Tag: Stargazing

Skies over Milton, May Edition

By Peter Forrester | May 9, 2019

Greetings, stargazers, wherever you may be! Apologies for the long delay in writing this update – I have been dealing with some personal issues which took up a great deal of my time every day, for about the last month, but that has now been resolved.

So here are your skywatching tips for this “Merry Month of May”!

Past events (included only for completeness, except for the meteor shower which is ongoing):

Thursday, May 2: Moon near Venus, morning sky at 11:00 AM (Eastern Daylight Time)

Friday, May 3: Moon near Mercury, morning sky at 6:00 AM.

Saturday, May 4: New Moon at 6:46 PM.

Monday, May 6: Three events: Moon near Pleiades (open cluster) at 1:00 AM.

Also, the peak of the Eta Aquariid meteor shower occurred at 10:00 am (most visible for a 7-day period around this peak, still visible now just above the horizon before dawn). This meteor shower is formed by debris that separated from Halley’s Comet hundreds of years ago. Easier to see in the Tropics and in the Southern Hemisphere. The shower lasts until Tuesday, the 28th of May.

Third, the Moon was near the bright star Aldebaran at 6 PM.

Tuesday, May 7: The Moon was near Mars at 9:00 PM.

Future events: 

Thursday, May 9: The Moon will be near the bright star Pollux (one of the bright ones in Gemini) at 11:00 PM.

Saturday, May 11: First Quarter Moon at 9:12 PM.

Monday, May 13: Moon will be at perigee (closest to Earth in the current orbital period) at 5:54 PM.

Saturday, May 18: Full Moon at 5:10 PM.

Tuesday, May 21: Mercury will be at superior conjunction (meaning it is directly behind the Sun) with the Sun at 9:00 AM. After this it will pass into the evening sky.

Wednesday, May 22: Moon will be near Saturn at 4:00 PM. People in South Africa will be able to see an “occultation”, meaning that Saturn will be behind the Moon.

Sunday, May 26: Moon at apogee (furthest from the Earth) at 9:00 AM. Also, Last Quarter Moon at 12:33 PM.

Tuesday, May 28: Ceres will be at opposition at 6:00 PM. This means that it is in a straight line with the Earth and Sun, with the Earth in the middle. This is when it is brightest, but at apparent magnitude of 6.7, it is still too dim to see with the naked eye unless you have extremely dark skies.

Ceres is the largest object in the Main Asteroid belt between Mars and Jupiter, and the only “dwarf planet” there. It was the first asteroid to be discovered, way back in 1801. The NASA spacecraft Dawn orbited Ceres from 2015 to 2018, see the reference below for more information on this fascinating space body.

For more skywatching events (including some in the free download PDF that involve the Moon being near various objects which I omitted), or to see the events in Universal Time or ones that are not visible from my location in Milton, New Hampshire, see http://Skymaps.com/skycalendar/.

Previous in series: Skies Over Milton, April Edition

References:

Thalassoudis, Kym. (2000-19). Skymaps. Retrieved May 9, 2019 from skymaps.com.

Wikipedia. (2019, May 8). Ceres (dwarf planet). Retrieved from https://en.wikipedia.org/wiki/Ceres_(dwarf_planet).

Wikipedia. (2019, April 20). Conjunction (astronomy)#Superior and inferior. Retrieved from https://en.wikipedia.org/wiki/Conjunction_(astronomy)#Superior_and_inferior

Wikipedia. (2019, May 4). Eta Aquariids. Retrieved from https://en.wikipedia.org/wiki/Eta_Aquariids.

Wikipedia. (2019, May 8). Opposition (astronomy). Retrieved from https://en.wikipedia.org/wiki/Opposition_(astronomy).

Circumpolar Constellations: Ursa Major

By Peter Forrester | April 18, 2019

Greetings all! Let’s talk about one of the best-known group of stars (not a constellation) in the sky.

Yes, I mean the Big Dipper, which is referred to as an “asterism,” or a collection or shape of stars that are not recognized as a constellation (the 88 “official” ones were defined in 1928, at a meeting of the International Astronomical Union, which just celebrated its 100-year anniversary a few days ago).

Officially, by the way, a constellation is a region in the sky, not just a set of bright stars that form a shape but everything around them as well. For instance, when the Sun, Moon, or a planet is in the same direction as a constellation we say that it is “in” that constellation. The same is true of comets, asteroids, nebulas, quasars, pulsars, black holes, whole galaxies, or even dust. Every point in the sky is defined as belonging to one or more constellations (the “more” being along the borders).

