Thursday, July 28, 2016

The Ellensburg WA sky for the week of 7/30/16


Saturday: Mercury is less than a pinky width from Regulus. They are a half a fist held upright and at arm's length above the west-northwest horizon at 9 pm, with Mercury being the dot on top. The much brighter Venus is a little lower and to the right of the pair. 

Sunday: If you want to show your loved ones a celestial sign that they should hang up their clothes, show them Brocchi's Cluster, commonly known as the Coat Hanger cluster because of its resemblance to an upside down coat hanger. The cluster is six fists above the southeast horizon at 10:30 p.m., midway between Altair and Vega, the two brightest stars in the Summer Triangle. You'll need binoculars to make out the shape. First find Altair four fists above the southeast horizon. Slowly move your binoculars up toward Vega. You will run into the coat hanger along the way. And while you are at it, put away your shoes. 

Monday: In Scotland, August 1 was known as Lammas, the festival of the first wheat harvest of the year. You can remember this by looking at Spica, named after the Latin word for “ear of wheat”, one fist above the west-southwest horizon at 9:30 p.m. August 1 is known as a cross-quarter day, a day approximately half way between an equinox and a solstice. 

Tuesday: Seventeenth century astronomers documented the appearance of a new star, or “nova”, in 1670. However as modern astronomers studied the records of the star, called Nova Vulpeculae 1670, they realized it didn’t have the characteristics of a typical nova because it didn’t repeatedly brighten and dim. It brightened twice and disappeared for good. Turning their telescopes to the region, they discovered the chemical signature to be characteristic of a very rare collision of two stars. For more information about this discovery, go to http://goo.gl/rJnC2G. Nova Vulpeculae 1670 is right below the binary star system Alberio, the head of Cygnus the swan. Alberio is seven fists above the southeast horizon at 11 p.m. 

Wednesday: It’s a moonless August morning. The first remnant of dawn has not appeared yet. Suddenly, you notice a large softly radiant pyramid of light in the east sky. The base of this ghostly triangle is along the east horizon and the peak stretches two or three fists held upright and at arm’s length above the horizon about two hours before sunrise. Don’t be scared. It’s 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. This is one of the best times of year to see the zodiacal light in the morning. 
This is also one of the best times of the year to see meteors. The Perseid meteor shower peaks early next week. But you should see increased meteor activity later this week just below the W of the constellation Cassiopeia. This point is about two and a half fists above the northeast horizon at 11 p.m. By dawn, this point is about seven fists above the northeast horizon. 

Thursday: Do you want an easy way to find due north? A compass points to magnetic north, which is a few degrees off of true geographic north. Well, tonight’s your night. Capella, the brightest star in the constellation Auriga the Charioteer, is due north at exactly 9:23 p.m. It looks like a bright light on a pole on the north ridge because is only about one degree above the horizon. 

Friday: Jupiter is less than a pinky width above the crescent moon tonight. Catch them early because they set before 10 p.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 http://nightsky.jpl.nasa.gov/planner.cfm

Thursday, July 21, 2016

The Ellensburg WA sky for the week of 7/23/16


Are you planning to travel to London to see the new play, Harry Potter and the Cursed Child, which opens July 30? Then you better review some of the characters from the series.

Saturday: At 9:15 p.m., the bright star Regulus is about a half a fist held upright and at arm’s length above the west horizon. But, who is this Regulus? He has many potential identities. The most interesting from a pop culture standpoint is Regulus Black, the brother of Sirius Black who is Harry Potter’s godfather. Regulus Black was a former follower of Voldemort, the bad guy of the Harry Potter series. However, Regulus tried to dissociate himself from Voldemort and was killed. He would be in the pile of forgotten Harry Potter characters except that he is so interesting. Also, in the sixth book, Harry found an important note written by someone known only by the initials R.A.B. Hmmm. R.A.B. Regulus A. Black perhaps? Venus, Mercury, and Jupiter are near Regulus in the sky. Venus, the brightest of the four celestial objects, and Mercury are less than a fist to the lower right of Regulus and Jupiter is a little more than a fist to the upper left.

