Marshall Space Flight Center – Page 13

'Only' 14 Million Miles Away!

The skies were clear over New Mexico last night — Oct. 6, 2010 — so Rhiannon Blaauw of NASA’s Meteoroid Environment Office, Marshall Space Flight Center, Huntsville, Ala., captured this image of Comet Hartley 2 at a distance of “only” about 14 million miles from Earth.

Hartley 2 has passed out of the constellation Cassiopeia and is now traveling through the constellation Perseus. On October 20th, the comet will come within 11 million miles of Earth. Since comets rarely come this close, it will be faintly visible to the naked eye in the early morning sky. The comet has an orbital period — or time to travel once around the sun — of approximately 6.5 years.

For those interested in astronomy photography, the image was taken with a single shot color filter with 300-second exposure via a remote-operated telescope located in Mayhill, N.M.

We’re tracking Hartley 2’s journey as it approaches Earth, so stay tuned for more photos!

Image courtesy of Rhiannon Blaauw, NASA’s Meteoroid Environment Office, Marshall Space Flight Center, Huntsville, Ala.

Comet Hartley 2 Seen in Cassiopeia

In this image taken on the evening of Friday, Oct. 1, Comet Hartley 2 can be seen in the constellation Cassiopeia (north-east sky, not far from horizon).

Hartley 2 will only be in Cassiopeia for a few more day before traveling through the constellation Perseus. It’s a Jupiter Family Comet that we can’t see right now because it’s too tiny at approximately 1.2 km across. In this image, the comet was still 16,500,000 miles from Earth.

On October 20th, Hartley 2 will will come within 11 million miles of Earth, and since comets rarely come this close, it will be visible to the naked eye in the early morning sky. The comet has an orbital period, or time to travel once around the sun, of approximately 6.5 years.

For those interested in astronomy photography, the image was taken with a single shot color filter with 300-second exposure. It was captured by Rhiannon Blaauw of NASA’s Meteoroid Environment Office, Marshall Space Flight Center, Huntsville, Ala., via a remote-operated telescope in Mayhill, N.M.

We’ll be keeping an eye on Hartley 2 as it approaches Earth, so stay tuned for more photos!

Images courtesy of Rhiannon Blaauw, NASA’s Meteoroid Environment Office, Marshall Space Flight Center, Huntsville, Ala.

Fireball in the Sky!

It was brief, but it was brilliant! On Saturday, Oct. 2, 2010 at approximately 8:50 p.m. CDT, cameras operated by NASA’s Meteoroid Environment Office at Marshall Space Flight Center in Huntsville, Ala., recorded a slow moving fireball moving from the north to the southwest.

Enhanced-color image of Alabama fireball meteor.

The fireball was moving approximately 35,300 mph (15.8 km/s). It appeared at an altitude of 45.5 miles (73.2 km) and ablated, or burned up, at an altitude of 25.3 miles (40.7 km). The meteor experienced significant deceleration as it entered the atmosphere, resulting in a meteor trail that lasted about three seconds, seen in the movie below:

Using data from cameras at both Huntsville and Chickamauga, Ga., astronomers at the Marshall Center determined that the meteor was located over Marion County, Ala.

Diagram of fireball’s path over Marion County, Ala.

Images and video courtesy of Danielle Moser, NASA’s Meteoroid Environment Office, Marshall Space Flight Center, Huntsville, Ala.

Here Comes Comet Hartley 2!

A pale green interloper among the stars of Cassiopeia, Comet Hartley 2 shines in this four-minute exposure taken on the night of Sept. 28, 2010, by NASA astronomer Bill Cooke:

Still too faint to be seen with the unaided eye, the comet was 18 million miles away from Earth at the time. Cooke took this image using a telescope located near Mayhill, N.M., which he controlled via the Internet from his home computer in Huntsville, Ala.

Comet-watching from the comfort of your living room! Modern astronomy is truly amazing…

More About Comet 103P/Hartley 2

Comet 103P/Hartley 2, a small periodic comet, was discovered in 1986 by Malcolm Hartley, an Australian astronomer. It orbits the sun about every 6.5 years, and on Oct. 20, the comet will make its closest approach to Earth since its discovery. In this case, “close” means 11 million miles, or 17.7 million kilometers. A moonless sky will make for promising viewing conditions in the northeastern skies, especially just before dawn.

Comet Hartley 2’s nuclear diameter is estimated at 0.75-0.99 of one mile — 1.2-1.6 kilometers — and it’s believed to have enough mass to make approximately 100 more apparitions, or appearances, near Earth. The 2010 appearance also marks one of the closest approaches of any comet in the last few centuries.

Images courtesy of Bill Cooke, NASA’s Meteoroid Environment Office, Marshall Space Flight Center, Huntsville, Ala.

When to look? In what direction?

Lots of questions coming in, so I thought I would deal with them here.

I live in xxx… Can I see Perseids?

