighter, uneclipsed portions of the Moon during the partial phases. During totality, they capture the fainter, eclipsed Moon. In addition, the color is more vivid to the naked eye, during totality.

As predicted, during totality, the Moon was not uniform in brightness – it was slightly dimmer at the bottom, which was closer to the center of the Earth’s shadow. Also, since the Moon didn’t pass through the middle of the Earth’s umbra, the eclipse doesn’t progress straight across the Moon.

The things I most enjoy about lunar eclipses are seeing such a familiar object as the Moon take on an unusual appearance, and thinking about how our closest celestial neighbors are arranged to make it happen. The Sun’s rays usually illuminate the Moon directly, but during a lunar eclipse, the Earth gets in the way. This causes the partial stages of the eclipse. Here you can rediscover that the Earth is a spherical object when watching the curved shadow of the Earth moving across the Moon! Then, during totality, the Moon is illuminated by sunlight that seeps through the Earth’s atmosphere, giving it the fainter, reddish glow. You can almost feel the heavens line up!

Did you photograph the total lunar eclipse? We’d love to see the results! Upload your images to the Public Observatory Project’s group page on Flickr.

Katie Moore is an astronomy educator at the National Air and Space Museum

Total Lunar Eclipse

Posted on December 17, 2010 by The National Air and Space Museum

The Moon is one of the most easily recognized celestial objects and arguably the easiest one to observe. It is simple to view the changing phases from day to day, with your naked eyes. Binoculars or a telescope will reveal countless craters, ancient lava flows, and other intriguing lunar features. Of the handful of thrilling astronomical events a person can witness in their lifetime, such as meteor showers, planetary transits and oppositions and auroras, solar and lunar eclipses are a must-see.

During the waning hours of December 20th and into the early hours of December 21st, people in North America will have the chance to witness a total lunar eclipse. A total lunar eclipse occurs when the Sun, Earth, and Moon are precisely aligned and the Moon passes into the shadow of the Earth. In other words, the Earth is preventing sunlight from reaching the Moon. Although an eclipsed Moon is always full, a lunar eclipse will not occur every time there is a full Moon since the Moon’s orbit is slightly tilted compared to the plane in which Earth orbits the Sun. When the Moon reaches one of the two points in its orbit where it lines up exactly with the Sun and the Earth, either a solar or lunar eclipse will occur.

This shows the geometry of a lunar eclipse. When the Sun, Earth, and Moon, are precisely aligned, a lunar eclipse will occur. During an eclipse the Earth blocks sunlight from reaching the Moon. Earth creates two shadows: the outer, pale shadow called the penumbra, and the dark, inner shadow called the umbra. The eclipse is noticeable once the Moon enters the umbra.

A lunar eclipse is much easier to observe than a solar eclipse. To view a solar eclipse, one has to travel to a very specific location on Earth. For a lunar eclipse, anyone located on the night side of the Earth has the opportunity to observe it. North America will have the best seat in the house for this total lunar eclipse. Provided they have clear skies, viewers should be able to see the entire eclipse from start to finish. Observers in East Asia, Australia, and New Zealand will see the Moon rising during the eclipse while those in Europe, West Africa, and South America will see the Moon set during the eclipse.

To watch a lunar eclipse you don’t need to use a telescope or any special equipment; simply go outside and enjoy the view. The duration of this total lunar eclipse is approximately four and half hours. If you don’t want to be extremely tired at work or school on Tuesday by staying up for the entire event, you can still see different stages of the eclipse in just over an hours’ time. On the east coast of the United States, the lunar eclipse officially begins around 1 am on the morning of December 21^st. However, the exciting part of the eclipse won’t begin until a half hour later.

This is a sequence of images taken and arranged by amateur astronomer, Fred Espenak. During a total lunar eclipse, viewers will see the shadow of the Earth slowly move across the surface of the Moon, covering it. Totality occurs when the Moon is fully covered. After totality, the Moon slowly moves out of Earth's shadow. Courtesy of Fred Espenak.

A total lunar eclipse begins when the Moon enters the pale, outer portion of the Earth’s shadow, known as the penumbra. This causes a very subtle darkening of the Moon which is almost undetectable. The umbra is Earth’s dark, inner shadow where no direct sunlight reaches. When the Moon moves into the umbra, the partial eclipse begins, and you will begin to see a dark, curved shadow creep across the lunar surface. Partial eclipse begins at 1:33 a.m. on December 21^st for east coast viewers. Totality begins at 2:41 a.m. EST when the umbra has completely engulfed the Moon.

During totality, the Moon is still visible. Sunlight passing through Earth's atmosphere projects itself onto the lunar surface and casts it in an orange or reddish glow. Courtesy of Fred Espenak.