Sunday: But what does the “A” stand for? Anthony? Abercrombie? Alfonzo? Not astronomical enough. It stands for Arcturus, the second brightest star visible in the nighttime sky in Washington and at Hogwarts. Arcturus is four and a half fists above the southwest horizon at 10 p.m. The bright star Spica is below Arcturus, one third of the way up from the southwest horizon.

Monday: Bellatrix Lestrange is Sirius Black’s cousin. But, far from being kissing cousins. They are killing cousins. Bellatrix kills Sirius in a fight at the Ministry of Magic. Bellatrix the star is the third brightest star in the constellation Orion the hunter. It is one fist above the east horizon at 4:45 a.m.

Tuesday: Of course, Bellatrix is in cahoots with “he who must not be named”. Now, that’s a poorly written sentence, using an obscure synonym for “conspiring” and a vague reference. I must be under the curse “writicus dreadfulium”. Clearly this is the work of Tom Riddle, whose mother is named Merope Gaunt. Merope is a star in the Pleiades, an open star cluster nearly four fists above the east horizon at 4:30 a.m.

Wednesday: Draco Malfoy, Harry Potter’s young nemesis, is related to Sirius Black. Draco’s mother, Narcissa Black (Sirius’ cousin), helped develop a plan to trap Harry at the Ministry of Magic in the fifth book. Draco’s namesake, the constellation Draco the dragon, is one of the largest constellations in the sky, winding around the North Star. Draco’s head is a four-sided figure nearly straight overhead at 11 p.m.

Thursday: Saturn is two fists above the south horizon and Mars is a little less than two fists above the south-southwest horizon at 9:30 p.m. They are in the constellation Scorpius. Draco Malfoy was so impressed with this constellation name that he used it for the first name of his son.

Friday: Not every woman in the Black family is evil. Let’s focus on the good. Andromeda Black, Bellatrix’s sister, is a good witch and the mother of Tonks, a young witch from the last few Harry Potter books. (If these Harry Potter references are confusing, you better start reading the books.) Andromeda the constellation is an interesting one. It contains the Andromeda galaxy, the most distant object visible with the naked eye from a dark site. To locate the Andromeda Galaxy, first find the Great Square of Pegasus. At 11 p.m., the left hand corner of the square is about two and a half fists above the east-northeast horizon. Less than two fists to the left and down a little bit is another star the same brightness as the star at the corner of the square. From that star, hop about a half a fist up to a star that is about one fourth as bright. Less than another half fist in the same direction is a fuzzy oval patch of light known as the Andromeda Galaxy. The galaxy is impressive to see in binoculars. It consists of about 400 billion stars and is 2.2 million light years away.

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 http://nightsky.jpl.nasa.gov/planner.cfm.

Thursday, July 14, 2016

The Ellensburg WA sky for the week of 7/16/16

--> Saturday: Conjunction junction, what’s your function? Look to the west-northwest sky right after sunset to see a close conjunction of Mercury and Venus. Mercury is about a half a degree above the much brighter Venus. They are so close together in the sky, you could not even fit the full moon in between them. By about 9:30 p.m., they will have both set.

Sunday: The Southern Delta Aquarid meteor shower peaks for the next few weeks into mid-August. Meteor showers are named after the constellation from which the meteors appear to originate. These meteors appear to come from a point in Aquarius near the star Delta Aquarii, also known as Skat. This point is about one and a half fists held upright and at arm’s length above the southeast horizon at 1 am tonight. You can follow this point throughout the night, as it will remain a fist above Fomalhaut, the brightest star in that section of the sky. The best time to view the shower is just before morning twilight. For more information about this year’s shower, go to http://goo.gl/Uoxvda. As your Mother might say, dress warm and sit in a comfortable chair for maximum enjoyment. Meteors are tiny rocks that hit the Earth and burn up in the atmosphere.

Monday: Last week marked the one-year anniversary of NASA’s New Horizons probe passing by Pluto. If the band Nirvana was still together, they’d probably rewrite one of their hit songs to be called Heart-Shaped Spot, after one of Pluto’s most distinctive features. “She eyes me like a dwarf planet when I am weak. I’ve been imaging your heart-shaped spot for weeks.” Astronomers think this heart-shaped spot is a large plain of nitrogen ice that consists of convective cells 10-30 miles across. Solid nitrogen is warmed in the interior of Pluto, becomes buoyant, and bubbles up to the surface like a lava lamp. You will find great pictures and information about what New Horizons found this past year at http://pluto.jhuapl.edu/. Hey, wait, I’ve got a new complaint. People should be more interested in astronomy.