But back to the asterism known as the Big Dipper. In this case, the 7 stars that make up the Dipper (called the Plough in the U.K.) are part of the constellation Ursa Major (the Great Bear).

I have not covered the Big Dipper until now because as of a few months ago, it was still very low to the horizon in the early evening, and thus not very visible if you have any kind of treeline.

Six of the seven stars in the Dipper are of 2nd degree magnitude, and the other one is 3rd degree. They are the brightest stars in Ursa Major.

Many of my readers will already know that the Big Dipper, as I said about Orion, can be used to find other stars and constellations easily. Tracing the side of the bowl upward, the line extends to Polaris, the North Star, which is part of the constellation called Ursa Minor. This is very useful for nighttime navigation without a compass, as Polaris is always located to the north. Sailors have been using the stars to find their direction for millennia, and the Big Dipper was what they used to locate Polaris, since Polaris is only 3rd degree and looks similar to every other star of the same color and brightness.

Using the same two stars that form a line to Polaris, tracing the line in the opposite direction brings you to another bright constellation, one of the Zodiac: Leo the Lion, whose shape resembles a rectangle that touches a backwards question mark. Thirdly, following the curve of the handle brings you to the constellations Bootes (resembling a kite, its brightest star called Arcturus) and Virgo (brightest star Spica). Hence the once-popular saying “Arc to Arcturus, and spike to Spica”). There are some other lesser known direction-finding lines using different stars in the Big Dipper, see the Big Dipper reference below if you want to know more about this.

Ursa Major is very close to the north celestial pole, and thus as explained previously, it  is circumpolar. Therefore, meaning it never sets from the sky when seen from northern latitudes such as the United States or Europe, but appears to go in a circle every 24 hours around Polaris, the star located directly over the North Pole of Earth.

Incidentally, the Big Dipper has been considered as the tail of a bear, and various other images (this one makes no sense because bears don’t have long tails). The rest of the bear consists of dimmer stars to the right of and below the bowl when it is lying flat on its bottom (the bowl to the right of the handle – it is close to the horizon when it is in this direction).

In popular culture, the Big Dipper is found on the flag of the state of Alaska, and a few other flags and coats of arms. It may even be mentioned in the Bible (its reference in the book of Job is disputed by scholars).

I once made a scale-model view of the distance of the stars in the Big Dipper, a side-view, if you will. One of the stars was so much further than the rest that I had to mount it on a separate piece of cardboard from the rest. This was a school project, and unfortunately I no longer have it. But it is interesting to note that the shapes we see are only from our perspective, and most constellations would appear very different in other solar systems.

I’m going to leave the discussion there, because I’m feeling a bit under the weather, but I wish you all the best time while skywatching, and be sure to look up when you go out!

Previous in series: Circumpolar Constellations: Cassiopeia

References:

Wikipedia. (2019, March 10). Asterism (astronomy). Retrieved from https://en.wikipedia.org/wiki/Asterism_(astronomy).

Wikipedia. (2019, April 2). Big Dipper. Retrieved from https://en.wikipedia.org/wiki/Big_Dipper.

Wikipedia. (2019, April 1). Constellation. Retrieved from https://en.wikipedia.org/wiki/Constellation.

Wikipedia. (2019, March 29). Ursa Major. Retrieved from https://en.wikipedia.org/wiki/Ursa_Major.

Skies Over Milton, April Edition

By Peter Forrester | April 2, 2019

Greetings on this fine sunny day! (I wish I could call it “warm”!)

Here are your monthly skywatching events, including one that already occurred. Note: all times are in US Eastern Daylight Savings Time (EDT) unless otherwise noted, which is 4 hours less than Universal Time (UT). Note: not all of these events occur at a time where the sky in Milton will be dark enough to see them.

Tuesday, April 2: Moon near Venus, 3:00 am EDT. Also Moon near Mercury, 10:00 PM.

Friday, April 5: New Moon at 4:51 AM. This is the start of “Lunation 1191” (a lunation is about 29.53 days, or the time between one new moon and the next. The exact length of a lunation varies a little bit, see the reference on “New moon” for more information).

Monday, April 8: Moon near the Pleiades at 7 pm.

Tuesday, April 9: Moon near Mars at 6 am (evening sky). Moon near Aldebaran (brightest star in constellation Taurus) at noon (in evening sky).

