Brilliant Mars opening act for upcoming total lunar eclipse

Brilliant Mars shines atop dimmer Spica in the constellation Virgo in this photo taken Sunday night April 6. The planet now rises at sunset and is easy to spot around 9:30 p.m. in the southeastern sky. Yes, we still have almost 4 feet of snow here in Duluth, Minn. Credit: Bob King

Mars reaches opposition today, its closest approach to Earth since Dec. 2007 and the brightest we’ve seen it since 2012. What a sight it’s become. Last night, while walking our respective dogs, my daughter took one look at the gleaming pink-orange “star” in the southeastern sky and knew immediately it was Mars.

About every two years, Mars and Earth line up on the same side of the sun at opposition. Because Mars’ orbit is eccentric (less circular than Earth’s) the two planets are closer at some oppositions than others. This year’s opposition is a relatively distant one. Illustration: Bob King

While it sounds like an act of defiance, opposition refers to Mars being on exactly opposite side of the sky as the sun. The planet rises at sunset this evening and sets when the sun pops up tomorrow morning. Not only is Mars out all night long, but being opposite the sun, it’s paired up closely with Earth on the same side of the sun as shown above.


One full rotation of Mars on April 8 created by Tom Ruen. North polar cap at top.

That’s why Mars is so doggone bright – it’s close! Of course we know that’s a relative term in astronomy. Today the Red Planet is 57.7 million miles away, which sounds rather terribly far. But keep in mind that it can be up to 249 million miles away. So yes, Earth and Mars are practically neighbors … for a little while. The same orbital motions that brought them together will also move them farther apart in the coming months.

Now here’s the kicker. Because the orbits of Earth and Mars aren’t perfect circles, the two planets are actually closest on April 14, six days past opposition. That’s the same night as the total eclipse of the moon. Even better, the moon will only be a “fist” away from the planet. What a sight they’ll make – two red orbs aglow in the southern sky.

Mars outshines its neighbors Spica and Arcturus in the east and is ever so slightly brighter than magnitude -1.46 Sirius off to the southwest. The map shows the sky around 9:30 p.m. local time tonight. Stellarium

The Red Planet far outshines the nearby stars Spica and Arcturus and at magnitude -1.5 glows a hair brighter than Sirius, the brightest star in the entire sky. While similar in brightness, their colors are dramatically different. Compare the two and tell us what you think.

One side of Mars, the side turned toward the Americas during the best observing times this week, shows relatively few features. Use the map below to help you identify other dark markings as they rotate into view in the coming days and weeks. North at bottom. Credit: Mark Justice

Mars won’t appear bigger or brighter until its next opposition in May 2016 so take a look at this miniature “eye of Sauron” beaming in the south the next clear night.

If you have a telescope, use a magnification of 150x or higher to look for the planet’s very tiny north polar cap (it’s summer there and the cap has shrunk!) and other dark markings on its surface. This week, the planet’s “blank” hemisphere is presented for observers in the Americas. Be patient. The more obvious features like Mare Erythraeum, Syrtis Major and Mare Acidalium will soon rotate into view (see map below).

Complete Mars map showing many more features. Click to learn more about Mars’ upcoming opposition. Credit: Association of Lunar and Planetary Observers (A.L.P.O).

 

Seven ways to savor the upcoming total eclipse of the moon

Next Monday night April 14-15, skywatchers across much of North and South America will get to see a total eclipse of the moon. Lunar eclipses last for hours and can be safely viewed with the naked eye. This photo was taken of the June 2011 eclipse. Credit: Muhammed Mahdi Karim

It’s been too long. The moon last slipped into Earth’s shadow for North America in Dec. 2011. Next Monday night’s eclipse will end the current dry spell and make for a thrilling night out.

Map showing where next Monday night’s (April 14-15) eclipse will be visible. The western hemisphere has prime viewing seats. Credit: Fred Espenak

This eclipse is the first of four total lunar eclipses spaced about six months apart that will be visible across most of the Americas. The others occur on Oct. 8 this year, April 4, 2015 and Sept. 27, 2015. This particular sequence of four total lunar eclipses with no partials in between is called a ‘tetrad’. While we all hope for clear skies, if the weather’s uncooperative next week, you won’t have to wait long for another eclipse.


Eclipse tetrads explained

Lunar eclipses unfold slowly, lasting up to five hours. Unlike a total solar eclipse, where the sun disappears at most a few minutes, totality during a lunar eclipse can easily last more than an hour, giving you lots of time to enjoy the spectacle.

The only downside will be the late hour. Try to get some shuteye early as most of the eclipse happens after midnight in the wee hours Tuesday morning.

Because the moon’s orbit is tilted 5 degrees, the full moon normally misses the cone of shadow cast by the Earth and we see no eclipse. But several times a year, the moon’s orbit intersects Earth’s at the time of full moon and we see an eclipse. The Credit: Wikipedia

Lunar eclipses occur during full moon when the sun, Earth and moon line up in a neat row, and the moon passes into the shadow cast by our planet. You’d think eclipses would happen every full moon, but they don’t because the moon’s orbit around the Earth is tipped 5 degrees to Earth’s orbit around the sun.