Tuesday: Jupiter is one and a half fists above the western horizon at 9:30 p.m.

Wednesday: Take a two and a half hour walk. Too long, you say? Forty-seven years ago today, Neil Armstrong and Buzz Aldrin took the first ever walk by humans on another world. They spend two and a half hours setting up scientific instruments and collecting rocks for study back on Earth. Michael Collins orbited the Moon in the spacecraft the astronauts would use to return to Earth.

Thursday: At 9:30 p.m., Saturn is a little more than two fists above due south and Mars is a little less than two fists above the south-southwest horizon.

Friday: Hot enough for you? If not, astronomers using NASA’s Spitzer Space telescope think they have discovered a planet with lava pools. This planet, called 55 Cancri e, is about twice the diameter of Earth and is tidally locked with its star, called 55 Cancri a (notice a pattern?). For more information about this discovery, go to http://goo.gl/wsEGRz.

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 http://nightsky.jpl.nasa.gov/planner.cfm.

Friday, July 8, 2016

The Ellensburg WA sky for the week of 7/9/16

Saturday: These next few weeks will be a great time to try see all five naked eye planets in the evening sky. Venus and Mercury are very low in the west-northwest sky right after sunset so they are the most challenging. But both are moving away from the Sun in the sky. By the end of the week, they will be right next to each other in the sky. Let’s start with an easy one tonight because it is a laid back Saturday. Jupiter is a fist held out at arm’s length to the lower right of the Moon at 10 p.m.

Sunday: Being in a coma is a bad thing. Looking at the Coma Star Cluster is a good thing. The Coma Star Cluster is an open cluster of about 50 stars that takes up more space in the sky than 10 full Moons. It looks like a fuzzy patch with the naked eye. Binoculars reveal dozens of sparkling stars. A telescope actually diminishes from the spectacle because the cluster is so big and the telescope’s field of view is so small. The Coma Star Cluster is in the faint constellation Coma Berenices (ba-ron-ice’-ez) or Queen Berenice’s hair. Queen Berenice of Egypt cut off her beautiful hair as a sacrifice to the gods for the safe return of her husband Ptolemy III from battle. The Coma Star Cluster is about three fists above the west horizon at 11:00 p.m. 

Monday: Tonight’s first quarter Moon is in the constellation Virgo. The bright star Spica is about a half a fist to the lower left of the Moon.

Tuesday: What you see with the naked eye isn’t all that can be seen. While astronomers can learn a lot from observing the sky in the visible wavelengths, many celestial objects radiate more light, and more information, in wavelengths such as radio, microwave, infrared, ultraviolet, x-ray, and gamma ray. In 2012, NASA launched the Wide-field Infrared Survey Explorer (WISE) to study objects that radiate in the infrared range such as asteroids, cool dim stars, and luminous galaxies. For an interesting comparison of how different wavelengths show different aspects of celestial objects, go to http://goo.gl/nvuax. For example, if it weren’t for infrared telescopes such as WISE, astronomers would not know about the significant amount of dust in galaxies. 

Wednesday: The long summer days remind us to take some time to safely observe the Sun. The best way to do that is to go to http://sdo.gsfc.nasa.gov/ and watch the great images and videos that come from the Solar Dynamics Observer, or SDO for short. We are moving toward a sunspot minimum so the Sun has not been very active lately. So what, you say? Sunspots and associated phenomena greatly influence the strength of solar flares. The strongest flares can affect satellites orbiting the Earth and even electronics on the Earth’s surface. So, an inactive Sun means our satellites are safer. That means you will be able to call your friends on your cell phone when you see the elusive Mercury and the much brighter Venus low in the west-northwest sky a few minutes after sunset.