Friday, April 12: First Quarter Moon at 3:05 PM.

Sunday, April 14: Mars near Aldebaran at 9 pm.

Friday, April 19: Full Moon at 7:11 AM.

Monday, April 22, Lyrid Meteor Shower peaks at 8 pm. It is visible from the 14th to the 30th. 10 – 20 fast, bright meteors per hour during the peak, unfortunately the Moon’s brightness well make these meteors harder to see. The meteors can be seen all over the sky, but the radiant (point of origin) is between the constellations Lyra and Hercules.

Tuesday, April 23: Moon near Jupiter, 9:00 AM.

Thursday, April 25: Moon near Saturn at 9:00 AM (occultation, which means the nearer object passing in front of the other and therefore blocking light from it, will occur. In this case, the occultation will only be visible in parts of Australia, New Zealand, and South America).

Friday, April 26: Last Quarter Moon at 6:18 PM.

For more of these events, or to check out other skywatching tips, be sure to visit skymaps.com.

Until my next, enjoy the skies, and this glorious spring which is now upon us (at least in the Northern Hemisphere)!

Previous in series: Skies Over Milton, March Edition

References:

Thalassoudis, Kym. (2000-19). Skymaps. Retrieved April 2, 2019 from skymaps.com.

Wikipedia. (2019, March 25). Lyrids. Retrieved from https://en.wikipedia.org/wiki/Lyrids.

Wikipedia. (2019, January 10). New moon. Retrieved from https://en.wikipedia.org/wiki/New_moon.

Wikipedia. (2019, March 10). Occultation. Retrieved from https://en.wikipedia.org/wiki/Occultation.

Observing the Planets: Jupiter

By Peter Forrester | March 28, 2019

Jupiter, as seen from the surface of the Earth, is on average the second brightest of the five visible planets. Only Venus is brighter (and sometimes Mars). This is reflected light from the Sun, as planets don’t produce any light of their own. Jupiter’s reflected light is bright enough to cast shadows on Earth (the brightest apparent magnitude it reaches is -2.94).

Being so bright, Jupiter has been known since ancient times, and was thought to represent the god Marduk to the Babylonians, and the gods Zeus and Jupiter in Greek and Roman mythology, the last of whom it is named for.

Unlike Venus and the Moon, Jupiter doesn’t go through a full range of phases, being more distant from the Sun (at times as much as 11.5% of the side we see is not illuminated, so it does have the Full and Gibbous phases only). It also takes 11.86 years to orbit the Sun, meaning it will move about 30 degrees in the sky every year (the twelve years of the Chinese calendar were originally based on this orbital period). So it can be hard to remember where it is located, but it (and even more so the more distant planets) tend to move very slowly among the stars, lingering in the same constellation for months to years. This is an advantage if you can remember where to look. Jupiter will take many months to cross Ophiuchus, since it is a very large constellation.

We just passed an occasion a couple of days ago where the Moon was located very close to Jupiter. But how can you find it normally?

Jupiter has just entered the constellation Ophiuchus, the “13th zodiac” constellation, located above Scorpius. According to the planet locator on timeanddate.com (see link below), it will be above the horizon (from their nearest location to Milton in Concord, New Hampshire) between 1:24 and 10:25 am tomorrow.

If you have a smartphone, you can also find the current location of any planet on the free app Sky Map (you have to make sure the constellation labels are on and follow the Zodiac constellations around to find all the planets, Moon, and Sun). You can find some other excellent websites by doing a simple Google search.

Observing Jupiter with the naked eye, it just looks like a very bright yellowish star. However, if you have a chance to look at it in a telescope, which I have had the pleasure to do, I suggest you take it. You can see its round shape, including the aforementioned Great Red Spot, as well as the many belts of clouds and some or all of the four Galilean moons, whichever happen to be on the same side. The whole planet will be lit up because we are between Jupiter and the Sun right now.

Stay tuned for more on this amazing object in the sky. Have fun watching Jupiter, and pleasant star-gazing!

Previous in series: Observing the Planets: Venus

References:

Time and Date A.S. (1995-2019). Night Sky Map & Planets Visible Tonight. Retrieved from https://www.timeanddate.com/astronomy/night/.

Wikipedia. (2019, March 26). Jupiter. Retrieved from https://en.wikipedia.org/wiki/Jupiter.

Observing the Moon: Part 2, Just What is a Super-Moon Anyway?