Despite not receiving any direct sunlight, the Moon will still be visible during totality, cast in an orange or reddish glow. This is due to scattered sunlight passing through Earth’s atmosphere and projecting onto the Moon. You have most likely seen this type of scattering of sunlight during brilliantly colored sunrises and sunsets. The color of the Moon during totality will depend on the clarity of the atmosphere during the time of the eclipse. If it’s clear, the Moon will have an orange tint. However, if there’s enough dust in the atmosphere (like from a volcanic eruption), the Moon might appear dark red, grey, or a reddish black.

This diagram shows the progression of the total lunar eclipse on December 20th and December 21st, 2010. Each number corresponds with the beginning of a specific stage in the eclipse. 1) Partial eclipse begins 2) Total eclipse begins 3) Mid-eclipse 4) Total eclipse ends 5) Partial eclipse ends. Moon images courtesy of Nathan S. Barrow. (Diagram created by Shelley Witte)

Totality will last 72 minutes and then the Moon will start to reemerge from the umbra — replaying the eclipse events in reverse. If you don’t have enough time or energy to watch the eclipse in its entirety, I recommend watching from partial eclipse until totality or vice versa. Check the chart below/above to find the times the lunar eclipse is visible from your neck of the woods.

North America will have a great view of the total lunar eclipse on December 20-21, 2010. Listed here are the times when viewers in the contiguous United States can observe the different stages of the eclipse.

If the skies are favorable during the night of the total lunar eclipse, take the opportunity to witness a fascinating celestial phenomenon; if you live in North America you won’t get to watch another one like this until April of 2014!

Planning on photographing the total lunar eclipse? We’d love to see the results! Upload your images to the Public Observatory Project’s group page on Flickr.

To see more eclipse imagery from Fred Espenak, please visit MrEclipse.com.

Shelley Witte is an astronomy educator at the National Air and Space Museum.

Learning to Capture the Sun

Posted on October 19, 2010 by The National Air and Space Museum

The Public Observatory Project is just over a year old now, and in that time we’ve been experimenting with the telescope to discover what is visible in the daytime sky and devise ways that our visitors can have the best experience possible. One of our goals is to use our equipment to take images of the Sun, so that we can share our star’s day-to-day activities with the visiting public as well as those who can’t make it to the Mall to look through our telescopes. We wanted to capture true-to-life images of the Sun as it appears through our telescope and make interesting features clearer and more apparent.

It would be dangerous to use a normal telescope to look at the Sun because the Sun’s concentrated and unfiltered light would damage your eyes. One of the tools we use to look at the Sun safely is our Lunt Solar Systems hydrogen-alpha telescope that filters out all but one wavelength of red light. This makes it safe for viewing a part of the Sun’s atmosphere, called the chromosphere. To take images of the Sun, I started out with this telescope, as well as a Lumenera SKYnyx 2-0 Color camera that fits where the eyepiece usually goes. We also have a laptop with software to control the camera, called Lucam Recorder. With these in hand, I set off to take some of my first images of the Sun.

This image of two prominences was taken on June 8, 2010.

Through some experimentation, I found out that different exposure settings revealed very different details on the Sun. First I cranked up the exposure to capture the faint prominences coming off the edge of the Sun and took a series of images. Next, I turned down the exposure to what I thought was an appropriate level to capture details on the Sun’s surface before taking a second series of images. I used a processing program called the GIMP to merge the two images by selecting the disk detail and moving it on top of the prominence image. But, something wasn’t quite right. This didn’t look much like what I was seeing with my own eyes. So, I turned to a local amateur solar imaging expert and friend of the National Air and Space Museum: Greg Piepol.

Greg’s solar imaging work, which you can check out on his website sungazer.net, has been praised for its beauty and attention to detail. My colleague at the Observatory and fellow Sun imager, Katie Moore, and I were thrilled that he agreed to come into the Museum and show us how he captures such stunning images.

Greg taught us several things that improved our imaging. The first and most important was that we had been drastically overexposing the disk of the Sun, which washed out the details we were trying to capture. Greg also taught us how to better use an image stacking program called Registax, which takes individual frames from a movie file and stacks them together, thereby removing a lot of noise caused by Earth’s turbulent atmosphere. Astronomers call this “seeing,” which is what makes the stars twinkle. He also showed us other image processing techniques in the GIMP, such as levels adjustment and color correcting that brought out details on the Sun.

This image was taken on July 28, 2010, the day after Greg Piepol came to visit. The small dark Sunspot near the top of the disk is about the same size as the Earth!