The moon’s tipped orbit (red) is the reason we only get occasional eclipses at full moon. Most of the time the moon is either a little above or below the ideal alignment. Credit: Bob King

The moon spends most of the time above or below the plane of Earth’s orbit. And since Earth casts a shadow across its orbital plane, a lunar eclipse can only happen if the moon happens to be crossing that plane at the same time it’s full. That’s why eclipses are such a now and again thing.

While total solar eclipses are only visible along a narrow strip of land or ocean, a total lunar can be seen across half the globe wherever the sky is dark and the moon is up.

The moon’s past from west to east (right to left) across the dual shadow cast by Earth. The diagram shows key times (CDT) during the eclipse listed in the table below. Credit: Fred Espenak with additions by the author

Earth’s shadow is composed of two nested components – the inner umbra, where the Earth completely blocks the sun from view, and an outer penumbra, where the planet only partially blocks the sun. Because the penumbra is a mix of shadow and sunlight, it’s nowhere near as dark as the umbra.

An eclipse is divided into stages beginning with the moon’s entry into Earth’s lighter penumbral shadow. Most of us won’t notice any shading at all until about a half hour in, when the moon is deep enough inside to reveal a subtle darkening along its eastern edge. The table below lists the times for each stage of the eclipse across the four time zones:

Eclipse Events                     EDT             CDT                 MDT                PDT

Penumbra visible 1:20 a.m. 12:20 a.m. 11:20 p.m. 10:20 p.m.
Partial eclipse begins 1:58 a.m. 12:58 a.m. 11:58 p.m. 10:58 p.m.
Total eclipse begins 3:07 a.m. 2:07 a.m. 1:07 a.m. 12:07 a.m.
Mid-eclipse 3:46 a.m. 2:46 a.m. 1:46 a.m. 12:46 a.m.
Total eclipse ends 4:25 a.m. 3:25 a.m. 2:25 a.m. 1:25 a.m.
Partial eclipse ends 5:33 a.m. 4:33 a.m. 3:33 a.m. 2:33 a.m.
Penumbra visible  ——– 5:10 a.m. 4:10 a.m. 3:10 a.m.

During a total lunar eclipse (seen on Earth) an astronaut on the moon would instead see the Earth cover the sun, its atmosphere aglow with the combined light of all the sunrises and sunrises “leaking” around the rim of the planet. The light would bathe the moonscape in deep orange light. Stellarium

Partial eclipse begins when the moon treads within the dark umbra. Nibble by nibble the shadow eats away at the lunar disk. When only a sliver of the moon remains in sunlight, you’ll notice the shadowed portion glowing an eerie red or deep copper. To understand why, imagine an astronaut on the moon looking back at Earth during the eclipse.

During the next Tuesday morning’s eclipse, the moon will be just 1.5 degrees from Spica and not far from the planet Mars in the southern sky. Don’t forget to give Saturn a nod, located about two “fists” to the left of the moon. Stellarium

From her perspective, as the Earth passes in front of the sun, it’s surrounded by a glowing red-orange ring of light. Our atmosphere bends the light from all the sunrises and sunsets around the planet’s circumference into the umbra, coloring the moon red. Earth’s shadow isn’t really black after all but more a deep rusty red. Back on Earth, the moon will hang like a ghostly amber globe near the bright star Spica.

After mid-eclipse, the moon slowly exits the Earth’s shadow and performs the whole show in reverse, transitioning back to partial eclipse and finally exiting the penumbra.

Different aspects of a total lunar eclipse from start to near finish photographed in Hefei, China on Dec. 10, 2011. Credit: Reuters

You can take in the eclipse as casually as you like, but are seven cool things you might like to watch for:

#1 – When will you detect the first hint of penumbral shading? Keep an eye on the eastern (left) side of the moon for a “dented” appearance.

#2 – What color and how bright is the totally eclipsed moon? Depending upon the aerosol content of the atmosphere (greatly affected by volcanic eruptions), eclipses range from bright copper to dark brown and even black. Try rating this one on the traditional Danjon scale where “4″ is bright and “0″ is nearly invisible.

#3 – Watch for “the night within the night” phenomenon. If you thought it was dark out at the start of the eclipse, you’ll be amazed at how inky the landscape becomes during totality. As the eclipse progresses, the stars and Milky Way return to view.

#4 – With the entire moon darkened during totality, it will be relatively easy to watch it block or occult any star within its path. Many stars ranging from magnitude +8 and 12 will be occulted when viewed through small to medium telescopes. Click HERE for stars and times.

#5 – Binocular and telescope users should also look for a blue tinge to the encroaching umbral shadow as it slowly envelops the moon caused by light refracted by the upper atmosphere’s ozone layer.

#6 – Variation in the moon’s brightness. The top half will be closer to the center of the umbra and appear darker than the bottom. How obvious will this be?

