The Ellensburg, WA sky for the week of February 27, 2021

Saturday: From lower left to upper right, Jupiter, Mercury, and Saturn are just above the east-southeastern horizon at 6:00 a.m. Saturn is the highest of the three but also the dimmest.

Sunday: Even though Zubenelgenubi is the second brightest star in Libra, its name means Southern Claw in Arabic, an artifact of the time that it was considered part of Scorpius the scorpion. Zubenelgenubi is a visual binary, consisting of a white and yellow star that are about arc minutes apart from each other in the sky. This is about the same angular diameter of a medium sized dark spot, or mare, on the Moon and can be observed with the naked eye under good sky conditions. In actuality, they are at least 5,500 astronomical units apart from each other, about 130 times the distance between the Sun and Pluto. Zubenelgenubi is two fists above the south-southwestern horizon at 6:00 a.m.

Monday: The bright star Spica finally makes an appearance in the evening sky. It is one fist above the east-southeastern horizon at 11:00 p.m.

Tuesday: Do you see a hunter when you look at Orion, due south at 7:30 p.m.? The bright reddish star Betelgeuse, five fists above due south, and Bellatrix, the bright bluish-white star one fist to the right of Betelgeuse, are the broad shoulders of the hunter. The bright bluish-white star Rigel and Saiph, the bright star to the left of Rigel, represent the knees.  The Maya saw the equilateral triangle formed by Rigel, Saiph, and the left-most belt star as the “Three Stones of the Hearth”. The Orion Nebula is in the center of the hearth and it represents the flame, called K’ak.

Wednesday: Venus is right next to the Sun in the sky for the next two months, making it nearly impossible to see with the naked eye either day or night. But that wasn’t the case on March 4, 1865. On the day of Abraham Lincoln’s inauguration, many attendees reported seeing Venus in the daytime sky. Venus is always bright enough to be seen in a clear daytime sky. You just need to know where to look. And Honest Abe’s fans knew where to look. Read more about this at https://spacewatchtower.blogspot.com/2021/01/venus-surprises-in-day-time-sky-shortly.html.

Thursday: The asteroid Vesta will be in opposition tonight. That doesn’t mean that Vesta refuses to eat its vegetables. Opposition means that Vesta is on the opposite side of the Earth as the Sun. When an object is in opposition, it is at its highest point in the sky during the darkest time of the day. Thus, opposition is typically the best time to observe an asteroid. Vesta is about five and a half fists above the southeast horizon at 11 p.m. You’ll need binoculars to see it. First find the moderately bright star Denebola, which is five fists above due southeast. Once Denebola is in your field of view, move your binoculars up and to the right until you get to the next brightest star in the region. Vesta is to the left of this star. Over the next few nights, Vesta can be seen moving up away from this star. Vesta is the brightest asteroid and the third largest. It was visited by NASA’s Dawn mission in 2011 and 2012.

Friday: CWU encourages physical distancing. But astronomy learning lives on! The Physics Department is hosting a First Saturday VIRTUAL planetarium show tomorrow from noon to 1:00 p.m. CWU physics graduate and Teach STEM student Jessica Kisner will give a show called “Astrobiology and the Search for Life”. The show will feature what we know about the possibility for life elsewhere in the universe? There is a virtual planetarium show on the first Saturday of nearly every month of the school year. Register at https://rebrand.ly/Mar2021FirstSaturday.

The positional information in this column about stars and planets is typically accurate for the entire week. For up to date information about the night sky, go to https://nightsky.jpl.nasa.gov/planner.cfm. 

The Ellensburg, WA sky for the week of February 20, 2021

Saturday: Tonight is a great night to look for the Big Dipper. Tomorrow will be a great night to look for the Big Dipper. In fact, every night for many centuries will be great nights to look for the Big Dipper. But the Big Dipper’s shape slowly changes over many, many, many, many centuries. (Have I reached my word count yet?) Tens of thousands of years ago, it didn’t look like a dipper and tens of thousands of years from now, it will no longer look like a dipper. For a short video simulation of the changing Big Dipper, go to https://youtu.be/txJH8RlIoXQ. For a look at the current Dipper, face northeast at 8:00 p.m. The lowest star, Alkaid, is two fists held upright and at arm's length above the horizon. 