Thursday: The Moon joins a crowded part of the sky tonight. At 10 p.m., Saturn is a little over two fists and the bright star Antares is one and a half fists above due south. Mars, the brightest point of light in the region, is one fist below the Moon.

Friday: Say "Cheese". 166 years ago Vega, in the constellation Lyra the lyre, became the first star ever photographed. The photograph was done at the Harvard Observatory using the daguerreotype process. Vega is the third brightest nighttime star we can see in Ellensburg, behind Sirius and Arcturus. Vega is nearly straight overhead at 11:00 tonight. 

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 http://nightsky.jpl.nasa.gov/planner.cfm 


Wednesday, June 29, 2016

The Ellensburg WA sky for the week of 7/2/16

Saturday: Look straight up at midnight. The head of Draco the dragon will be looking straight down on you. The brightest star in the head is called Eltanin. If you chose to wait a VERY long time, Eltanin will be the brightest star in the night sky. Currently 154 light years away, it is moving towards Earth and will be only 28 light years away in about 1.3 million years, claiming the title as brightest star.

Sunday: Jupiter is nearly two fists held upright and at arm’s length above the west horizon at 10 p.m. So is the NASA Juno spacecraft because tomorrow it reaches its destination after a nearly five-year trip to Jupiter to study the giant planet’s core, atmosphere, and magnetic field. By learning more about Jupiter, astronomers hope to learn more about the formation and evolution of the Solar System. If the latest blockbuster, Independence Day: Regurgitate disappointed you, watch the more engaging sci-fi-film-like trailer about the Juno mission at https://youtu.be/SgEsf4QcR0Q.

Monday: Hot enough for you? Don’t blame the Earth-Sun distance. Surprisingly, the overall temperature of the Earth is slightly higher in July, when the Earth is farthest from the Sun, than in January, when it is closest. That’s because in July, the Northern Hemisphere is tilted towards the Sun. (This is the real cause of the seasons.) The Northern Hemisphere has more land than the Southern Hemisphere. Thus, in July, the large amount of Northern Hemisphere land heats up the entire Earth about two degrees Celsius warmer than in January. In January, the watery Southern Hemisphere is tilted toward the Sun. But, water does not heat up as fast as land so the Earth is a few degrees cooler. The distance between the Earth and Sun is its greatest today, 152.1 million kilometers. This is called aphelion from the Greek prefix “apo” meaning “apart” and Helios, the Greek god of the Sun.

Tuesday: Tonight, while you are taking a break from looking at an explosion of fireworks, the NASA Kepler spacecraft is taking a break after finding an “explosion” of exoplanets. In May, astronomers announced the discovery of 1,284 new planets, more than doubling the number of planets discovered by Kepler. 550 of those are small and possibly rocky. Nine of those are in the habitable zone of their host star. And this is only the beginning. The Kepler spacecraft is monitoring the brightness of over 156,000 stars in the constellations Cygnus the swan and Lyra the lyre. This region is midway between the bright stars Deneb and Vega. It is about the size of your hand held at arm’s length and is about six fists held upright and at arm’s length above due east at 11 p.m. For more information about this find, go to http://goo.gl/Hll9pI.

Wednesday: Mars is two fists above due south at exactly 9:21 pm. The bright reddish star Antares is one and a half fists above due south at exactly 10:30 pm. Saturn is two fists above due south at exactly 10:37 pm. I still love formulaic writing. Notice that these times are about a half hour earlier than when these same objects were above due south eight days ago. In general, distant objects rise earlier from night to night. Stars rise about four minutes earlier each night, as evidenced by our observation tonight and last Tuesday.

Thursday: Last week, I wrote about Mizar. This week, I need to warn you not to confuse Mizar with its rhyming brother Izar in the constellation Bootes. Izar is also a binary star with about the same apparent brightness. And both were featured in different episodes of Star Trek. Izar was featured in the Star Trek episode “Whom Gods Destroy” from the original series. It is the base of Fleet Captain Garth, a former big shot in the federation and one of Kirk’s heroes before he went insane. Garth kidnaps Kirk and Spock before eventually being out smarted. Mizar doesn’t play as big a role in its episode. It is the star of the home world of one of the alien species in The Next Generation episode “Allegiance”. Izar is one fist above the bright star Arcturus and seven fists above the south horizon at 10 p.m. Mizar is seven fists above the northwest horizon at this time.