This was most certainly closer to what we had seen in the telescope. But of course, as they say, practice makes perfect. Over the next few months I took pictures as often as I could. I learned the extreme importance of making fine adjustments to the filters inside the telescope to get exactly the right details. I learned the advantages of using a double-stacked filter on top of our telescope to help make the darker wispy absorptive lines in the solar atmosphere, called filaments, truly pop out. I also learned the importance of careful processing to coax the most detail possible out of the raw data. It is interesting to compare the final product to one of the raw, unprocessed images to see what a difference it makes.

This is a single frame from the raw video before the image is processed

This final processed image of a Sunspot was taken on July 30, 2010

A large prominence on the Sun, taken on September 15, 2010

This mosaic of 2 images highlights a large Sunspot group, as well as a dark filament in the Sun’s chromosphere.

And so, the journey continues! The Sun is always changing, and there are always more techniques to be learned and perfected. If you get the chance, come see the Sun for yourself at the Public Observatory, which is open Thursday through Sunday, 11 am to 3pm for the month of October, weather permitting. We are ordering an upgraded camera and some new software to better process these images, so be on the lookout for new images online!

Erin Braswell is an Astronomy Educator at the National Air and Space Museum.

Seeing Beneath the Surface of the Moon

Posted on October 5, 2010 by The National Air and Space Museum

“Remote sensing” is a term used to describe many different types of observations carried out at a distance. Aerial photos, satellite images of the Earth and planets, and telescope views of our solar system are all forms of remote sensing used to understand geology, climate, hazards, and changes over time. Not all remote observations use the wavelengths of light visible to humans; there is a wealth of information contained in how a surface reflects or emits radiation across the spectrum from radio waves to gamma radiation. Scientists at the National Air and Space Museum’s Center for Earth and Planetary Studies use radar signals, transmitted from satellites in lunar orbit or from the largest radio dishes on Earth, to probe below the dusty surface of the Moon. Radio waves, which have a much longer wavelength than visible light (the Museum’s research uses signals with 12.6-centimeter and 70-centimeter wavelengths), penetrate up to 30-40 meters into dry material and reflect from buried layers or rocks suspended in the thick dust. By carefully measuring the time between the transmitted and received radar signals, and the subtle changes in frequency caused by the rotation of the Moon, the radar “echoes” can be assembled into an image that resembles a photograph, but revealing aspects of lunar geology often hidden from optical cameras. Studies using the new radar maps trace the outlines of ancient lava flows now buried by material hurled from giant impact craters, find rocky material in resource-rich areas that might pose hazards to robotic exploration, and “light up” for the first time areas near the poles that are in permanent shadow from the Sun. Ongoing work suggests that some areas of the smooth lunar “seas,” or maria, may have very rugged, boulder-covered lava flows hidden by billions of years of overlying dust; how such rough deposits might form remains a mystery. The lessons learned from studies of the Moon are guiding efforts to design a radar sensor for Mars that will look beneath that dust-covered surface to reveal additional geologic signatures of past and present water.

A 12.6-centimeter wavelength radar view of the lunar crater Aristoteles (87 km diameter). Rugged areas, such the northern interior wall of the crater, appear bright to the radar, and smooth or dusty parts of the surrounding region appear dark. The radar lighting comes from the lower left, so the walls of the crater cast "radar shadows" just as they would for illumination by the Sun. The surrounding clusters and chains of smaller craters were formed by debris ejected from the main crater.

Bruce Campbell is a geologist in the Center for Earth and Planetary Studies at the National Air and Space Museum.

A ‘Spectacular’ Hoax Continues to Fool E-mail Readers

Posted on August 13, 2010 by The National Air and Space Museum

As an astronomy educator here at the National Air and Space Museum, I’ve had the opportunity to interact with thousands of visitors, especially in our Public Observatory. I’ve enjoyed the many chances to discuss the wonders of the Universe and to answer visitors’ astronomy-related questions. However, I tend to dread the month of August because of an internet hoax involving Mars that’s been plaguing e-mail inboxes for seven years.

The e-mail in question is commonly referred to as the “Mars Hoax” or, more accurately, the “Mars Spectacular,” and is titled: “Two moons on 27 August or The Red Planet is about to be spectacular!”

It informs recipients that Mars will have an extremely close encounter with Earth during the month of August, culminating on August 27^th when Mars is approximately 34 million miles away. The information in the previous sentence was only true during the month of August in 2003. This was a historic astronomical event. Mars was the closest it had been to Earth in 60,000 years. However, this already happened.

Before I get into the e-mail’s misinformation, let’s talk about what actually happens when Earth and Mars have a close encounter. Imagine two people are running a race around a track. One person is running in the innermost lane while the other is running in the outermost lane. The runner in the inside lane will complete one lap faster than the other person. This is similar to Earth’s and Mars’ orbits around the Sun. Earth takes 365 days to complete a lap around the Sun while Mars completes a lap in 687 days. If the runners continue running, eventually the runner on the inside (Earth) will catch up with the runner on the outside (Mars). When this occurs in the solar system, it is called opposition. It also means that Mars is opposite of the Sun in the Earth’s sky. An opposition for Mars occurs approximately every 2 years. The last three occurred on November 7, 2005, December 24, 2007, and most recently on January 29, 2010.

