Astronomy For Change

Betelgeuse, the prominent red supergiant star marking Orion's right shoulder has unexpectedly brightened. A departure from the 2019 dimming, this brightening has sparked a flurry of speculation and a number of studies reigniting speculation of an imminent supernova.

The star has long exhausted the compliment of hydrogen fuel in its core and has been burning helium, producing carbon and oxygen. Recent observations show that the star is brightening again after a period of dimming, leading to speculation that a supernova is imminent.

Historically, several significant supernovae have been visible in the night sky, including SN 1054, which created the Crab Nebula and was observed by Chinese and Japanese astronomers. If Betelgeuse were to go supernova, its proximity to Earth means that it would be visible in the night sky for several weeks or months, providing insights into the physics of supernovae and furthering our understanding of the universe. Regardless of the outcome, the increased interest in Betelgeuse highlights the incredible beauty and wonder of our universe.

Betelgeuse, red star, Orion, brightness increase, supernova explosion, red giant star, largest stars in the universe, dimming, Crab Nebula, visible in the night sky, explosion, insights into the physics of supernovae, universe

Episode image credit: R.S. Wright 

Today we look at the sky for the week beginning Sunday, July 25th. The sky has changed somewhat since last week. In the morning, Mercury is in Cancer with the sun and lost in the solar glare before sunrise. The evening sky sees Venus remaining prominently placed with Mars setting earlier than last week.

Scorpio with red supergiant Antares, the heart of the Scorpion, is on the meridian at 9:20 PM, EDT with Sagittarius due east and prominently placed by midnight. As they have been for the previous 3 weeks, Jupiter and Saturn are both well placed by 10:30 PM EDT with the waning gibbous moon in Pisces and rising at 11:00 PM on the evening of July 27th. The ethereal majesty of the summer milky way and galactic center, 25,000 light years distant, join Sagittarius on the meridian.  

As we did last week, the great Summer Triangle, the hallmark of the summer sky in the Northern Hemisphere, is well placed midway up in the east for North America. Following the Milky Way northward from the galactic center we find this asterism, consisting of brilliant, blue-white Vega in Lyra, the Harp, blue-white Supergiant Deneb in Cygnus and clear-white Altair in Aquila, the Eagle. 

In this week’s edition of The Sky Tonight, we’d like to highlight 3 favorites of the summer sky, 2 globular clusters and one galactic cluster.

Globular Clusters contain some of the oldest stars in the universe, some of the first stars formed after recombination. It is a widely accepted that when the first stars formed in our universe approximately 13 billion years ago, they quickly came together to form globular clusters. These clusters then coalesced with others to form the first galaxies, a process that continues to this day, galaxies growing through mergers and evolving over time, ever since. For this reason, we’ve long suspected that the oldest stars in the universe populate globular clusters. 

All constituent stars of a globular cluster formed at the same time and from the same cloud of gas and dust and thus constitute a ‘single stellar population’. This singular aspect of globular clusters provides a unique insight into stellar formation and evolution. Additionally, since many constituent stars date to the earliest epoch following recombination, careful analysis of their spectra and composition provides additional confirmation of the age of the universe of 13.8 billion years.

Stars in these clusters, compared to the hot, young stars in galactic clusters such as M-11, the Wild Duck cluster, the third of 3 objects of interest in this episode, are among the oldest stars in the universe.

The first globular cluster we’re going to discuss is Messier (M)-4.

70 ly wide and over ten times the distance to Antares at 7,200 Ly and immediately to its west, is the globular star cluster Messier-4.

Although visible in a pair of binoculars as a soft, fuzzy globe, a telescope is required to reveal its true nature as an agglomeration of over 60,000 stars, all gravitationally bound together. 

The next object of interest is the globular star cluster Messier-22

Located at 10,600 ly in the ‘Teapot’ of Sagittarius, also known as ‘The Crackerjack Cluster’ and similar to Messier-4, is Messier-22. Although this cluster is further away than M-4, it’s brighter as M-4 is located behind the Rho Ophiuchi complex, a region replete with gas and dust.

The third and final object is M-11, the Wild Duck cluster, named as such since it appears a flock of wild ducks. The cluster is easily observed in a pair of 10x50 binoculars and beautifully resolved in a 15 cm (6” telescope).

Uranus, in Aries, requiring a telescope and flanking the 3rd quarter moon to the east rises at midnight tomorrow, July 31st. The moon, with Uranus (requiring a telescope) is beautifully placed at 3:00 AM, EDT with the Pleiades high in the East at 3:00 AM, EDT at 12:45 AM.

With this edition of the sky tonight, the sky has changed slightly since last week. Today we look at the sky for the week beginning Sunday, July 18th.

Sunday, July 18th, we have brilliant Venus and ruddy red Mars still well placed in the Southwest sky and setting at 9:50 PM, EDT, following the sun as it sets at 8:26 PM, EDT. As the two planets set, red supergiant Antares, the heart of the Scorpion, has passed the meridian with Sagittarius becoming well placed to the east on the meridian.

