In our December Night Sky Notes, we mentioned that the Orion constellation has a distinct hourglass shape that makes it easy to spot in the night sky. But what if we told you that this is not the complete constellation, but rather, an asterism?
An asterism is a pattern of stars
in the night sky, forming shapes that make picking out constellations easy.
Cultures throughout history have created these patterns as part of
storytelling, honoring ancestors, and timekeeping. Orion’s hourglass is just one
of many examples of this, but did you know Orion’s brightest knee is part of
another asterism that spans six constellations, weaving together the Winter
night sky? Many asterisms feature bright stars that are easily visible to the
naked eye. Identify these key stars, and then connect the dots to reveal the
shape.
Asterisms Through the Seasons
Try looking for these asterisms this season and beyond:
- Winter Circle – this asterism, also known as the Winter Hexagon, makes up a large portion of the Winter sky using stars Rigel, Aldebaran, Capella, Pollux, Procyon, and Sirius as its points. Similarly, the Winter Triangle can be found using Procyon, Sirius, and Betelgeuse as points. Orion’s Belt is also considered an asterism.
- Diamond of Virgo – this springtime asterism consists of the following stars: Arcturus, in the constellation Boötes; Cor Caroli, in Canes Venatici; Denebola in Leo, and Spica in Virgo. Sparkling at the center of this diamond is the bright cluster Coma Berenices, or Bernice's Hair – an ancient asterism turned constellation!
- Summer Triangle – as the nights warm up, the Summer Triangle dominates the heavens. Comprising the bright stars Vega in Lyra, Deneb in Cygnus, and Altair in Aquila, this prominent asterism is the inspiration behind the cultural festival Tanabata. Also found is Cygnus the Swan, which makes up the Northern Cross asterism.
- Great Square of Pegasus – by Autumn, the Great Square of Pegasus can be seen. This square-shaped asterism takes up a large portion of the sky, and consists of the stars: Scheat, Alpheratz, Markab and Algenib.
This image shows the region around the Hyades star
cluster, the nearest open cluster to us. The Hyades cluster is very
well-studied due to its location, but previous searches for planets have
produced only one. A new study led by Jay Farihi of the University of
Cambridge, UK, has now found the atmospheres of two burnt-out stars in this
cluster — known as white dwarfs — to be “polluted” by rocky debris circling the
star. Inset, the locations of these white dwarf stars are indicated — stars
known as WD 0421+162, and WD 0431+126.
NASA, ESA, STScI, and Z. Levay (STScI)
Tracing these outlines can guide
you to objects like galaxies and star clusters. The Hyades, for example, is an
open star cluster in the Taurus constellation with evidence of rocky planetary debris. In 2013, Hubble Space Telescope’s Cosmic Origins Spectrograph was responsible for breaking down light into
individual components. This observation detected low levels of carbon and
silicon – a major chemical for planetary bodies. The Hyades can be found just
outside the Winter Circle and is a favorite of both amateur and professional
astronomers alike.
How to Spot Asterisms¨
- Use Star Maps and Star
Apps – Using star maps or stargazing apps
can help familiarize yourself with the constellations and asterisms of the
night sky.
- Get Familiar with
Constellations –
Learning the major constellations and their broader shapes visible each
season will make spotting asterisms easier.
- Use Celestial Landmarks –Orient yourself by using bright
stars, or recognizable constellations. This will help you navigate the
night sky and pinpoint specific asterisms. Vega in the Lyra constellation
is a great example of this.
Learn more about how to stay warm while observing this Winter with our upcoming mid-month article on the Night Sky Network page through NASA's website!
by Kat Troche of the Astronomical Society of the Pacific
Source: January's Night Sky Notes: Connecting the ‘Dots’ with Asterisms - NASA Science
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