The Big Dipper in Yellowstone, by Alex Conu, Norway

image
Created for the OAE

Caption: First place in the 2021 IAU OAE Astrophotography Contest, category Wide star fields. This image shows one of the most prominent and well-known asterisms of the Northern Hemisphere – the Big Dipper or the Plough. This asterism is part of the constellation from Greek mythology – Ursa Major (the Great Bear). The Big Dipper comprises seven (eight) stars extending from the center to the right of the image. The four stars that form the “cup” of the dipper are in the shape of a trapezium just above the tallest tree towards the right of the image. These stars are Dubhe (top right), Merak (bottom right), Megrez (top left) and Phecda (bottom right). The three (four) stars that form the handle are to the left to trapezium (from right to left: Alioth, Mizar and Alkaid). Looking closely at Mizar, it is possible to see a smaller star to the top left and “touching” Mizar. This is Alcor, and with Mizar they make up the unaided-eye double-star system. However, very careful measurements have provided evidence that Mizar is in fact a quadruple system, and Alcor is a binary system. Although the names of the stars are derived from the Arabic names for the stars, different cultures have their own names for the stars. In various cultures around the world, this asterism is associated with different objects, and furthermore, some indigenous cultures associate stories with individual stars. Constellations in addition to encompassing stories and myths of various cultures, are important navigation “tools”. The stars Dubhe and Merak, can be used to find the Pole (North) Star – Polaris (not seen in this image). Given its relationship to the Northern Hemisphere and being a circumpolar constellation (never setting below the horizon), the Big Dipper and Polaris are used on the flag of Alaska. It is important to note that although the stars (except for the multiple star systems of Mizar and Alcor) in constellations appear to be “next” to each other, in reality the stars are at various distances from Earth and from each other.
Credit: Alex Conu/IAU OAE

Glossary Terms: Asterism
Categories: Naked Eye Astronomy , Stars

License: Creative Commons Attribution 4.0 International (CC BY 4.0) Creative Commons Attribution 4.0 International (CC BY 4.0) icons

This file on Zenodo ( image 11.24 MB)

Neowise's metamorphosis, by Tomáš Slovinský and Petr Horálek, Slovakia

image
Created for the OAE

Caption: First place in the 2021 IAU OAE Astrophotography Contest, category Comets. This image uses the chronophotography technique to capture the evolution of the comet C/2020 F3 (Neowise) over time, as it became visible in the northern skies in July 2020. Orbits of comets are extremely elliptical, which means that during part of their orbit they get close to the Sun. As a comet approaches the Sun, it gets heated, releases gas and dust creating an envelope or coma around the nucleus. The solar wind and photons (particles of electromagnetic radiation) interact with the coma producing the cometary tail, which can be seen clearly in this image. The tail of a comet always points away from the Sun, and extends as much as tens of millions of kilometres. This tail has two parts: the relatively straight bluish gas (ion or plasma) tail, which is made up of charged particles interacting with the magnetic fields of the solar wind; and the whitish dust tail compose of very small dust particles that are pushed by the radiation pressure from the Sun into a curve due to their slower speeds. Two regions in the Solar System are often associated with being “storehouses” of comets: the Kuiper Belt and the Oort Cloud. Comets with periods up to about two hundred years come from the Kuiper belt, a reservoir of cometary nuclei material with a disk-like shape located beyond Neptune. Longer period comets come from the Oort cloud, another huge reservoir of icy objects, with a spherical shape surrounding the Solar System. The outer limit of the Oort Cloud is not known as yet, but it could be as much as 10 thousand times the Sun-Earth distance, or even more. Due to gravitational disturbances, some of these cometary nuclei might be ejected towards the inner regions of the Solar System, sometimes approaching the Earth, offering some of the most spectacular views of a celestial body. The image also shows some prominent constellations and asterisms like the Big and Little Dippers, and also the North (Pole) Star – Polaris.
Credit: Tomáš Slovinský and Petr Horálek/IAU OAE

Glossary Terms: Comet
Categories: Naked Eye Astronomy , Solar System

License: Creative Commons Attribution 4.0 International (CC BY 4.0) Creative Commons Attribution 4.0 International (CC BY 4.0) icons

This file on Zenodo ( image 19.53 MB)