#7 – Bring home a souvenir with your camera. If you have a telescope, you can hold a cellphone over the eyepiece to get great shots of the bright phases. During total eclipse, longer exposures of 1 to 10 seconds are necessary. For that you’ll need a tripod and a camera that can shoot time exposures. Telephoto lenses will pump up the moon’s size, but even a standard lens can do a great job of recording the sunset-colored moon in a landscape setting. Set your lens to its widest-open setting (f/2.8, 3.5) and expose 10-30 seconds to include the scene.

 

Watch the moon gobble up some Hyades Thursday night

The moon is shown about 15 minutes before passing in front of Delta 1 in the Hyades star cluster for Duluth, Minn. this Thursday night April 3, 2014. The green arrow shows the moon’s direction of motion. Star magnitudes are: Delta 1= 3.8, Delta 2 = 4.8 and Delta 3 = 4.3. Created with Chris Marriott’s SkyMap software

Here’s something very fun and enjoyable to see with a small telescope or even a pair of 50mm binoculars. This Thursday night across North America the crescent moon’s dark, earth-lit edge will cover up to three stars in the familiar V-shaped Hyades star cluster.

Never heard of the Hyades? Its next door neighbor is the Pleiades cluster, the one shaped like a little dipper and better known as the Seven Sisters. At just 153 light years away, the Hyades is the closest star cluster to Earth, one of the reasons it covers a nice-sized chunk of sky and is plainly visible to the naked eye. The bright orange giant Aldebaran helps to complete the cluster’s nifty V-shape, but isn’t a true member; the star simply happens to lie along the same line of sight.

Time exposure of the Hyades star cluster shows bright Aldebaran (left) and many, many stars. Although the “three Deltas” are the highlights, the moon will cover up other fainter cluster members as well. Credit: Bob King

The moon passes near the Hyades every month but only passes through the cluster for a six-year period every 18.6 years, the time it takes the moon’s orbit to precess or cycle once around the ecliptic. This last happened from 1995 to 2001. We begin a new cycle this year.

The sun’s gravity causes the moon’s orbit to slowly rotate westward once every 18.6 years. The nodes in the diagram are the two places where the moon’s tipped orbit intersects the plane of Earth’s orbit called the ecliptic. The line connecting the nodes makes a complete circle every 18.6 years. Credit: Prof. Marcia Rieke

The sun’s gravitational pull on the moon forces its orbit to slowly rotate westward. Combined with the 5-degree tilt of the lunar orbit, the moon’s track across the zodiac constellations varies continuously to the attentive observer over an 18.6 year cycle. During part of that cycle, it crosses the Hyades; during another part it swings north and misses them.

Thursday night the dark edge of the moon will cover one, two or even three bright Hyades depending where you live. Eastern and central U.S. and Canadian observers will see the moon blot out Delta 1 followed by Delta 2 for observers in the northern U.S. and Canada. The final bright star, Delta 3, slides behind the moon for much of the central and western U.S. and Canada.

Because the moon is close to the Earth compared to the planets and stars, observers in different locations see it against a slightly different background of stars. Travel north in North America, the moon slides south. Travel south and the moon’s path shifts north.

By 10 p.m. CDT, the southern edge of the moon has covered Delta 2 and will soon cover Delta 3 as seen from Duluth, Minn. Occulted stars will reappear along the moon’s bright limb, where they’re much harder to see. For Duluth, Minn. U.S. the stars will disappear within a few minutes of 9:03 p.m., 9:56 pm. and 10:35 p.m. Created with Chris Marriott’s SkyMap software

To find out which stars and when they’ll be covered for your city or region, click the links for each below:

* Delta 1
* Delta 2
* Delta 3 

When you visit these sites, select the disappearance times of the star. Note that the times are given in Greenwich or Universal Time for April 4. Subtract 4 hours for Eastern, 5 for Central, 6 for Mountain and 7 for Pacific. For example, 2 hours UT April 4 = 9 p.m. CDT April 3.

The fun in watching occultations is to see how suddenly the star disappears when it touches the edge of the moon. Were there a substantial lunar atmosphere, it would gradually fade away instead. It’s also just plain cool to see the moon move in real time as it approaches and then blinks out the star.

Some of you will be able to see one or more of the Deltas graze the edge of the moon, popping in an out of view as they’re hidden by crater walls and mountains along the lunar profile.

Good luck!

Daylight forces the hand of night as we surge toward spring

Animation showing the Earth – with tipped axis – revolving around the sun. Seasons are shown for the northern hemisphere.

It happens every mid-winter. I wake up earlier and earlier, unconsciously responding to the daylight that spills beneath the window shade as the pace of the season quickens.

We’ve been putting seconds and minutes in our sunny-day piggy bank every since the winter solstice last Dec. 21. Those deposits are now accumulating rapidly as February gives way to March. Where I live, days were as short as 8 hours 32 minutes in late December. Today that time has swelled to 10 hours 24 minutes.