By Peter Forrester | March 20, 2019

Well, here we go. Another supermoon is coming up tonight / tomorrow (depending on where you are), right after the Spring Equinox which is tonight about 6 pm in US Eastern time. This one is called the Super Worm Equinox Moon, or similar phrases. What exactly do all these terms mean?

Well, first of all, “supermoon” means a Moon that is at its closest approach to Earth, and at full moon (or new moon) phase at the same time, making it appear brighter and slightly larger than it normally would. Every month it has its “perigee”, the closest approach of that orbit, and the opposite “apogee”, but some perigees are closer than others. The moon at perigee normally appears about 14% bigger than at apogee, so we’re not talking a huge difference here.

The term supermoon was first coined by an astrologer in 1979, and has various definitions in different places. The original definition stated that the full or new moon occurs with the Moon within 90% of its closest approach to Earth, but the reason for choosing 90% was never explained, and the claim that a supermoon causes catastrophic effects and stress on Earth has been thoroughly disproven by scientists. It should also be noted that most people using the term “supermoon” are referring to a Full Moon (and very rarely is used for a New Moon).

The Worm refers to the month of March, and apparently this originates with Native Americans who called their full moon in March by this name, owing to earthworms coming out of the thawing soil at this time of year.

Equinox, well that’s happening today. We only have two equinoxes per year, and they always occur around March 20th, and again 6 months later in September. For the Northern Hemisphere, the March equinox is called the Vernal or Spring Equinox, and denotes the astronomical beginning of Spring, while it starts Fall in the Southern Hemisphere. The September equinox is called the Autumnal or Fall Equinox.

But what is an Equinox? According to Wikipedia, equinox occurs at “the instant of time when the plane (extended indefinitely in all directions) of Earth’s equator passes through the center of the Sun”. Or in other words, when the center of the Sun is directly above the equator.

The two equinoxes are when the day and night are the same length (not exactly at the same moment as the Equinox, but pretty close). The equinoxes are also the only times of year that both the northern and southern hemisphere receive the same amount of light from the Sun.

This March Supermoon is the last full moon supermoon of this year, after having them in January and February as well (however, we have three supermoon New moons in August and September). The February one was the closest and brightest, but this one is unique. It is very rare for the supermoon to happen within a day of the equinox. It won’t happen again until 2030.

Owing to the momentous occasion of a Super Worm Equinox Moon happening today / tomorrow, I have deferred a description of the Moon’s seas and craters until Part 3 of this series.

Happy moon observing! Because you’re only going to see the brightest stars right now, skies permitting. If it’s too cloudy, there’s a link on the first reference, the National Geographic article below where you can watch it online.

Have a great day, and Happy Spring (or Fall, if you’re reading this from south of the Equator)!

Previous in series: Observing the Moon, Part 1: Appearance and Phases

References:

Fazekas, Andrew. (2019, March 19). See the first supermoon on the spring equinox in 19 years. Retrieved from https://www.nationalgeographic.com/science/2019/03/see-first-super-worm-moon-on-spring-equinox-in-19-years/.

McClure, Bruce, and Deborah Byrd. (2019, January 1). How many supermoons in 2019? Retrieved from https://earthsky.org/human-world/what-is-a-supermoon.

Wikipedia. (2019, March 20). Equinox. Retrieved from https://en.wikipedia.org/wiki/Equinox.

Wikipedia. (2019, March 14). Supermoon. Retrieved from https://en.wikipedia.org/wiki/Supermoon.

Wikipedia. (2019, February 22). Syzygy (astronomy). Retrieved from https://en.wikipedia.org/wiki/Syzygy_(astronomy).

Zodiac Constellation # 2: Cancer

By Peter Forrester | March 9, 2019

Next in our series of Zodiac Constellations is Cancer, the crab. In case you’re wondering, cancer is Latin for crab, and the disease is named after the crab, rather than the other way around.

Cancer is just to the left of Gemini. It is visible in the early evening in the eastern sky. However, it is the second dimmest of the 12 zodiac constellations. Its brightest star, Beta Cancri, only has an apparent magnitude of 3.5, and there is only one other star that is brighter than 4th magnitude. So you will need a clear moonless sky and be removed from city lights in order to see it. This is the best month to see it, around 9 pm. The Sun is located in Cancer between July 20 and August 9, although astrologers will use other dates for their sign of the zodiac called Cancer.

