In the Sky This Week – August 22, 2017
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Sirius, the “Dog Star,” accompanies Venus low in the eastern predawn sky. Jupiter sets shortly after dusk and will vanish from view entirely in a early September. Saturn is high in the southern sky, and with the planet’s northern hemisphere tilted towards us at about 26°, Saturn is just a spectacular observing target. The Moon, fresh from the eclipse, will be in conjunction with Jupiter in the west at dusk on August 24th and 25th. The Moon will be a waxing crescent in the west at dusk, growing larger each evening until it is at first quarter on August 28th; the later part of this week will be excellent nights for star parties. Sirius, the brightest star in Earth’s sky, is a binary star system about 8.6 light years away. Sirius A is a bright and hot main sequence star, with a faint white dwarf companion: Sirius B. Sirius A is class A0 star about twice the mass of the … Continue reading

In the Sky This Week – August 15, 2017
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Venus is a bit lower and Orion a bit higher in the eastern morning sky. Venus orbits closer to the Sun than Earth, and is racing ahead-of and away-from the Earth; the planet will vanish from view in mid-November as the Sun comes between it and the Earth. The waning crescent Moon appears thinner and closer to the horizon each morning in the eastern sky. Note: I used Stellarium’s new “Astronomical calculations” feature to generate the ephemeris for this image – I expect you’ll be seeing more of this. The Moon be in conjunction with the star Aldebaran on the Aug. 16th, appearing VERY close to each other, VERY early in the morning. Aldebaran is a orange giant star about 44 times the size of the Sun, located about 65 light years away. Aldebaran is positioned close to the ecliptic plane, and is frequently occulted by the Moon… just not this month. Jupiter is visible only for a short time … Continue reading

In the Sky This Week – August 8, 2017
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Venus is a bit lower in the eastern predawn sky, and Orion is fully visible now before sunrise. The waxing gibbous Moon, just days after full,  rises in the east with the sunset, and sets in the west with at dawn. Jupiter is low in the western sky, and visible for only a short time. Saturn is high in the southern sky after sunset, and sets about 2:00 AM. The Perseid Meteor shower peaks the evening of August 11-12th; the Moon will be at Third-Quarter on August 14th. Apps used for this post: Stellarium: a free open source planetarium app for PC/MAC/Linux. NASA Eyes on the Solar System: an immersive 3D solar system and space mission app – free for the PC /MAC. Also in In the Sky This Week Weekly post on what you can see in the sky. In the Sky This Week – June 22, 2017 In the Sky This Week – June 27, 2017 In the Sky This … Continue reading

In the Sky This Week – August 1, 2017
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Venus is still high in the eastern morning sky; the constellation Orion appears a bit higher each morning. The southern sky is filled with objects this week: the waxing gibbous Moon accompanies Jupiter and Saturn for several days. The Moon will appear very close to Saturn on the evening on August 2nd. The constellation Cetus appears in the predawn sky to the southeast. Cetus is depicted as a sea monster in Greek mythology, but is often referred to as “the whale” today. I know several astronomers who had a copy of H.A. Rey’s “The Stars: A New Way to See Them” when they were young – I still have my copy! I was overjoyed to see that Stellarium has a starlore set depicting constellations as drawn by H.A. Rey in his book. The constellation Cetus in Stellarium as drawn by H.A. Rey in his book “The Stars: A New Way to See Them.” The sky overhead – Aug 1, 2017 … Continue reading

In the Sky This Week – July 25, 2017
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Venus is still bright in the eastern predawn sky, but a little bit lower each morning. The constellation Orion is rising with the dawn; a little more of the constellation visible each morning. A wafer-thin waxing crescent Moon will be visible for a short time after sunset in the west on July 25th. Jupiter is visible low in the southwestern sky, and will be a little lower in the sky each evening after sunset. Saturn is high in the southern sky, and is a great target for telescope observers. Jupiter will be a scant 3° South of the Moon after sunset on July 28th. The Moon will be at First Quarter on the evening of July 30th, surrounded by Jupiter and Saturn, and the Southern Delta Aquariids Meteor Shower peaks on July 29-30th; this would be a great evening to host an astronomy outreach event! Apps used for this post: Stellarium: a free open source planetarium app for PC/MAC/Linux. NASA … Continue reading

In the Sky This Week – July 18, 2017
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Venus continues to dominate the morning sky in the east, but appears slightly lower in the sky each morning as it pulls ahead of us in its orbit. The waning crescent Moon will appear near Venus the the star Aldebaran on the mornings of July 19th and 20th. The New Moon will be on the 23rd. Jupiter and Saturn appear in the south-southwestern sky after sunset; Jupiter will appear slightly lower in the western sky each day as the Earth pulls ahead of Jupiter in its orbit. The constellations Pegasus and Andromeda appear low in the northeast sky after sunset; the wispy cloud of M31, the Andromeda galaxy, makes a good target for telescope observers. M31 is the nearest major galaxy to the Milky Way. It is 2.5 million light years distant, and heading straight at us; in a little over 4 billion years, it will collide with the Milky way, and the two galaxies will merge into a large … Continue reading