Sunday: It’s getting dark. The last remnant of twilight has disappeared. Suddenly, you notice a large softly radiant pyramid of light in the western sky. The base of this ghostly triangle is along the west horizon and the peak stretches two or three fists above the horizon. It is not really a ghost. It is an effect called the zodiacal light. This light comes from sunlight reflecting off dust grains in our solar system. The effect is the most visible when the band of constellations called the zodiac makes a steep angle with the horizon. You need a clear dark sky with no haze or light pollution to see the zodiacal light. At its brightest, the zodiacal light rivals the light of the central Milky Way. Look for the ghostly patch after twilight for the next few weeks.

Monday: Mars is five and a half fists above due southwest at 7:00 p.m.

Tuesday: Mercury and Saturn are just above the east-southeastern horizon at 6:15 a.m. Mercury is the slightly brighter of the two and to the left of Saturn.

Wednesday: On these late winter mornings, it is still difficult to get going. You just want to plop into a chair and sit still. But, are you really sitting still? You’re moving at about 700 miles per hour due to the rotation of the Earth on its axis and 66,000 miles per hour due to the revolution of the Earth around the Sun. If that’s not enough, the entire solar system is orbiting the center of the galaxy at a whopping 480,000 miles per hour! So while you may be sitting still with respect to your living room (and all of the overachievers in your house), you are NOT sitting still with respect to the center of the galaxy. For more information about this concept, go to https://nightsky.jpl.nasa.gov/docs/HowFast.pdf. 

Thursday: Are you lonesome tonight? Alphard in the constellation Hydra is. Also spelled Al Fard, Arabic for “the solitary one”, Alphard is in a region of the sky without any bright stars. Alphard really ought to have a lot of friends. It is an orange giant star like better known stars such as Arcturus and Aldebaran. It pulsates, making it interesting to astro-seismologists. And it is on the flag of Brazil. There’s no reason for it to be lonely. Go introduce yourself to Alphard, three and a half fists above due south at 11:00 p.m.

Friday: Two bright stars, Vega and Deneb, are hugging the northern horizon together at 11:00 p.m. Vega, the brighter of the two, is about a half a fist above the northeastern horizon. Supergiant Deneb to two and a half fists to the left of Vega, closer to due north.

The positional information in this column about stars and planets is typically accurate for the entire week. For up to date information about the night sky, go to https://nightsky.jpl.nasa.gov/planner.cfm.

The Ellensburg, WA sky for the week of February 13, 2021

Saturday: On February 18, 1930, Clyde Tombaugh discovered Pluto, at that time classified as the ninth planet. However, as astronomers started discovering a lot of similar objects in that part of the Solar System, they realized that they had a classification crisis on their hands. Should everything in this region of the Solar System be named a planet? Eventually the International Astronomical Union (IAU) reclassified Pluto and all future Pluto-like objects as dwarf planets. This week you can celebrate the discovery with the people at Lowell Observatory, the “home” of Pluto’s discovery. Go to https://iheartpluto.org/ for more information about nightly events from tonight through February 18.

Sunday: The sky is so wondrous. It makes me want to sing. Who can forget that memorable song by Three Dog Constellations Night, “The sky is black. The stars are white. Together we learn to find the light.” Well, maybe it didn’t go like that. Which is good. Because not all stars are white. Most stars are too dim to notice a color. But, two of the stars in the constellation Orion provide a noticeable contrast with each other. Betelgeuse, five fists held upright and at arm’s length above the southern horizon at 8:00 p.m. is a red giant. Rigel, the bright star about two fists to the lower right of Betelgeuse, is a blue giant.

By the way, the three dog constellations are Canis Major, the greater dog, found one and a half fists to the lower left of Orion; Canis Minor, the lesser dog, found two and a half fists to the left of Betelgeuse; and Canes Venatici, the hunting dogs, found low in the northeast sky, halfway between the Big Dipper and the horizon. Canis Major contains Sirius, the brightest star in the nighttime sky.

Monday: This President’s Day, let’s remember Abraham Lincoln: 16th president, country lawyer, man on the penny, wrestler, and astronomer. Astronomer? Well, maybe not an astronomer, but someone who used observational evidence from the sky to solve a problem. In 1858, Lincoln defended Duff Armstrong, a family friend who was accused of murder. The prosecution thought they had a strong case because their primary witnesses claimed to have observed the killing by the light of the nearly full moon. Let’s listen in on the trial courtesy of the 1939 film, Young Mr. Lincoln.