Just to the left of Cancer is another bright constellation, Leo the Lion. So the best way to find Cancer is to look in between Leo and Gemini. Look for a shape somewhat like an upside-down Y. The points are often identified as the pincers of a crab, but it has been described as various other creatures by ancient societies.

Ten stars in Cancer are known to have planets. One of them, called 55 Cancri, has 5 known planets – one a bit bigger than Earth, and the other 4 being gas giants. One of these gas giants is in the “habitable” zone where, based on its distance from the star, liquid water could exist and therefore life similar to what we have on Earth.

Another prominent object in Cancer is an “open cluster” of stars called Praesepe (Latin for manger), also known as the Beehive Cluster. It is located about 600 light-years from Earth, but is still one of the closest open clusters, defined as “a group of up to a few thousands stars that were formed from the same giant molecular cloud and have roughly the same age”.

Praesepe has an apparent magnitude of 3.7, very similar to Beta Cancri. The name comes from the ancient Greeks and Romans, who saw it as a manger out of which two donkeys were eating. This cluster was one of the first things Galileo Galilei looked at with his telescope in 1609. He saw 40 stars in Praesepe, which just looks like a nebula or cloud to the naked eye (best time to observe it is from February to May). Three planets are now known to exist orbiting two Sun-like stars in the cluster.

Coming back to Earth, the Tropic of Cancer is named for the constellation. It is a line you will see on a globe, the northern edge of a band around the middle of the planet known as the Tropics. It is about 23.5 degrees north of the Equator, and the line is the furthest north where the Sun can be directly overhead. Hawaii is located just south of this line (except for the many uninhabited islands at the northwest end of the island chain). The line is called after the constellation Cancer because the time the Sun is overhead is during the summer solstice (June 20), during which the Sun used to be located in Cancer (it is now in Taurus, because of a process called “precession of the equinoxes” or “axial precession”). The southern edge of the Tropics is the Tropic of Capricorn, which is the same distance south of the Equator.

I wish you all the best in your continued effort to admire these amazing objects in the sky above you. And soon it will be warm enough that you actually want to go out there at night. By the way, don’t forget to turn your clocks ahead tonight or in the morning for our annual tradition called Daylight Savings Time (at least for most of the United States).

Previous in series: Zodiac Constellation #1: Gemini

References:

Wikipedia. (2019, January 11). Axial precession. Retrieved from https://en.wikipedia.org/wiki/Axial_precession.

Wikipedia. (2019, February 14). Beehive Cluster. Retrieved from https://en.wikipedia.org/wiki/Beehive_Cluster.

Wikipedia. (2019, February 14). Cancer (constellation). Retrieved from https://en.wikipedia.org/wiki/Cancer_(constellation).

Wikipedia. (2019, March 6). Open cluster. Retrieved from https://en.wikipedia.org/wiki/Open_cluster.

Wikipedia. (2019, March 5). Tropic of Cancer. Retrieved from https://en.wikipedia.org/wiki/Tropic_of_Cancer.

Skies Over Milton, March Edition

By Peter Forrester | March 1, 2019

Greetings on this fine morning! Don’t forget Daylight Savings starts on Sunday, March 10.

Here are your March skywatching events, courtesy of skymaps.com:

Friday, March 1: Moon near Saturn, 2:00 PM, visible from Southwestern US.

Saturday, March 2: Moon near Venus, 6:00 PM (the planet is bright, magnitude -4.1).

Monday, March 4: Moon at apogee (farthest from Earth) at 6:00 AM.

Wednesday, March 6: New Moon at 11:04 AM.

Monday, March 11: Moon near Mars in the evening sky, 1:00 PM.

Thursday, March 14: First Quarter Moon, 6:26 AM.

Tuesday, March 19: Moon at perigee (closest to Earth) at 3:35 PM.

Wednesday, March 20: Vernal Equinox at 6:01 PM. An important event, this is the astronomical start of spring in the Northern Hemisphere, where the Sun crosses into the Northern Celestial Hemisphere. See the Wikipedia links below for more information.

Also on March 20, Full Moon at 9:42 PM.

Thursday, March 28: Last Quarter Moon at 12:10 AM.

Sunday, March 31: Mars 3 degrees from the Pleiades cluster at 3 AM.

Also there are other events I skipped involving the Moon being seen near other objects after the 11th of March. I really can’t exaggerate too much the value I’ve found from the free monthly downloads from skymaps.com. If you haven’t been to this site I highly recommend it.