Friday: Venus is just above the northwest horizon at 9:15 p.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 http://nightsky.jpl.nasa.gov/planner.cfm.

Friday, June 24, 2016

The Ellensburg WA sky for the week of 6/25/16


Saturday: “Mom, I can’t sleep. It is too light out!” A poor excuse you say? Good astronomy skills, I say. The latest sunset of the year happens this week. Surprisingly, the earliest sunrise and the latest sunset do not both happen on the longest day of the year, the day of the summer solstice. The earliest sunrise occurs just before the longest day and the latest sunset occurs just after the longest day. This phenomenon relates to the angle of the Sun’s path near rising and setting. In Ellensburg, that angle is about 66 degrees near the first day of summer. Because of the Earth’s orbit, which causes the Sun’s apparent motion, the angles are not symmetric. The asymmetries in orbital angles leads to the asymmetry in rise and set times. By the way, picking a specific night to give you the “can’t sleep because it is too light out” line may just be an excuse because the sunset times change by only a few seconds each day in June. This year, the sun sets between 9:01 and 9:02 p.m. between June 21 and July 2.

Sunday: Jupiter is about two fists held upright and at arm’s length above the west-southwest horizon at 10 p.m.

Monday: Don’t wait until a week from today to go to those wimpy firecracker shows. Find the hypergiant star Rho Cassiopeiae. Astronomers think that Rho Cassiopeiae will likely go supernova (explode) in the near future. Of course, for stars, near future might mean today. It might mean 20,000 years from now. Rho Cassiopeiae is in the constellation Cassiopeia the queen. At 11:00 tonight, Cassiopeia looks like the letter “W” about three fists held upright and at arm’s length above the northeast horizon. Rho Cassiopeiae is about a finger’s width to the right of the rightmost star in the “W”. Once you find it you’ll be thinking, “Big deal, I can hardly see it.” Although it is barely visible to the naked eye, it is actually very bright. It is the 20th most luminous star in the sky, a whopping 550,000 times more luminous than the Sun.

Tuesday: Mars is two fists above due south at exactly 9:51 pm. The bright reddish star Antares is one and a half fists above due south at exactly 11:01 pm. Saturn is two fists above due south at exactly 11:00 pm. I love formulaic writing.

Wednesday: Star light. Star bright. The first star you see tonight might be Arcturus, six fists above the south horizon right after sunset. You’ll be able to see either Jupiter or Mars earlier but they won’t facilitate your wish coming true.

Thursday: Happy Asteroid Day (http://www.asteroidday.org/), the day we celebrate avoiding the destruction of the Earth by an undiscovered asteroid. There are a million asteroids in the Solar System with the potential to strike Earth and destroy a city. Astronomers have discovered only 1% of them. Asteroid Day is an effort to educate the public and encourage policy makers to fund this important effort. King Tut may have celebrated an ancient Asteroid Day by asking his assistants to make a dagger out of a broken-off asteroid that landed on Earth. Astronomers discovered that the blade of the knife contained much more nickel than is found in terrestrial iron, an amount consistent with iron meteorites, especially with one found 16 years ago in northern Egypt. For more information about the dagger, go to http://goo.gl/BHBivd.

Friday: Mizar is a well-known binary star in the constellation Ursa Major. You can find it at the bend in the Big Dipper handle, nearly straight overhead at 10 p.m. tonight. Its name is Arabic for waistband. Mizar has an optical double called Alcor, which is less than a pinky width away and can easily be seen with the naked eye. Optical doubles are stars that are close together in the sky but do not orbit a common center of mass as true binary stars. Not wanting to deceive sky gazers who call Mizar a binary star, two stars that DO orbit a common center of mass, Mizar actually is a binary. It was the first binary star system discovered by telescope. Mizar A and Mizar B are about 400 astronomical units apart from each other and about 80 light years from Earth. 400 astronomical units is about 10 times the distance between the Sun and Pluto.

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 http://nightsky.jpl.nasa.gov/planner.cfm.