Lincoln: How’d you see so well?

Witness: I told you it was Moon bright, Mr. Lincoln.

Lincoln: Moon bright.

Witness: Yes.

(Dramatic pause as Lincoln reaches for something)

Lincoln: Look at this. Go on, look at it. It’s the Farmer’s Almanack (sic). You see what it says about the Moon. That the Moon… set at 10: 21, 40 minutes before the killing took place. So you see it couldn’t have been Moon bright, could it?

Lincoln used the known information about Moon rising and setting times for August 29, 1858 as evidence in a trial. This is one of the earliest uses of forensic astronomy. For more information about Lincoln’s “almanac trial”, go to http://goo.gl/r83q4X. 

Tuesday: The bright star Regulus is one and a half fists above due east at 7:00 p.m.

Wednesday: Saturn is just above the east-southeastern horizon at 6:30 a.m.

Thursday: After traveling more than 450 million kilometers, Mars Perseverance rover and Ingenuity helicopter lands in Jezero Crater today. Astronomers think that Jezero Crater was filled with water a few billion years ago so Perseverance will be looking for signs of past life. Read more about the mission at http://tiny.cc/gh4jtz, including instructions on where to watch it live. Mars is five and a half fists above due southwest at 7:00 p.m., just a half a fist to the upper right of the Moon.

Friday: Clyde Tombaugh discovered the first planet 9. Will you discover the new Planet 9? You and thousands of others will have the opportunity to comb through images of the sky from NASA’s Wide-field Infrared Survey Explorer (WISE). You’ll view short “flipbook” movies of the same patch of sky on different nights. Any point of light that moves could be Planet 9 or another undiscovered Solar System object. Read about how you can join the search for Planet 9 at http://tiny.cc/fh4jtz. 

 
The positional information in this column about stars and planets is typically accurate for the entire week. For up to date information about the night sky, go to https://nightsky.jpl.nasa.gov/planner.cfm.

The Ellensburg, WA sky for the week of February 6, 2021

Today:  CWU encourages physical distancing. But astronomy learning lives on! The Physics Department is hosting a First Saturday VIRTUAL planetarium show today from noon to 1:00 p.m. Former CWU and current Green River College professor Tony Smith will give a show called “Love in the Sky”. The show will feature love stories as told through celestial mythologies. Hmm. Why would the February show be about love? There is a virtual planetarium show on the first Saturday of nearly every month of the school year. Register at https://rebrand.ly/Feb2021FirstSaturday. 

Sunday: Are you going to watch the super bowl tonight? Is the bowl really that super? After all, half the night the bowl is tipped upside down, spilling out all of its contents. But don’t just focus on the functionality of the bowl. Think about how it inspires people all across the world to look at the night sky. In Mongolia, participants in the super bowl are known as gods. An Arabian story says the super bowl is a coffin. I encourage you to go outside tonight at about 8:00 p.m., after whatever unimportant thing you have been doing since 3:30 p.m. Look low in the north-northwestern sky and watch the super bowl, also known as the Big Dipper, balancing on the end of its handle, proudly displaying its large bowl. 

Monday: Mars is five fists above the southwestern horizon at 8:00 p.m. Iceland is 1,400 km above Great Britain at all times. What do they have in common? NASA is testing the next-generation Mars mission in an Icelandic lava field. The Rover-Aerial Vehicle Exploration Network, or RAVEN, pairs an autonomous rover with remote-controlled drones. The mission will explore a part of Mars that is similar to the terrain in Iceland. For more information about RAVEN and the use of drones in science, go to https://www.atlasobscura.com/articles/iceland-mars-drone-exploration. The article also includes many quotes from geologist, drone advocate, and Central Washington University graduate Angie Diefenbach.

Tuesday: The good news is the days are getting longer and the nights are getting shorter. The better news for most readers of this column is the farther north you go in the United States, the longer the days get. Here in Ellensburg, there is almost one and a half more hours of daylight than on the first day of winter. In the southern part of the US, there is only 40 more minutes of sunlight. If you’d like to have your own fun with day lengths and other time questions, go to https://www.timeanddate.com/sun/.

Wednesday: The bright star Arturus is one and a half fists above the eastern horizon at 11:00 p.m.