One note on using skymaps – they give all their times in UTC (Coordinated Universal Time), also called Greenwich Mean Time (GMT) in English-speaking countries. This is the time in Greenwich, England. In the US Eastern Time Zone, our time is 5 hours before UTC when we are in Standard Time, and 4 hours before during Daylight Savings. I have been translating the times for you, but if you are looking at their information you will need to be able to convert the time yourself.

With all this, you ought to have another great month of looking at the stars. I wish you all the best, and looking forward to warmer weather with the start of spring this month!

Previous in series: Skies Over Milton, February Edition

References:

Thalassoudis, Kym. (2000-18). Skymaps. Retrieved March 1, 2019 from skymaps.com.

Wikipedia. (2019, February 27). Coordinated Universal Time. Retrieved from https://en.wikipedia.org/wiki/Coordinated_Universal_Time.

Wikipedia. (2019, February 27). Daylight saving time. Retrieved from https://en.wikipedia.org/wiki/Daylight_saving_time.

Wikipedia. (2019, February 28). Daylight saving time in the United States. Retrieved from https://en.wikipedia.org/wiki/Daylight_saving_time_in_the_United_States.

Wikipedia. (2019, February 19). March equinox. Retrieved from https://en.wikipedia.org/wiki/March_equinox.

Wikipedia. (2019, February 28). Pleiades. Retrieved from https://en.wikipedia.org/wiki/Pleiades.

 

Circumpolar Constellations: Cassiopeia

By Peter Forrester | February 23, 2019

Today I begin a series on the constellations that are close to the North Star. Constellations that never set from a person’s perspective are called “circumpolar”. They rotate once around Polaris every 24 hours but never go below the horizon. Which constellations are circumpolar depend on your latitude, or distance from the equator, but from northern latitudes between 40 and 50 degrees north, there are five constellations that are definitely circumpolar, with four of them having at least some fairly bright stars.

Milton’s latitude is 43º 24′ (43 degrees 24 minutes) North. If you imagine a circle sitting on the horizon, with the North Star, Polaris, at its center, then everything inside that circle is circumpolar. So I may extend this series out over more than just the first five parts.

I begin with the one called Cassiopeia (one of Ptolemy’s original 48 constellations in the 2nd Century AD), because it is currently high and easily visible in the early evening. The five brightest stars in this constellation form an “asterism” or group of stars with a very recognizable shape, which depending on its direction can be described as a funny “E”, “W”, “M”, or “3”.

If you imagine another circle around Polaris, this one with the Big Dipper on the edge, then Cassiopeia is also on this circle, across from the Big Dipper. In other words, it’s about the same distance away from Polaris as the dipper, but on the other side. So you will always find her in a northerly direction.

Cassiopeia was a vain queen in Greek mythology, who bragged that she and her daughter Andromeda were more beautiful than the Nereids, the daughters of the sea god Nereus. In anger, the god Poseidon punished her kingdom, and she and her husband were persuaded to sacrifice Andromeda to a sea creature Cetus, but she was fortunately rescued by the hero Perseus. Some depictions of Cassiopeia show her chained to a chair of a type once used in torture, which is said to be the gods’ final punishment.

The brightest star in Cassiopeia, Schedar, or α (Alpha) Cassiopeiae, has an apparent magnitude of 2.2. The γ (Gamma)  star sometimes brightens up to 1.6 but is normally around 2.3 in magnitude. Two of the three other stars in the “W” asterism are between 2.3 and 2.7 in magnitude. The dimmest of the five stars in the asterism has a magnitude of 3.3.

The Milky Way (what appears to be a long, thin cloud but is actually the edge of the disk of the galaxy) runs through Cassiopeia. Thus there are many “deep sky” objects such as star clusters and nebulae, and two supernova remnants (including a famous supernova from the year 1572). There are also several galaxies within Cassiopeia. Some of these deep-sky objects can be seen with the naked eye, but generally it takes a telescope to get a good view.

Cassiopeia was one of the first constellations I learned to identify as a teenager because it is so bright and always so close to the North Star. I hope you will take the time to look up and see if you can find it, and happy stargazing!

References:

The Urban Astronomer. (2008, December 17). Circumpolar Stars. Retrieved from http://urbanastronomer.blogspot.com/2008/12/circumpolar-stars.html.

Wikipedia. (2019, February 12). Cassiopeia (constellation). Retrieved from https://en.wikipedia.org/wiki/Cassiopeia_(constellation) on February 19, 2019.