As Earth revolves around the sun, its 23.5 degree-angled axis points toward, perpendicular to and away from the sun over the year to make the seasons. Credit: Tao’olunga with additions by B. King

While a half hour of extra light may not be enough to notice, 1 hour and 52 minutes is a revelation. Many of us now drive home in bright twilight at the end of a work day. This has beneficial effects like seeing more sunsets and full moon rises. We also feel more connected with the world because we can see it. Humans weren’t born to live as troglobites in dark caves. We crave sunlight as much as clear,dark nights.

I like the extra daylight for hiking and skiing. Shorter nights also mean less time for the Earth to loose heat and the temperature to dip below zero. If you’d like to see how your day/night account is coming along, check out the UNSO’s Duration of Daylight/Darkness Table.

All things warm and fuzzy (and cold and spiky) come our way because of Earth’s axial tilt. The axis remains fixed at an inclination of 23.5 degrees, but as the planet revolves about the sun during the year, the northern hemisphere tilts toward the sun in summer and away in winter. These are the extremes. In between, we have the spring and fall equinoxes, when both hemispheres are “face on” to the sun and receive equal amounts of daylight and night.

There are mini-seasons too. Mid-February is as good a time as any to call by that name. We’re moving away from winter toward spring with night on the run and daylight gaining the upper hand. A month from today, on the verge of the spring equinox, daylight will have increased an additional 1 1/2 hours to 12 hours. For a moment day and night will balance. The next moment day surpasses night and won’t relinquish its lead until after the fall equinox.

The sun’s always high in the sky at low tropical latitudes, so the seasons don’t vary much. This diagram shows the sun’s position around noon on the winter and summer solstices and equinoxes. Stellarium

Daylight length depends upon your latitude. If you took a tropical vacation this winter, you probably noticed that the sun rose around 6 a.m. and set around 6 p.m. Closer to the equator, the sun’s path is steeply inclined to the horizon every day of the year with little change in sunrise and sunset times. The sun’s always high in the sky there at the noon hour, bringing with it those consistently warmer temperatures we’re willing to pay big bucks for.

A mid-winter sun shines through an icicle formation on Lake Superior. Credit: Bob King

At mid and high latitudes, the yearly variation in sun’s position in the sky puts it high in the sky during summer and low in the sky during winter. Low means less time above the horizon, shorter daylight hours and cold temperatures.

To better understand this, consider that on the first day of spring and fall on the equator, the sun rises due east, passes directly overhead and sets due west. On the first day of summer, the sun at noon passes 23.5 degrees ( a little more than two fists held at arm’s length) north of the overhead point, while on the winter solstice it’s 23.5 degrees south of overhead. No matter the season, the sun will always shine down from a high altitude at noon.

This view shows the sun from a mid-northern latitude city like Minnepolis, Minn. Notice how the sun’s yearly elevation spread take it much closer to the horizon (wintertime) and also quite high (summertime). The scale of this map is different from the one above because it doesn’t need to include as much sky near the overhead point. Stellarium

In Minneapolis, halfway between the equator and north pole at latitude 45 degrees north, the sun is 45 degrees high at noon on the first day of spring and fall or halfway between the overhead point and southern horizon. Come the first day of summer, it’s way up there at 68.5 degrees and roasts the back of your neck, but on the winter solstice it peaks out at just 21.5 degrees high. Better protect that neck with a scarf.

The full range of the sun’s yearly motion – 23.5 degrees north to 23.5 degrees south of the celestial equator – is the same no matter where you are on Earth, but if you live far from the equator, the sun’s altitude reaches greater extremes, making the seasons more pronounced.

Lunar secrets? How to see the moon’s hidden seas tonight

The combination of the slow rocking back and forth of the moon called libration brings into view three lunar maria or “seas” that are normally hidden around the backside – Mare Humboldtianum, M. Marginis and M. Smythii. To find them, you can use the easy-to-spot Mare Crisium. Credit: Virtual Lunar Altas

If everything revolved in perfect circles and all planet and moon orbits were concentric, the solar system wouldn’t be nearly as much fun. Consider the moon. Orbiting in a circle rather than ellipse,its distance from Earth would never vary. There’d be no “super moons” or full moons at the time the moon is closest to the Earth.

Simulated views of the Moon over one month, demonstrating librations in latitude and longitude. Credit: Tom Ruen

The moon’s orbital speed would also be constant and never get out of sync with its rotation rate. Because the moon moves slower when farthest from the Earth (and faster than average when closest), we can peer around the east and west limbs of the moon for a few days each month to see craters and lunar seas that are otherwise hidden. This apparent rocking back-and-forth of the moon, called libration, exposes an extra 7.9 degrees of lunar longitude for our viewing pleasure.

Similarly, if the moon’s orbit were exactly concentric with Earth’s and the moon’s axis straight up and down, we’d never be able to peek over and under its north and south polar regions. We’re grateful that the combination of the 5.1 degree tilt of the moon’s orbit and the 1.5 degree inclination of its axis exposes an extra 6.8 degrees of latitude. As you might guess, this tippy business is called libration of latitude.

Add in 1 degree of diurnal libration caused by our changing perspective at moonrise vs. moonset, and altogether we’re able to see 59% of the moon. Pretty cool, eh?