Jupiter’s Great Red Spot from Juno
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The Juno spacecraft made its seventh close approach (perijove) to Jupiter on July 10th, flying directly over the Great Red Spot. The raw images from the mission are publicly available, and have been post-processed by several different individuals. The results are as beautiful as they are varied. This stunning image, processed by Seán Doran, was featured on the Astronomy Picture of the Day on July 15, 2017: Here are some more examples of post-processing from the imaging community: This image was processed by Jason Major, who runs the fantastic Lights in the Dark website; the image was used in this post by NASA. This video was created using the NASA’s Eyes on the Solar System app shows the Juno spacecraft coming up on the Great Red Spot; I knew the storm was big, but I’ve never seen it from this perspective… it’s BIG! This video gives you a good idea of how close the Juno spacecraft gets to Jupiter during … Continue reading

In the Sky This Week – July 11, 2017
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Venus continues to be the “morning star” in the east, and will appear very close to the red giant star Aldebaran – the “eye of the bull” in the constellation Taurus. On the 11th, Venus will be 3◦ north of Aldebaran, over the course of the week, Venus’ day to day change in position relative to Aldebaran will be very noticeable. In the west, bright stars Vega and Altair are the last to fade in the oncoming dawn. On the 11th, a waning gibbous Moon will be rise in the east before midnight, and set in the west around 9:00 AM. On the 18th, a waning crescent Moon will rise shortly after 2:00 AM, and be visible until it is lost in the glare of the rising sun after 6:00 AM. The Moon will be at third quarter on the 16th, and will be visible from about 1:00 AM – 1:00 PM.* Jupiter and Saturn are visible in the southern sky … Continue reading

In the Sky This Week – July 4, 2017
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Venus is the bright morning star in the eastern sky, attended by the Pleiades star cluster, and the bright star Capella to the northeast. The southern sky is adorned with several jewels this week: the Moon appears high in the southern sky before sunset as a waxing gibbous – a few days past first quarter. Jupiter and Saturn are both visible, as are the bright stars Antares and Spica. The full Moon will be on July 9th. The bright star Altair (featured in the classic SF film Forbidden Planet) rises in the east followed by the constellation Sagittarius to the southeast. Sagittarius is recognizable by “The Teapot” asterism low on the horizon. Sagittarius has several interesting deep sky objects to observe using telescopes; something cool you can do with the public during nighttime observing sessions is point to the Teapot’s spout and say “that’s where center of our Milky Way galaxy is!” Before dawn, the constellation Hercules sets in the west, and “The … Continue reading

In the Sky This Week – June 27, 2017
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Venus remains high in the eastern morning sky, the Pleiades star cluster appears between Venus and the star Capella. The Moon is a waxing crescent, appearing in the west after sunset. Jupiter is high in the southwest, and Saturn is low in the southeast sky after sunset. There will be a conjunction of the Moon, Jupiter and the star Spica on the evenings of June 30th and July 1st. Here is the current positions of the planets in the solar system: Also in In the Sky This Week Weekly post on what you can see in the sky. In the Sky This Week – June 22, 2017 In the Sky This Week – June 27, 2017 In the Sky This Week – July 4, 2017 In the Sky This Week – July 11, 2017 In the Sky This Week – July 18, 2017 In the Sky This Week – July 25, 2017 In the Sky This Week – August 1, 2017 … Continue reading

In the Sky This Week – June 22, 2017
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The planet Venus appears high in the eastern morning sky; the bright star Capella, to the northwest, is the last star to fade with the oncoming dawn. The waning crescent Moon will vanish amid the morning haze to the east, to reappear in the west as a waxing crescent after dusk on June 25th. The Summer Triangle is an asterism formed from the three stars Altair, Deneb, and Vega, the brightest stars in the three constellations of Aquila, Cygnus, and Lyra. They can be see in the eastern sky before midnight. Jupiter is high in the southwestern sky after dusk, and sets in the west around 1:30 AM. Saturn appears high in the southeastern sky after dusk, is at its highest around midnight, and sets in the southwest just before dawn. Directly overhead, the Milky Way flows through the constellations Cygnus and Aquila (if you live in a city – trust me, it’s really there… drive out of the city … Continue reading

Revealed Through Reason: The Phases of the Jovian Moons
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In 1614 Johann Georg Locher, a student of the Jesuit astronomer Fr. Christoph Scheiner, published a short book called Disquisitiones mathematicae, de controversiis et novitatibus astronomicis—that is, Mathematical Disquisitions, Concerning Astronomical Controversies and Novelties. Among other things, the book discussed the phases of Venus and the satellites of Jupiter, all recently discovered by Galileo using a telescope. Toward the end of the book, Locher engaged in an interesting exercise in astronomical reasoning. He presented to his readers the figure below. And, regarding this figure, he wrote— Vnam hactenus Lunam agnouimus circa terram, quam oculus A in terra positus libere conspexit, modo silentem in B; modo dimidiam in C; alias plenam in D; alias curtatam in E…. At vero, post repertum Oculum Astronomicum, tubum inquam Opticum, plures sese aperuerunt nobis Lunae.   Quarum praecipua videtur esse Venus; ea enim in tubum GH ex I delapsa, oculo A occurrit falcata, dum puncto M Augis opposito vicina agit: & vero in K Auge … Continue reading