Astronomy Daybook: The Night Sky Day by Day
A record of the night sky
Our Astronomy Daybook is a perpetual chart of the night sky. There is one entry for every day of the year. Each day gives you where the Sun falls among the constellations, the highlights of tonight’s night sky, a deep-sky object observable with binoculars or telescope, a featured star with its distance from Earth and its history, and, lastly, two moments from the history of astronomy tied to the date. This page includes events for both the Northern and Southern hemispheres. Search for today, your birthday, or any other special day.
The Flank of the Horse
The Sun is in Virgo at roughly 0° declination, effectively on the celestial equator. Day length is very close to 12 hours everywhere; the equinox is about one week away.
The Great Square of Pegasus transits the meridian around midnight this week, making the coming nights ideal for surveying Pegasus, Andromeda, and the surrounding autumn constellations from northern latitudes. No major annual meteor shower peaks today.
NGC 7331, spiral Galaxy, Pegasus. A large tilted spiral about 40 million light-years away, NGC 7331 is often compared to the Milky Way in size and structure. It is well-placed for Northern Hemisphere observers; low but accessible from mid-southern latitudes.
Algenib (γ Peg) is a hot blue subgiant of spectral type B2IV, about 391 light-years away, one of the most physically energetic of the four Great Square stars. It is also a Beta Cephei variable, pulsating with a period of just 3.64 hours and a luminosity variation so small it was detected only by precise photometry.
Algenib is the quietest corner of the Square to the eye, but photometrically it is pulsing in three-hour cycles, the sky keeps secrets that numbers reveal.
What you’re looking at
Each day’s entry looks at the special astronomical events that are happening that night.
Date Title: A short name for the day drawn from whatever is most notable in the sky that evening, a constellation at its peak, stars crossing the meridian, a shower building toward its maximum visibility.
Sun Position: Where the Sun sits in the sky on this date: which constellation it occupies, how high or low its arc runs, and what that means for the length of your day and night. This section is written for both hemispheres because the sky looks different depending on which side of the equator you’re standing on, and many astronomy writing omits that.
Sky Highlight: The most interesting thing happening overhead tonight: meteor showers, the Milky Way, and other noteworthy stellar events. If nothing dramatic is happening, we note it and then point you toward something quieter.
Deep Sky Object: One object beyond our solar system worth knowing about on this date, a star cluster, a nebula, or a galaxy. These are things you can find with binoculars or a small telescope, and the entry tells you what you’re actually looking at, not just the catalog number.
Featured Star: One star with its name, distance, physical character, and an interesting fact. Many stars have long histories: in navigation, in mythology, and in science.
This Day in Astronomy: Two historical events connected to this date: a discovery, a launch, a first observation, a person born, or a mission completed. The history of astronomy is the history of humans trying to understand where they are, and this section keeps that thread running through the year.
Closing Line: One sentence to close your night on a poetic note.
A note on hemispheres
Most sky guides are written from the Northern Hemisphere and don’t include the Southern Hemisphere. This one tries to speak for both. Where what you see depends on where you are, the entry says so.
A note on years
This astronomy daybook is accurate year after year. The Sun’s position on June 1st, the stars overhead in October, the meteor showers of August, these repeat with enough consistency that a perpetual almanac holds. Individual historical dates are fixed. The sky itself shifts slowly over centuries, but nothing in this almanac will change drastically in your lifetime.