You can see the effects of libration tonight through next week if you have a pair of 10x binoculars or small telescope.

Here’s what the moon will look like on Feb. 14 when it will be full. Because of libration, two of the three featured lunar seas have now disappeared behind the moon’s eastern edge. Credit: NASA

Three lunar seas that normally are absent or appear as little more than skinny stripes along the extreme eastern edge of the moon are in good view this evening – Mare Humboldtianum (Sea of Humboldt), Mare Marginis (the Border Sea) and Mare Smythii, a sea named in honor of 19th century British astronomer Admiral Smyth.

Watch in the coming nights as the rock n’ rollin’ moon whisks them away.

Comet ISON update Dec. 10 – Meteor shower in the offing?

One of the last spacecraft photos of Comet ISON. It was taken with NASA’s STEREO-A probe on Dec. 6, 2013. This image was compiled using 11 photos stacked atop each other to improve the comet’s visibility. Click to enlarge. Credit: NASA / Toni Scarmato

Comet ISON has left the eyes of spacecraft for the moment and now challenges amateur and professional astronomers from the ground. To date, there has been only one positive observation by an amateur astronomer in Spain and a couple “maybes”. Many have tried to see and photograph the comet’s faint remains, but none have been successful.

The sky facing east 1 1/2 to 1 3/4 hours before sunrise for mid-northern latitude skywatchers. The comet’s position is shown daily and marked every 3 days. Stars plotted to mag. 6. Guide stars are labeled: Oph = Ophiuchus, Her = Hercules, Ser = Serpens and CrB = Corona Borealis. Click for a large version. Created with Chris Marriott’s SkyMap software

Tomorrow morning, ISON climbs to 15 degrees altitude in the morning sky before the onset of twilight. That’s high enough for someone with a fast telephoto lens or fast, wide-field telescope to make a long time exposure without haze and dawn interfering. Photos taken with typical narrower fields of view through telescopes haven’t shown the faintest trace of a nucleus or condensation at the location of ISON’s core. Wide fields might still succeed.

Frame grab from solarsystemcope.com/ison shows Comet ISON (now a debris cloud) later this month when making its closest approach to Earth of 40 million miles. It’s orbit is inclined 62 degrees to the horizontal, taking it high above Earth’s plane.

I’ve been asked whether Earth will get dusted by ISON’s dusty cloud of debris as it passes our planet on the outbound leg of its journey. The answer is almost certainly “no”. There are several reasons why. First, the debris passes far above the Earth’s orbit even at its closest approach on Dec. 26, when what’s left of the comet will be nearly directly above our planet and 40 million miles away. That’s farther than Venus and even farther than Mars during its closest approaches. I’ve read catastrophic talk ISON raining hell fire on Earth. Not gonna happen. Not even meteor fire – at least from the breakup.

Second, while the debris cloud will certainly expand and enlarge, the comet leftovers will continue to travel along the same general path as ISON. They won’t suddenly veer off and make a beeline for Earth. They carry much of the original momentum and direction as the comet that created them.

Comet ISON photographed from the International Space Station on Nov. 23. You can see the twilight glow along the Earth’s limb at bottom and part of the spacecraft in the foreground. Credit: NASA

We also have to consider that as the cloud continues to expand it will rapidly thin. While it’s true a comet’s coma (not the “hard” inner nucleus) can expand to the size of the sun and tails can reach 300 million miles (500 million km) or longer, the amount of material involved spread over those distances is vanishingly small. We’ve passed through at least one comet’s tail (Halley in 1910) with no meteor shower or other ill effects to show for it.

Comets can be powder puffs though, that’s for sure. Even as long ago as January, when ISON was at Jupiter’s distance from the sun, NASA’s Swift spacecraft found it spewing dust at 112,000 lbs. a minute. While our planet’s highly unlikely to get an outbound meteor shower, we may encounter some of ISON’s inbound flotsam and jetsam come mid- January.

Illustration showing Earth encountering Comet ISON dust in mid-January 2014. Credit and copyright: Paul Wiegert

Meteor researcher Paul Wiegert of the University of Western Ontario has been using a computer to model the trajectory of dust ejected by Comet ISON and predicts that starting about January 12 and continuing for several evenings, we stand a chance of a meteor shower from material released well before perihelion.

The dust particles will strike Earth’s atmosphere at around 125,000 mph (56 km/sec), but because they’ll be so tiny, it’s unlikely we’ll actually see anything.

Illustration showing Earth passing through dual debris streams left in the path of Comet ISON in January. Credit: Paul Wiegert / NASA

“Instead of burning up in a flash of light, they will drift gently down to the Earth below,” said Wiegert. In a fascinating twist, Earth will encounter not one but two dust streams from Comet ISON. Dust released by the comet and headed in toward the sun will pepper one side of Earth, while a second stream, blown back from the comet’s former head by sunlight, will pelt the other side.

ISON dust settling into the upper atmosphere may even serve as sites for water vapor to condense and form high-altitude, blue-colored noctilucent clouds.