Wikipedia. (2019, January 22). Cassiopeia of Ethiopia. Retrieved from https://en.wikipedia.org/wiki/Cassiopeia_of_Ethiopia on February 19, 2019.

Wikipedia. (2018, January 28). Circumpolar constellation. Retrieved from https://en.wikipedia.org/wiki/Circumpolar_constellation on February 19, 2019.

Wikipedia. (2019, February 11). Latitude. Retrieved from https://en.wikipedia.org/wiki/Latitude on February 19, 2019

Bright Stars: Sirius

By Peter Forrester | February 13, 2019

The brightest star in the night sky, as seen from Earth, is called Sirius. It is the second brightest overall (obviously the Sun is the brightest star we can see).

Sirius is larger than the Sun, but weak and relatively dim compared to many other stars, but it is so close to the Sun (8.6 light years) that its apparent magnitude (-1.46) is almost twice as bright as any other star. It has an absolute magnitude of 1.42.

Being so bright, Sirius was important in the mythology of many ancient cultures. For example, its appearance in the sky shortly before sunrise (its “heliacal rising”) occurred just before the summer flooding in ancient Egypt and was an important omen in their religion. Their civil calendar was originally based on the return of Sirius, but wandered off within 4 years. However, they continued to observe its return and discovered a cycle that became part of the Julian and Alexandrian calendars.

The Ancient Greeks associated Sirius with hot weather, men becoming weak, and other bad consequences, terming the time right after its return “dog days” because of its constellation, Canis Major. Its association with dogs also concerned the way dogs pant in hot weather, which made some ancient people fear they might have a disease, even in some cases rabies. For more on the mythologies associated with Sirius, see the Wikipedia link below.

Sirius is in Canis Major, or the Great Dog, which is just to the left of Orion as seen in the Northern Hemisphere. Being the brightest star in this constellation, its abbreviation is α CMa. Canis Major is often depicted as a dog of Orion who is helping him hunt the Bull, Taurus.

Sirius is actually made up of two separate stars, Sirius A and Sirius B. Sirius A has an absolute magnitude of +1.42, while Sirius B (nicknamed “the Pup”) is much, much dimmer at +11.18. The distance between them is about 20 AU, or about the distance of Uranus from the Sun. 1 Astronomical Unit (AU), the distance between the Earth and the Sun, is about 93 million miles. Sirius A is blue-white, while Sirius B is a white dwarf, the second one ever discovered.

The existence of a second star was first hypothesized in 1844, and observed in 1862. A third companion star has been suggested to explain small changes in the movement of the star system but its existence has never been verified.

Sirius is one of the three stars in a shape called the “Winter Triangle”, along with Procyon in Canis Minor, and Betelgeuse in Orion. Those who know the constellation Orion should be able to find Sirius easily. You just follow the belt down to the left, the star is about 8 times the width of the belt away from it. These directions will be opposite in the Southern Hemisphere.

There are four planets brighter than Sirius (two of them, Jupiter and Venus, are always brighter when visible, with Mercury and Mars being brighter some of the time). Since it is known to be the brightest night-time star, knowing its location can help you identify planets in the sky.

It is possible to see Sirius in daylight, though there are several conditions that have to be met, such as the sky being clear, the Sun being low on the horizon, Sirius being overhead, and the observer being at a high altitude. These conditions are met more easily in the Southern Hemisphere, since the star gets higher in the sky there. Sirius is gradually moving to the south and will no longer be visible in northern or central Europe in about 7,000 years.

Sirius contains 2 of the 8 nearest stars to our solar system, and is the fifth closest stellar system to us. The Voyager 2 spacecraft launched in 1977 is expected to pass about 4 light years from Sirius in about 300,000 years. No planets have been detected in the Sirius system, and because of differences in the stars, the conditions for life being met would be much more difficult. In particular, Sirius B used to be a red giant and thus would have swallowed up any planets. Also Sirius A is much brighter than the Sun and thus habitable planets would have to be much further away than the Earth is from the Sun. Sirius A is also much younger than the Sun and thus there would have been much less time for life to have evolved on any planet there.

There are a couple of historical controversies concerning Sirius. The first is about the color of the star, which ancient authors described as red, but the star is now known to be white to blue-white in color (various colors can be seen in its twinkling, because of effects of the light passing through Earth’s atmosphere).