Thursday: The moon is almost directly between the Earth and the Sun today. That means you won’t be able to see it. But that does not mean it doesn’t exist. Contrary to the belief of toddlers and immature politicians, just because you can’t see something doesn’t mean it doesn’t exist. (Note a double negative statement followed by a triple negative statement. I’m not unsorry about that.) Now, back to the science. What would happen to the earth if the moon really didn’t exist? In that 2013 blockbuster Oblivion, aliens destroy the moon and Tom Cruise survives. But the long-term effects on the earth would be devastating to life as we know it. The moon stabilizes the spin axis of the earth keeping the seasons fairly uniform over time. For more information on what would happen to the earth if the moon were destroyed, go tohttps://www.popsci.com/what-would-happen-if-moon-suddenly-disappeared/. For more information on Thomas Cruise Mapother IV, go to http://en.wikipedia.org/wiki/Tom_Cruise. 

Friday: Your first Friday morning challenge: eat a healthy breakfast. Your second challenge: find Saturn just above the east-southeastern horizon at 6:45 a.m.

The positional information in this column about stars and planets is typically accurate for the entire week. For up to date information about the night sky, go to https://nightsky.jpl.nasa.gov/planner.cfm. 

The Ellensburg, WA sky for the week of January 30, 2021

Saturday: Are you interested in participating in astronomy research? You don’t need to go back to school. You don’t need to spend thousands of dollars getting a fake degree from an online university. The scientists working on the High Resolution Imaging Science Experiment, or HiRISE, camera on NASA's Mars Reconnaissance Orbiter would like your input on which objects they should target for close-up pictures. While you may think the scientists are just trying to build interest in their project by having people look at pretty pictures, there is a real scientific benefit to having many eyes searching for interesting targets. There aren’t enough scientists to carefully inspect all of the low power images. And surprisingly, computers are not nearly as effective as people in making nuanced judgments of images. So, go to https://www.uahirise.org/ and click on the HiWish button. You’ll be on your way to suggesting close-up targets for NASA's Mars Reconnaissance Orbiter. If that is too much work for you, just go outside. Mars is nearly six fists held upright and at arm’s length above the southwest horizon at 7:00 p.m.

Sunday: At 6:00 p.m., Mercury is less than a fist above the west-southwest horizon. 

Monday: Goodnight room. Goodnight mini-moon. Goodnight cow jumping over the Moon. This past November, Earth captured a mini-moon, a 1960s-era rocket. But tonight, it makes one last close pass, a chance to say “goodbye mini-moon” before it escapes Earth’s gravitational pull and no longer orbits Earth. For more on how you can see the mini-moon online today, go to https://earthsky.org/space/2020-so-mini-moon-asteroid-or-space-junk. 

Tuesday: Today is Groundhog Day, an important day for pop culture astronomers and Bill Murray movie fans. If Punxsutawney Phil doesn’t see his shadow tomorrow morning, he is telling us that he follows the Chinese calendar and that spring starts early. On the Chinese calendar, equinoxes and solstices occur in the middle of their respective seasons. In order for the vernal equinox to occur in the middle of spring, spring must start on February 3 or 4, depending on the year. Thus, if Phil doesn’t see his shadow, legend is that spring will start on February 3 or 4 as on the Chinese calendar. If Phil sees his shadow, he is telling us he agrees with the western calendar and that there will be six more weeks of winter meaning spring will start near March 20.

Wednesday: If you want to look at the ten brightest objects in the Solar System as seen from Earth, start with the asteroid Vesta at number 10. It is the second largest and brightest asteroid. You can’t see it with the naked eye but it is easy to see using binoculars. At 10:00 p.m., find the bright star Denebola, one fist above the eastern horizon, at the tail end of Leo the lion. Put Denebola at the left side of your binocular field of view. Vesta will be near the middle, just above a little triangle of stars. Watch it over the next few days as it moves upward in the field of view

Thursday: Winter is a good time to see the thick band of the Milky Way galaxy. It arches high in the early evening sky at 8:00 p.m. starting in the southeast by Sirius, the brightest star in the night sky. Climbing from Sirius through the "horns" of Taurus to the bright star Capella nearly straight overhead, it drops down toward M-shaped Cassiopeia in the north and the tail of Cygnus the swan and its bright star Deneb, in the northwest. 