Check out the map below. Unless you live in the red shaded area, you will be able to see the shower. EVERYONE in the United States and Europe with clear weather will be able to see it, provided they are away from city lights and have clear, dark skies. Most other parts of the world will be able to see the shower as well.

When do I look?

You should start to see Perseids around 10 PM local time. The rate will increase throughout the night until just before dawn (3 to 4 am), when you may be able to see as many as 80-100 per hour. Be sure to allow about 45 minutes to allow your eyes to dark adapt.

Where do I look?

Lie on your back on a sleeping bag, blanket, or lawn chair and look straight up and take in as much sky as possible. Do not look at the constellation Perseus, where is the shower radiant is located, as you will see fewer meteors. This is because the length of the meteor gets longer the farther it appears from the radiant; to see nice bright meteors, you need to look some distance away from Perseus, which for U.S. observers is off to the northeast. Looking straight up, towards the Zenith, is a good choice and enables you to take in a lot of sky.

Do not use binoculars or a telescope, as they have narrow fields of view and will greatly reduce your chances of seeing meteors.

Hope this helps and wish everyone lots of meteors!

Will the Perseid shower be visible from {insert your location}?

I am asked this question over and over again, and it’s a good one. Everyone knows that you have to be in the right place to observe solar eclipses and other astronomical goings-on, so why should meteor showers be any different?

You do have to be in the right part of the planet to view meteor outbursts or storms, because the trails of comet debris are so narrow (hundreds of thousands of miles) that it only takes a few hours for the Earth to pass through the stream. A few hours is not enough time for the Earth to do a complete rotation (which takes 24 hours), so only those people located in areas where it is night and where the radiant is visible will be able to see the outburst or storm. These dramatic events require the viewers to be in the right ranges of both latitude AND longitude.

This is not true for normal meteor showers, like this year’s Perseids. The main stream of particles extends for millions of miles along Earth’s orbit, requiring days for it to cross. All we need is one day to take the longitude out of the visibility calculations, because then the entire planet will experience night while the shower is still going on. That’s the good news.

The kicker is that we not only have to have darkness, but also the radiant — in this case, located in the constellation of Perseus — has to be visible, i.e. above the horizon. The elevation of the radiant depends in part on latitude of the observer, and one can derive — or look up, in this age of Google — a relatively simple equation that gives the maximum elevation of the radiant:

maximum elevation = 90 – |dec -lat|

where dec is the declination of the radiant and lat is latitude of the observer (all in degrees). The vertical lines before dec and after lat mean to take the absolute value of dec — lat. In order to see meteors from the shower, the maximum elevation must be 0 or greater (preferably more than 15 degrees). In the case of the Perseids, dec = 58 deg, so it is easy to calculate the maximum elevation for various latitudes:

We see that everyone in the northern hemisphere has a shot at seeing Perseids (weather permitting), but folks south of -32 degrees latitude get the shaft.

On the world map above, the red shaded area is the region where the Perseids will not be visible. If you live south of Brazil, at the very southern tip of Africa, or southern Austrailia, you need to take a road trip to the North if you wish to see Perseids. If you want see decent numbers, it will be a long ride, as you need to trek to somewhere above -17 degrees latitude.

So will I see Perseids? You can find out on your own — look up your latitude (remember, Google is your friend), use the equation above, stick in 58 degrees for the dec, and calculate the maximum elevation. If it is above 15 degrees, you are good.

Remember to get away from city lights. A dark sky is important.

Enjoy the show!

How low can they go?

Real-life meteor showers are not like what you see in movies — there are no flaming rocks barreling out of the sky blasting holes in buildings, or sending cars hurling many yards through the air. Most meteor showers are caused by debris left behind by comets, icy particles mixed with dust and organics that stand no chance of surviving their kamikaze death dives through Earth’s atmosphere. The meteors that actually do make it through, becoming meteorites when they strike ground, are very, very few in number and originate from asteroids (and much more rarely, Mars and the Moon). There are only a handful of recorded falls each year.

So how low can a Perseid get? The NASA all-sky cameras can provide the answer, at least for the bigger Perseids (inch or so across); the smaller particles burn up higher. Our two station camera network can determine the trajectory of a meteor through triangulation, and tell us the start height of the meteor (the location where it is first seen) and its end height (the location where it disappears or “burns up”). Both cameras observed 80 Perseids last year and 24 so far this year, which gives us enough data to tackle the problem.

We start out by taking the end heights of the Perseids and throwing them into 1 mile wide altitude bins. This results in the following graph:

Looking at the plot, it is apparent that most large Perseids burn up at about 56 miles (90 km) altitude. Some ablate as high as 65 miles (104 km), whereas others may get as low as 47 miles (76 km) altitude. We see none getting down to 45 miles or lower, which gives this old ground dweller a warm fuzzy feeling — I can enjoy the shower, secure in the knowledge that the meteors are going poof way up there.

It turns out that our friends the Perseids don’t get very low at all, ending their interplanetary journeys at least 46 miles above our heads.