As we approach the potential shower date, I’ll provide additional information. A possible radiant for the shower is in the Bootes-Draco part of the sky, which in January rises in the northeast not long after midnight. Sure, we may see nothing, but wouldn’t it be cool if ISON made its final appearance as daggers of light right here so close to home?

Space station returns to evening sky – how Russia and China helped us see it

Looking down on the aurora australis or southern lights from the International Space Station from about 250 miles up. Credit: NASA

I always enjoy the return of the International Space Station (ISS) to the evening sky. It’s fun to look up and know a half dozen people 250 miles up are flying at more than 17,500 mph over my house. For many locations in the northern hemisphere it’s now easy to spot the ISS at dusk as a brilliant, pale yellow “star” moving from west to east. Most passes happen during twilight and last about 5 minutes. Times and links for looking can be found at the end of this blog.

Since the station’s orbit is tilted 51.6 degrees to the Earth’s equator, it swings over the southern tip of South America (51.6 degrees south) back up to 51.6 degrees north across Canada and northern Europe. If you live north or south of 51.6 degrees latitude, no problem. While the ISS will never pass overhead from your high latitude, you can still see it well north and south of its orbital limits because it’s 250 miles high and visible far and wide.

The Hubble Space Telescope’s lower inclination orbit means it’s only visible from lower latitudes. Skywatchers in the northern U.S. don’t get to see regular passes as they do the space station. Credit: NASA

U.S. spacecraft, like the Hubble Space Telescope, are normally launched into orbits inclined 28.5 degrees, the same as Cape Canaveral’s latitude, to take advantage of the Earth’s speed of rotation. Our planet rotates fastest at the equator and slowest at the poles. When you launch a rocket it, gets a free ride in the west to east direction courtesy of our spinning planet. If you want to send a craft into an orbit with an inclination different from the latitude it was launched, you have to burn more fuel. That costs money.

The ISS overflies much of the civilized world from its highly-inclined orbit (shown in blue). The three curves show the ground tracks of multiple orbits around the Earth. As the ISS circles the planet, Earth rotates to the east, shifting each new track to the west.

So why not save money by sending the ISS into an orbit equal to Cape Canaveral’s latitude? Sure, but we’re not the only ones running the space station operation. Russia shuttles astronauts and cargo to and from the space station with its Progress and Soyuz spacecraft. The U.S. worked with Russia to pick the best orbital tilt. Since Russia launches Progress and Soyuz from Baikonur (latitude 46 degrees N), a high inclination orbit made economic sense. It also lets astronauts study more of the Earth’s surface compared to an orbit closer to the equator. 75 percent of the planet and 95 percent of its inhabited lands are open to view.

Rockets coming from the Cosmodrome in Baikonur, Russia headed for the space station are sent into orbits inclined 51.6 degrees to avoid overflying China shortly after launch. Credit: Wikipedia

OK great. So why isn’t the orbit inclined 46 degrees?  Baikonur’s not too far from the Chinese border as the rocket flies. Any booster stages falling back to Earth after launch would land in China, not the most desirable situation. Launching at the steeper trajectory of 51.6 ensures the boosters remain in Russian with the spacecraft well on its way into space when it passes over China.

With its lower inclination orbit of 28.5 degrees, the Hubble Space Telescope can’t be seen from the northern U.S. and Canada. Had we not cooperated with the Russians on ISS missions, it’s possible that the space station would have been launched into a 28.5 degree orbit and been invisible to skywatchers across large stretches of the globe. Including my town of Duluth!

I’d like to tell you what the astronauts are up to this week, but the government shutdown has shuttered most NASA websites including those connected with the space station and its status. Strangely enough, NASA’s Spotthestation site, which will e-mail you with predictions of where and when to see the ISS, is still up and running.

Below I’ve included times when the station is visible from the Duluth, Minn. region. You can always get predictions for your town from Spaceweather’s Satellite Flyby page or times and handy maps from Heavens Above.

All times CDT:

* Tonight Oct. 10 beginning at 7:30 p.m. Maximum height: 32 degrees. Appears in the south and disappears in the east.
* Fri. Oct. 11 at 8:18 p.m. Max. height: 76 degrees. Appears in the west and disappears nearly overhead
* Sat. Oct. 12 at 8:19 p.m. Max. height: 44 degrees. Appears in the west and disappears in the north.
* Sun. Oct. 14 at 7:31 p.m. Max. height: 57 degrees. Appears in the west and disappears in the northeast

Weekend “Black Hole” full Moon brightest and closest of the year

Watch for a bigger and brighter full moon than usual tomorrow and Sunday nights. Photo illustration: Bob King

Wishing you a grand first day of summer today and clear nights ahead. This weekend we’ll see the full moon dangling like heavy fruit low in the southern sky. If it looks a tad bigger than last month’s Full Flower Moon, it really is. The moon reaches perigee – closest point to Earth in its orbit – at 6:11 a.m. CDT Sunday morning June 23 just a half hour before the moment of full moon. At the same time it will hover in front of the Milky Way’s central supermassive black hole.