Wednesday, June 8, 2016

The Ellensburg WA sky for the week of 6/18/16


Saturday: Father’s Day is tomorrow. Do you have a dad so great that you wish you could write his name in the galaxies? Now you can. UK astronomer Steven Bamford has developed a computer program that finds images of galaxies that resemble different letters. Just enter the words here http://mygalaxies.co.uk/ and the program spells it out in galaxies. Here’s the new Daily Record title page http://mygalaxies.co.uk/jh2m7m/.

Sunday: Tonight’s full moon is in the constellation Sagittarius the Archer. This month, Sagittarius may be thinking of shooting strawberries instead. Some Native American tribes call the June full moon the strawberry moon to honor (or remember) the short strawberry harvesting season. A more descriptive name is the Short Moon because the full moon is above the horizon for the least amount of time in June – only eight hours. Summer full moons are always above the horizon less than winter full moons. Since the full moon is on the complete opposite side of the Earth as the Sun, the full moon is going to be in the sky whenever the Sun is not in the sky, namely the entire night. During the summer, the nights are shorter so the full moons time above the horizon will also be shorter.

Monday: Today is the first day of summer, the day that the Sun reaches its highest declination (the official name for sky latitude) of 23.5 degrees above the celestial equator. The celestial equator is the line that divides the northern sky from the southern sky. In Ellensburg, the Sun is about seven fists held upright and at arm’s length above the south horizon at 1:00 p.m. (noon standard time). Contrary to popular belief, the Sun is never straight overhead in Ellensburg or anywhere else in the 48 contiguous states. The northernmost portion of the world where the Sun can be directly overhead is 23.5 degrees north latitude. In ancient times, the Sun was in the constellation Cancer the crab on the first day of summer. Hence, 23.5 degrees north latitude has the nickname "Tropic of Cancer". Because the Earth wobbles like a spinning top, the Sun's apparent path through the sky changes slightly over time. Now, the Sun is in the constellation Taurus the bull on the first day of summer. However, citing the high cost of revising all of the science books, geographers are not changing the name of 23.5 degrees north latitude to "Tropic of Taurus". The first day of summer is often called the summer solstice. However, astronomers refer to the summer solstice as the point in the sky in which the Sun is at its highest point above the celestial equator. Thus, summer starts when the Sun is at the summer solstice point. This year, that happens at 3:34 p.m. Pacific Daylight Time.

Tuesday: Saturn and Mars are both nearly exactly two fists above the south horizon at 11 p.m. Saturn is a little east of due south and Mars is a little west of due south.

Wednesday: When it is sitting low in the western sky, many people mistake the star Capella for a planet. It is bright. It has a slight yellow color. But, Capella is compelling on its own. It is the fourth brightest star we can see in Ellensburg. It is the most northerly bright star. It is a binary star consisting of two yellow giant stars that orbit each other every 100 days. At 10 p.m., Capella is two fists above the north-northwest horizon. If you miss it tonight, don’t worry. Capella is the brightest circumpolar star meaning it is the brightest star that never goes below the horizon from our point of view in Ellensburg.

Thursday: Jupiter is two and a half fists above the west-southwest horizon at 10 p.m.

Friday: Nearly 400 years ago, Galileo viewed the Pleiades star cluster through his telescope and saw that the seven or so stars in the region visible to the naked eye became many more. There are two main types of star clusters. Open star clusters are groups of a few dozen to a few thousand stars that formed from the same cloud of gas and dust within our galaxy. Stars in open star clusters are young as far as stars go. Globular clusters are groups of up to a few million stars that orbit the core of spiral galaxies such as our own Milky Way. One of the most well known star clusters is the globular cluster in Hercules, an object that is fairly easy to find with binoculars. First find Vega, the bright bluish star five fists above the east horizon at 11 p.m. Two fists above Vega is a keystone shape. Aim your binoculars at the upper left hand star of the keystone. The globular cluster is one third of the way to the rightmost star of the keystone. It looks like a fuzzy patch on the obtuse angle of a small obtuse triangle. If you don’t know what an obtuse angle is, you should not have told your teacher, “I’ll never need to know this stuff”.

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 http://nightsky.jpl.nasa.gov/planner.cfm.