Our Night Sky Episode 14 features the season’s brightest star and a beautiful morning lineup for the month of May.
Looking high in the sky – slightly East, early in the evening, early in the month, and straight overhead as the evening and month progresses – you’ll find the very bright, orange-tinted Arcturus, constellation Bootes’ brightest star. If you’re familiar with the Big Dipper, you can follow the arc of the dipper’s handle directly to Arcturus.
Look more closely, and you’ll see that Arcturus sits as the bottom point of a six-starred kite, with four additional stars trailing beneath Arcturus as the kite’s tail. This kite, with its additional “arm” stars, outlines the constellation Bootes, a herdsman in ancient cultures.
Arcturus is a red-giant star 113 times more luminous than our Sun. It is our sky’s 3rd brightest star and is located some 37 light years away. A light year is the distance that light travels in one year and is equal to almost 6 trillion miles. To compare, using this light-travel time scale, Pluto, at about 4 billion miles, is just 5 light hours away.
Now, here’s a challenge. Using binoculars, look just ten degrees (about the width of your fist at arm’s length) to Arcturus’ NW. Take your time scanning the region and you’ll run across a fuzzy round patch. That is the globular cluster M3 – a gravitationally bound collection of about half-a-million stars located in Bootes’ neighboring constellation, Canes Venatici.
Five planets grace the morning sky the entire month of May. Venus and Mars rise as a pair in the hours just before sunrise on your East horizon. Venus appears as a bright star – Mars has an orange hue. Jupiter rises on your SE horizon about an hour before Venus and Mars. See if you can spot Jupiter’s four Galilean moons with your binoculars. Faint Neptune is there, as well, slightly E of Jupiter, as is the equally faint Uranus, in that diagonal region between Jupiter and Venus. Luna highlights the scene midmonth, posing with Jupiter on the 16th and 17th and as a crescent with Venus & Mars on the 21st.
You can click here for a printable star chart centered on Bootes and the Big Dipper. The software, Touring the Universe Through Binoculars Atlas, is free to download from TUBA Software by Phil Harrington and Dean Williams.
Bootes: Bootes is a northern hemisphere constellation positioned between Draco and Ursa Major to the north, Canes Venatici and to the west, Virgo to the south, and Hercules, Corona Borealis, and Serpens Caput to the east. The globular cluster, NGC 5466, and a large number of double-stars can be found in Bootes, offering an enjoyable challenge for binoculars observing. Bootes is also home to the Bootes Void, a vastly empty region of space located 700-million light years away and spanning some 300-million light years across.
Arcturus: Arcturus is an orange subgiant K star with temperatures ranging around 3600 to 4900 C. Not only is it Bootes’ alpha star, Arcturus is the second brightest star in the northern hemisphere and was one of the first stars to have its proper motion measured. While this star has nearly twenty times the radius of our Sun, it has only about 1.5 times the mass. This is because most red-giant stars are really, originally, sun-like stars that have evolved to expand their outer layers, with much of their size being simply bloated atmosphere.
M3: M3 is a gravitationally bound collection of about half-a-million stars spanning across a 180 LY region. This cluster resides some 34,000 LY away in the constellation Canes Venatici, looking towards the center of the Milky Way. Though better seen with binoculars, and best seen with a telescope, M3 is actually visible to the unaided eye in darker skies. Globular clusters, like M3, are among the oldest known objects in our galaxy. They orbit the galactic center as a halo above the galactic plane, following a path that often takes them beyond the outer regions of the galaxy and back in again.
Backyard Observing: 1) Choose an area that is both safe and dark. Your house, sheds, and even trees can help to shield against neighboring lights. 2) Carry a flashlight to avoid accidents, especially with younger children. You can cover the end of your flashlight with red cellophane, or even purchase a specially-filtered flashlight from your local department store, to avoid flooding your eyes with light. 3) Make yourself comfortable and permit your eyes to adapt to the darkness. You’ll find that the longer you’re outside, the more stars you’ll begin to see. 4) Be patient – give yourself time plenty of time to become familiar with the sky. See if you can recognize star patterns and compare them with a planisphere to learn which constellations are where. 5) Use special care when observing near the setting or rising sun, and never look directly at the sun without solar-filtered binoculars or telescopes.