The waxing gibbous moon is east of Spica and sets at 1:00 AM, EDT, allowing another 4 hours to admire and observe the ethereal majesty of the summer milky way and galactic center, 25,000 light years distant, under a dark, moonless sky.

Continuing east, the great Summer Triangle, the hallmark of the summer sky in the Northern Hemisphere, is well placed midway up in the east for North America. Following the Milky Way northward from the galactic center we find this asterism, consisting of brilliant, blue-white Vega in Lyra, the Harp, blue-white Supergiant Deneb in Cygnus and clear-white Altair in Aquila, the Eagle.

Just to the north of Deneb and visible in a good pair of binoculars on a clear, dark moonless night is the “North America” nebula, an H-II region or emission nebula shaped like the North American Continent and excited to shine by the UV ionizing radiation from a hot, luminous O-B class binary star close by.

[These types of stars live short, die young and are the brightest, most luminous, most massive in the Morgan-Keenan stellar classification system with many of them ending their short lives in spectacular fashion as Type-II Core Collapse supernovae].

We should also mention Sagitta the arrow and Vulpecula, the little fox, identified only by to starsboth to the east of Alberio, a beautiful blue-white and “gold” binary star, the head of Cygnus, its second brightest star and member of the “Northern Cross” asterism.

To the south and east of the North America nebula and east of Aljanah in the “Northern Cross” is the Veil Nebula, subtle and faint and requiring a respectable pair of binoculars or a richest-field telescope on a clear, dark, moonless night is a supernova remnant, still expanding from the stellar explosion over 10,000 years ago.

Rising at 9:15 and 10:00 PM, EDT, respectively, Saturn and Jupiter are still low in the Southeast and, as it was last week and following the Summer Triangle, Jupiter and Neptune are in Aquarius with Saturn in Capricorn.

The location on the sky of these outer planets hasn’t changed much in the intervening week as their orbital periods, dependent on their distance from the sun, are measured in multiple earth years, with Jupiter completing one orbit in 12 years, Saturn in 30 and Neptune completing one orbit in 165 years.

Uranus, rising at 12:45 AM, EDT is in Aries and flanked later on close to 3:00 AM by the shimmering Pleiades or the Seven Sisters to the Northeast.

Continuing further east, Mercury precedes the sun, rising at 4:30 AM, EDT on the morning of Monday, July 19th, 10 minutes later than last week, with red giant Aldebaran, the heart of Taurus, to the east and south.

Zooming in on Mercury, we take note of its phase, a phenomenon not unlike that of our own moon, caused by the relative location of the observer, the object and the source of the illumination, in both cases, the sun.

Since last week, the phase has waxed to a more “gibbous phase” as the planet moves closer to superior conjunction, the point where it is 180 degrees from our point of view “behind” the sun. With sunrise just over an hour later at 5:40 AM on the morning of July 19th, Mercury is well placed for early risers with over an hour of visibility.

Note: with the exception of the Earth and Pluto, all the planets of the solar system are visible during this time period and were discussed in this podcast.

Sunday, July 4th (Independence Day in the US), we have brilliant Venus and ruddy red Mars in Cancer following the sun at sunset. By 9:30 PM, EDT, these planets have set with Regulus, the heart of Leo, setting by 10:00 PM.

Pivoting east, we find blue-white Spica, the brightest star in Virgo, high in the southwest with the red supergiant Antares of Scorpio further east and approaching the meridian at 9:30. Sagittarius is low in the southeast and, along with Scorpio, will become more prominent as the short nights of summer continue thru July and into August.

Continuing east, we see the great Summer Triangle, well placed midway up in the east for North America. This asterism, consisting of brilliant, blue-white Vega in Lyra, the Harp, blue-white Supergiant Deneb in Cygnus and clear-white Altair in Aquila, the Eagle, the Summer Triangle is the Hallmark of the summer sky in the Northern Hemisphere.

Following the Summer Triangle, low in the Southeast and rising after midnight (July 5th), Jupiter is in Aquarius and Saturn is in Capricorn. Pivoting further east, rising after 4:00 AM, EDT, the slim waning crescent moon, 4 days before new moon on July 9th is between Taurus and Aries and beautifully placed just Southeast of the Pleiades.

Continuing further east, Mercury precedes the sun at 4:40 AM with sunrise less than an hour later at 5:35 AM on the morning of July 5th, 2021, well placed for early risers with almost an hour of visibility before sunrise.

On 3 October of this year, in what the prestigious Royal Swedish Academy described simply as “a discovery that shook the world”, three Americans were awarded this year’s Nobel Prize in Physics “for decisive contributions to the LIGO detector and the observation of gravitational waves”, waves famously predicted by Albert Einstein’s General Theory of Relativity 102 years ago at the end of last month.