With all those superlatives, you might think I’m setting you up for the end of the world. Trust me, I’m not. The full moon is near the same spot every June and perigees are almost as common as dandelions.

Like the planets do around the sun, the moon moves in an elliptical orbit around the Earth. Once a month it’s closest to us at perigee and farthest away at apogee. Next apogee will be at new moon on July 7. The moon’s average distance from Earth is 238,856 miles (384403 km).

The moon follows an elliptical path around the Earth with one side of its orbit some 31,000 miles (50,000 km) closer (perigee) to our planet than the other side (apogee). Since the moon orbits the Earth every 27 days it reaches perigee once or sometimes twice a month.

So what makes this one special? Well, not all perigees are alike. Some are closer than others and occur at times other than full moon. The closest perigees, like this Sunday’s, occur when the moon is either full or new – times when Earth, moon and sun are all lined up in a row. The sun’s gravity tugs more strongly on the moon at these phases, stretching its orbit and leading to extreme values for perigee and apogee.

No one notices an unusually large first quarter or crescent moon, but we all sit up and pay attention to a bigger-than-normal full moon.

The difference between the the moon at its most distant apogee and closest perigee dramatically illustrated in this pair of photos taken in 2006. The full moon can be as much as 14% bigger and 30% brighter when closest. The weekend’s moon will be 12% bigger than January 2014′s apogee full moon. Credit: Anthony Ayiomamitis

The moon’s most distant perigee (230,000 miles) happened at last quarter phase on March 5 this year. Sunday’s will be the closest of the year at just 222,000 miles (357,000 km). Some keen-eyed skywatchers might notice the moon looking a little larger than it will at apogee on Jan 14, 2014. I say might. Without a reference, it’s terribly hard to compare sizes. The moon illusion, an apparent bloating of our satellite when seen low in the sky, further complicates the view. Still, facts are facts. The moon will be bigger and brighter this weekend than on any other night this year.

Saturday night’s full “Black Hole Moon” will lie about one fist held at arm’s length left and above the center of Milky Way galaxy.  Astronomers call the spot Sagittarius A* (Sagittarius A star). Blocked by intervening dust and invisible to optical telescopes, it marks the site of a supermassive black hole. Created with Stellarium

Not only does the closest perigee of the year coincide with Full Moon, but the moon will be in the “Teapot” constellation Sagittarius in approximately the same direction as our galaxy’s 4-million-mass black hole. Look toward the moon and you can imagine it there munching its way on gas clouds and stars that pass that pass too close for comfort. Given that the beast is 26,000 light years (156 quadrillion miles) from us, neither moon nor monster have any gravitational inkling of the other.

Since full phase happens early Sunday morning, the moon will appear full to the eye both Saturday and Sunday nights. I hope you’ll get to enjoy the show.

Space station marathon week – an excuse to stay up all night

Time exposure of the International Space Station during a pass across the northern sky. The ISS looks like a brilliant, pale yellow star that moves from west to east. A typical pass takes about 5 minutes. Photo: Bob King

Every early June in the northern hemisphere (December in the southern), the International Space Station (ISS) can be observed on multiple passes from dusk till dawn. Taking only 90 minute to circle Earth, the station is normally visible once or twice a night during twilight, when it catches the sun’s rays 250 miles up and glimmers brightly against a darkening sky.

Passes continue through the night – yep, it’s up there – but we can’t see the football field-sized satellite because it’s in Earth’s shadow. The sun has set for the astronauts; they look out the window and admire the sparkling lights of cities below and stars above.


Video of sunrise and (almost) sunset seen from the space station around summer solstice.

That all changes for a week or two around the summer solstice thanks to our planet’s tilted axis and the highly inclined orbit of the ISS. The space station’s orbit is tipped up at an angle of 51.6 degrees to the Earth’s equator. That means it visible anywhere on the ground between 52 degrees north and south of the equator – a vast region that includes 90% of humanity.

During northern hemisphere summer, Earth’s north pole is tilted 23.5 degrees toward the sun. When combined with the space station’s steep orbital tilt, the ISS manages to avoid Earth’s shadow, remaining in constant sunlight during its entire orbit. For a daydreaming astronaut staring out the cupola windows, the sun never sets. He watches it drop to edge of the globe and then rise right back up again. Watch the video above and you’ll see what I mean.

In the diagram, the circle represents Earth with its north pole tipped sunward around the time of summer solstice. The ISS’s orbit – tipped well up from the equator – is shown in profile. Notice how close the station passes to the day-night line or terminator. This allows it to remain in sunlight its entire orbit. Illustration: Bob King

The diagram will help you picture what’s going on. Earth’s axis points off to the left with the northern hemisphere tilted toward the sun. The terminator is the boundary between day and night on the planet, and the equator cuts perpendicular to the axis. The space station’s tipped orbit places it very near the terminator this time of year, high enough for it to catch the sun’s rays all night long.

For sky watchers that means that virtually every time the station comes over your house this time of year, you’ll see it shining in sunlight even in the middle of the night. Depending on your particular location, five passes a night are possible. Amazing!