The second controversy concerns a native tribe in Mali, Africa, which has been claimed to have known about the second star before Western astronomers (they also said there was a third star with a planet). But the accounts have been disputed and it seems the author who wrote about it in 1938 may have been the one to tell them, or they may have learned about it from a French expedition to view an eclipse in 1893.

This is the best month of the year to observe Sirius in the early evening, although it can also be seen in the early morning during summer. Happy skywatching!

References:

Byrd, Deborah. (2019, February 7). Sirius is Dog Star and brightest star. Retrieved from https://earthsky.org/brightest-stars/sirius-the-brightest-star on February 13, 2019.

Howell, Elizabeth. (2018, October 24). Sirius: Brightest Star in Earth’s Night Sky. Retrieved from https://www.space.com/21702-sirius-brightest-star.html on February 13, 2019.

Wikipedia. (2018, December 31). Heliacal rising. Retrieved from https://en.wikipedia.org/wiki/Heliacal_rising.

Wikipedia. (2019, February 12). Sirius. Retrieved from https://en.wikipedia.org/wiki/Sirius.

Zodiac Constellation #1: Gemini

By Peter Forrester | February 6, 2019

Greetings, stargazers!

In case you’re wondering about my choice of constellations, I pointed out in the article about the Zodiac that the constellations each have the Sun in their direction for about one month; although that month is off by a little bit from the traditional astrological dates. I therefore can’t write about it in its normal month because it can’t be seen then. I will be writing about a constellation that is visible in the east in the early evening, around 6 or 7 pm in US Eastern Time.

Gemini is Latin for “twins”, and indeed, the two brightest stars in Gemini are very similar in brightness, if not in detail. Castor and Pollux were twins from Greek mythology, hunters and later sailors on Jason’s Argo. They were said to have been placed together in the sky after one of them was killed. Oddly, they are also often said to have had different fathers, with one of the fathers being the god Zeus.

Pollux is the brightest star in Gemini, with an apparent magnitude of 1.14. It is an orange giant star about 34 light-years from Earth. Castor is just behind it at 1.58, but actually consists of SIX different stars, in three binary pairs. They are 52 light-years away, and appear to be a single blue-white star.

The brightest stars in each constellation are assigned Greek letters, with the brightest one usually being designated as Alpha (α), but Gemini is an exception, with Castor being α Geminorum, or in short form α Gem (you’ll often see this short form next to the stars on sky charts). Pollux, the brightest star, gets the next letter, Beta (β Geminorum or β Gem). After proceeding through all 24 letters of the Greek alphabet, the dimmer stars will be assigned numbers.

The remainder of the constellation principally consists of two lines of stars, one extending out to the right of each of the bright stars (in the northern hemisphere). There are 85 stars in Gemini that are visible without using a telescope. Four of the stars are brighter than 3.00. Eight of the stars are known to have planets, one of them being Pollux.

In drawings of the constellation, Castor and Pollux are the heads of the twins, with the parallel line going down along towards their feet at the other end. Their feet are pointed right at the constellation Orion.

Gemini is easy to find in the sky if you can identify Orion (February is the best month to see Gemini, so I recommend braving the cold). From northern latitudes, it appears just to the east (left) and slightly above Orion. If you make a line from the right side of Orion’s belt, or the right foot, and pass through the left shoulder (from your perspective), it will lead straight to Castor and Pollux.

Gemini is important in astronomical history: the planet Uranus and the former planet, now dwarf planet Pluto, were both discovered in Gemini, in 1781 and 1930, respectively. Much earlier, Aristotle wrote about the earliest recorded occasion of a planet occulting, or passing in front of a star. The planet Jupiter passed in front of a star in Gemini; it is believed that the star was the one called 1 Geminorum (not the 25th brightest – its number comes from a catalog that was done from west to east), and that the event occurred on 5 December, 337 BC.

Next in series: Zodiac Constellation # 2: Cancer

References:

Encyclopaedia Britannica. (2009, February 18). Castor (star). Retrieved from https://www.britannica.com/place/Castor-star.

Wikipedia. (2018, July 27). 1 Geminorum. Retrieved from https://en.wikipedia.org/wiki/1_Geminorum.

Wikipedia. (2019, January 10). Castor (star). Retrieved from https://en.wikipedia.org/wiki/Castor_(star).

Wikipedia. (2019, January 29). Gemini (constellation). Retrieved from https://en.wikipedia.org/wiki/Gemini_(constellation).

Wikipedia. (2019, January 2). Pollux (star). Retrieved from https://en.wikipedia.org/wiki/Pollux_(star).

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