Friday: CWU encourages physical distancing. But astronomy learning lives on! The Physics Department is hosting a First Saturday VIRTUAL planetarium show tomorrow from noon to 1:00 p.m. Former CWU and current Green River College professor Tony Smith will give a show called “Love in the Sky”. The show will feature love stories as told through celestial mythologies. Hmm. Why would the February show be about love? There is a virtual planetarium show on the first Saturday of nearly every month of the school year. Register at https://rebrand.ly/Feb2021FirstSaturday.

The positional information in this column about stars and planets is typically accurate for the entire week. For up to date information about the night sky, go to https://nightsky.jpl.nasa.gov/planner.cfm.

Thje Ellensburg, WA sky for the week of January 23, 2021

Saturday: Winter is the best season for finding bright stars. And if you only want to set aside a few minutes, 10 p.m. tonight just might be the best time because the winter hexagon is due south. Starting at the bottom, find Sirius, the brightest star in the night sky, two and a half fists held upright and at arm’s length above the southern horizon. Going clockwise, Procyon (6th brightest star visible from Washington state) is about two and a half fists to the upper left of Sirius. Pollux (12th brightest) is about two and a half fists above Procyon. Capella (4th brightest) is about two and a half fists to the upper right of Procyon and close to straight overhead. Going back to Sirius at the bottom, Rigel (5th brightest) is about two and a half fists to the upper right of Sirius. Aldebaran (9th brightest) is about three fists above Rigel. Adhara (16th brightest) is a little more than a fist below Sirius and Castor (17th brightest) is right above Pollux. Betelgeuse (21st brightest) is in the center of the hexagon. That’s nine of the 21 brightest stars visible in the northern United States in one part of the sky. This list used to be nine of the 17 brightest. But Betelgeuse has dimmed from the 7th to the 21st brightest star in the sky. For more information about this dimming, go to https://youtu.be/FosDJOVaKFc. 

Sunday: Venus is poking up above the southeastern horizon at about 7:10 a.m., just before sunrise. Soon it will be lost in the glare of the Sun.

Monday: Mars is five and a half fists above the south-southwest horizon at 7:00 p.m.

Tuesday: Lately the Sun has been boring. Well, except for the life-giving energy it radiates towards Earth. And the gravity that keeps us from drifting into the abyss. But there have not been very many sunspots. In fact, the recent minimum was one of the weakest in years. Many solar astronomers think the upcoming solar cycle will be weak as well. But the National Center for Atmospheric Research begs to differ. They have analyzed longer term fluctuations in the cycle and are predicting one of the strongest solar cycles in decades. Read more about the sunspot debate at https://earthsky.org/space/sunspot-cycle-25-among-strongest-on-record-says-ncar.

Wednesday: Tonight’s Full Moon is called the Full Wolf Moon since wolves tend to howl more often on the cold winter nights.

Thursday: Do you ever take photos to spy on your neighbors? The Hubble Space Telescope does. Last week, Hubble scientists released the best ever image of the Triangulum Galaxy, the second closest spiral galaxy to Earth. Hubble’s Advanced Camera for Surveys weaved together 54 separate images to provide enough detail to see 10 million individual stars out of the estimated 40 billion stars in the galaxy. See the pictures at https://www.spacetelescope.org/news/heic1901/. At 7:00 p.m., the Triangulum Galaxy is six and a half fists above the southwestern horizon and two and a half fists to the upper right of Mars. The galaxy is visible with binoculars. First find Mars. Then move your binoculars to the upper right until you see two stars of similar brightness to each other, one at the top and the other at the bottom of your field of view. Continue to move your binoculars the same distance to the upper right and you will be pointing at the Triangulum Galaxy, also known as Messier 33 (M 33). If you reach a third star about the same brightness as the first two, you have moved too far.

Friday: At 10:30 p.m., the blue giant star called Adhara is one and a half fists above due south. It is the 22nd brightest star in the sky. Currently over 430 light years away, Adhara was only 34 light years away five million years ago. That proximity made it the brightest star in the nighttime sky at the time.

The positional information in this column about stars and planets is typically accurate for the entire week. For up to date information about the night sky, go to https://nightsky.jpl.nasa.gov/planner.cfm.