Half-minute video of the space station tracked through a telescope

So break out the Cheetos and tea and see how many times you can spot the station in the week ahead. I also encourage anyone with a telescope to try pointing it at the ISS during one of its frequent passes. A magnification of 50x will easily show at least two orange solar arrays sticking out on either side of a shiny, white blob (the space station proper).

Give it a try – you won’t believe it. It’s almost like seeing Saturn for the first time in a telescope. The best way to grab this fast-moving object is to aim the scope a short distance ahead of where you expect the ISS to travel and dart back to the eyepiece asap. You may miss on the first try, but eventually you’ll snag it. Move the telescope to match its motion and study the image for fascinating details. The best views are when the ISS passes nearly overhead. That’s when it’s closest to you and appears largest.

I saw the panels last night during a 2:12 a.m. pass and am looking forward to at least a half-marathon tonight. I’d do the full marathon but hey, I have to work tomorrow.

The ISS orbits about 250 miles above Earth about 18 times a day at an average speed of 17,000 mph (27,000 km). Credit: NASA

For viewing times for your city, log in to Heavens Above or check out Spaceweather’s Satellite Flybys. The former provides great maps showing the satellite’s path. You can also sign up at Spot the Station and have NASA e-mail you anytime there’s a good pass for your location. Be aware however that they only send alerts for the better passes; marginal but still visible ones are not given.

Below are times when the ISS will be visible from the Duluth, Minn. region:

*  Tonight June 2-3 starting at 11:49 p.m. First pass high in the eastern sky starting at 11:49 p.m. Watch for the station to first appear high overhead and move east. Second pass at 1:23 a.m. across the north. Third pass at 3 a.m. across the north.

* June 3-4 – Banner night! First pass at 10:58 p.m. across the south-southeast. Second  at 12:34 a.m. in the northern sky. Third at 2:11 a.m. in the north. Fourth at 3:48 a.m. straight across the top of the sky.

* June 4-5 – Ultimate Marathon Night! First pass at 10:09 p.m. across the southeast. Second at 11:45 p.m. high in the northern sky. Third at 1:22 a.m. in the north. Fourth at 2:59 a.m. in the north. Fifth at 4:36 a.m. in bright twilight in the southwestern sky.

In darkness the moon is reborn

If we could see the moon today, it would be a very thin crescent only a few degrees from the sun. Tomorrow it’s in new moon phase. Maps created with Stellarium

What’s old today but instantly becomes young again tomorrow? If you guessed the moon, you’re right! Today the moon winds up its current cycle of phases as an exceedingly thin crescent so close to the sun it’s invisible in the solar glare.

The moon’s cycle has always been a metaphor for life. Every month it’s born again as a thin crescent in the western evening sky, grows to a half-pie seven days later and reaches its full power and radiance when full at 14 days. After full, the moon’s radiance declines as its phase wanes to last quarter (21 days) and then to a whiskery crescent at dawn. Before it finally disappears in the sun’s glare, the moon, now 28 days old, reaches the end of its “life” cycle. But only briefly. The very next day, moments after new moon phase, it’s reborn again as an evening crescent.

When we run into troubles in our lives, we might look to the ever-renewing moon for inspiration.

The sky looking west-southwest a half hour after sunset Monday evening Feb. 11, 2013. You might be able to spot dimmer Mars in binoculars.

Tomorrow morning at 2:20 a.m. (CST) the moon will be exactly lined up with the sun and pass through new moon phase. Skywatchers in the western hemisphere won’t see the moon either day because it’s in the same direction as the sun and swamped by glare.

By Monday Feb. 11 however, the moon’s orbital motion will remove it far enough from the sun to be visible during evening twilight.  And there’s a bonus. The crescent will float a few degrees above the planet Mercury.

I’ve removed the atmosphere in this illustration so you can see where the moon is today at noon (CST), tomorrow morning when it reaches new moon phase and tomorrow Feb. 10 at noon. It passes north of the sun, which is in the constellation Capricornus. Notice all the planets in the neighborhood.

If we were to follow the moon today through new moon and into tomorrow, we’d notice it passes well north of the sun. Most of the time, the new moon is either north or south of the sun because its orbit is tipped about 5 degrees relative to Earth’s orbit.

The moon’s tilted orbit causes it to swing north or south (pictured here) of the sun from Earth’s perspective. A couple times a year however it crosses directly in front and a total solar eclipse is visible from somewhere on Earth. Illustration: Bob King

Over the course of its monthly cycle, it bobs up and then down along its tilted orbit. But 2 or 3 times a year, when the moon intersects the plane of Earth’s orbit at the same time as new moon phase, it crosses directly in front of the sun and we see a total solar eclipse. In fact, this is the only time we can see a new moon with the naked eye. It looks exactly like what you’d expect – a blank, black disk scrubbed free of its past life, waiting to begin the next as a tender crescent.

The new moon – black disk – is plainly visible silhouetting the sun during a total solar eclipse. Credit: Luc Viatour