An opposition occurs when the Sun, Earth and Mars line up with the Earth in the middle. This phenomenon, which happens every two years, brings Earth and Mars relatively close together. This diagram shows four recent oppositions and two future ones. The 2003 opposition was significant because Mars was very near its perihelion - the point in its orbit where it is closest to the Sun. At that time, Mars came within 35 million miles of Earth. Mars will be almost that close again during the opposition in July of 2018.

Why was the Mars opposition in 2003 so special? Most oppositions bring Earth and Mars between 34 and 63 million miles from each other. This is mainly due to Mars’ elliptical orbit. All planetary orbits are slightly elliptical meaning that a planet’s distance to the Sun changes as it moves in its orbit. When it’s closest, it’s called “perihelion” and when farthest, “aphelion.” Mars’ orbit is more elliptical than Earth’s. Every 15 to 17 years, Mars is in, or very close to, its perihelion point just as Earth “catches up” with Mars. This brings the two planets especially close together. In 2003, this perihelic opposition occurred on August 27, when Mars was closest to the Sun, and Earth near its most distant point from the Sun. This combination brought the Earth and Mars unusually close together. As a result, Earth and Mars were 34.6 million miles away from each other; the closest they had been in 60,000 years.

If you missed this historic event, you may be wondering what Mars looked like in the sky during August of 2003. According to the most recent versions of the Mars Spectacular e-mail, Mars will appear “as large as the full moon to the naked eye.” That’s huge! No wonder people are still excitedly forwarding this e-mail to everyone they know. The original e-mail, though, stated, “At a modest 75-power magnification Mars will look as large as the full Moon to the naked eye.” This is more or less true, just misleading. It’s referring to how Mars could appear if magnified 75 times by a telescope eyepiece. To see any significant detail on the Martian surface rather than a large, red, fuzzy blob one would have to peer through a telescope with an objective mirror or lens larger than 8 inches; a much larger telescope than what department stores sell.

On August 27, 2003, Mars appeared as a bright star in the night sky. Even during this record approach it did not appear as large or as bright as the full Moon. Photo credit: John Nemy & Carol Legate of Whistler, B.C.

To the naked eye, Mars appeared as a bright, reddish, star-like object during the 2003 opposition. It was twice as bright as Sirius, the brightest star in the night sky, but not quite as bright as Venus appears this month. Compared to the full Moon, Mars was only 1/75 of its size – certainly not a second Moon in the sky. Those who forward the Mars Spectacular e-mail probably don’t consider the implications of Mars appearing that large. Mars is around twice the size of our Moon. It would be have to be located at twice that distance (480,000 miles) for it to appear the same size – 33 million miles closer than it ever gets to Earth. If Mars does appear as our “second moon,” something has gone terribly wrong with the inner solar system or the laws of physics .

Some versions of the e-mail, referred to as the "Mars Spectacular" are in the form of a PowerPoint presentation. This particular (and completely untrue) slide has evolved from a misleading statement claiming that Mars will appear as large as the full Moon through a modest telescope.

The Mars Spectacular e-mail is still circulating. I know three people who received it in the past month from well-meaning relatives. One reason it still has life is because the actual year of the event was dropped from the e-mail text. Therefore, every August people receive this e-mail and believe Mars will be close to Earth that year. Unfortunately, “2010” has mysteriously appeared in recent versions of the e-mail which definitely does not allow the e-mail to go away quietly.

If you have received the Mars Spectacular e-mail, believed it to be true, and passed it along to friends, family, or perhaps even a news outlet, it’s okay. You’re not the first one to fall for its thrilling message and you certainly won’t be the last. A good lesson to come from the Mars Spectacular e-mail is: if it’s too fantastic to be true, it’s probably not. Being internet savvy means you know where to find trustworthy sources and can weed out the misinformation. To check the validity of e-mail content, one of the best online resources is Snopes. You’ll find the “Mars Hoax” in the #12 spot of their Hot 25 list of urban legends. NASA, as well as astronomy magazine sites such as Sky and Telescope and Astronomy are also good online astronomy resources.

Disappointed that you won’t be able to see a “spectacular” Mars? Don’t fret! Mars is viewable in the evenings throughout the month of August, 2010. It is currently low in the southwestern horizon after sunset, hanging out with Saturn and a very bright Venus. Check Sky & Telescope’s weekly “sky at a glance” page for observing tips and information on other astronomical events.