The Ellensburg, WA sky for the week of January 16, 2021

Saturday: How do you study the life cycle of a dog? Easy. Get a dog from the animal shelter, care for it for 15 years and study it. How do you study the life cycle of a star? Easy. Pick a star, watch it for a few billion years, and…. Wait a minute. Astronomers can’t observe something for a few billion years. Instead, they study stars that are at different points in their long life cycle and piece together the information from those different stars. What they do is like studying a one-year-old dog for a few minutes, then studying a different two-year-old dog for a few minutes, and so on. The sky in and near the constellation Orion provides an example of four objects at different points of star life.

First, find Rigel, the bright star in the lower right corner of the constellation Orion. This star, about 15 times the mass of the Sun, is rapidly burning its fuel for a high energy but short-lived existence, is exactly three and a half fists held upright and at arm’s length above due south at 9:30 p.m. About one fist up and to the left are the three objects of Orion’s sword holder. The middle “star” is really a star-forming region called the Orion nebula. It is illuminated by four baby stars each about 15 times the mass of the Sun. Betelgeuse, in the upper left corner of Orion, is a star at the end of its life. It started out life about 15 times the mass of the Sun. Finally, look about two fists to the right and one fist down from Rigel. You will be looking at a star that is about one tenth as bright as Rigel but still the brightest in its local region. The third star to the right of that star is called Epsilon Eridani, the most Sun-like close and bright star. 

Sunday: Tonight in Ellensburg, WA, the Sun sets at 4:44 p.m. Saturn sets at 5:10 p.m. and Jupiter sets at 5:26 p.m., making them a challenge to spot with the naked eye. Use binoculars and scan up from the horizon right after the Sun sets. DO NOT look at the Sun with binoculars or your naked eyes. Mercury will be easier to spot because it is still a half a fist above the southwestern horizon at 5:30, when the sky is getting dark.

Monday: Let’s review three important sets of three cats. There’s Josie, Valerie, and Melody of Josie and the Pussycats. Felix, Tom, and Sylvester from old time cartoons. And, if you want to get away from the mind-numbing effects of television, there’s Leo the lion, Leo Minor, and Lynx in the night sky. Leo is by far the most prominent of these three constellations. Its brightest star called Regulus is two and a half fists above the east-southeastern horizon at 10:00 p.m.. The backwards question mark-shaped head of Leo is above Regulus and the trapezoid-shaped body is to the left of it. Leo Minor consists of a few dim stars right above Leo. Pretty wimpy. The long dim constellation called Lynx spans from just above Leo Minor to nearly straight overhead. You and fellow stargazers won’t need to wear a long tail or ears for hats to enjoy these stellar cats.

Tuesday: In 1984, American singer Rockwell released the song “Somebody’s Watching Me”, backed up by Michael Jackson. In 2020, NASA’s Spitzer Space Telescope released a picture of two bubbles of gas and dust that look like eyes watching you. Stare back at them by going to http://tiny.cc/n248tz. 

Wednesday: Mars is less than one fist above the Moon in the southwestern sky at 8:00 p.m. Uranus is the brightest object just to the lower left of Mars in a binocular field of view.

Thursday: You never see a giraffe on the ground in Ellensburg. But you can look for one every night in the sky. The constellation Camelopardalis the giraffe is circumpolar from Ellensburg’s latitude of 47 degrees north meaning it is always above the horizon. Don’t expect to be overwhelmed by the appearance of the stars in Camelopardalis. The brightest star in the constellation appears only about half as bright as the dimmest star in the Big Dipper. However, the actual luminosities of the three brightest stars in Camelopardalis are very high, each at least 3,000 times more luminous than the Sun. Alpha Camelopardalis, a mind boggling 600,000 times more luminous than the Sun, is seven fists above the northern horizon at 9:00 p.m.

Friday: Draco Malfoy makes an appearance in all seven books of the Harry Potter series. Perhaps you’ve heard of these. But, the constellation Draco the dragon makes an appearance in the sky every night. It is a circumpolar constellation as viewed from Ellensburg meaning it never goes below the horizon. The head of the dragon is one fist above due north at 9:30 p.m. Eltanin, the brightest star in the constellation, is at the lower left-hand corner of the trapezoid-shaped head of Draco.

The positional information in this column about stars and planets is typically accurate for the entire week. For up to date information about the night sky, go to https://nightsky.jpl.nasa.gov/planner.cfm.