SKY GUIDE: This map represents the night sky as it appears over Maine during July. The stars are shown as they appear at 10:30 p.m. early in the month, at 9:30 p.m. at midmonth, and at 8:30 p.m. at month’s end. Mercury is shown at its midmonth position. To use the map, hold it vertically and turn it so that the direction you are facing is at the bottom. Sky Chart prepared by Seth Lockman
The month of July is named after Julius Caesar and was once the fifth month of the year when March was the first month. July always marks the first full month of summer for us in the northern hemisphere and the nights remain quite short.
There are a few interesting highlights this month that will be worth looking for even with the short nights, potential heat and bugs that will try to diminish your experience of the celestial beauty of the night sky. However, there no more epic celestial adventures like the epic April 8 total solar eclipse and the May 10 fantastic display of the northern lights – visible all the way down to parts of Texas and Florida – scheduled for this month.
Some events are accurately and mathematically predictable for over 100,000 years into the future, like all the different kinds of eclipses. Some events are just more likely to occur at certain times, like northern lights when the sun is more active. Then there are even less predictable events, like when a new comet might appear and become visible to the naked eye. Then there are extremely short-term unpredictable events, like any given bright and colorful fireball streaking through the sky. That could happen at any time through the night, but is more likely during a good meteor shower like the Perseids, Geminids, or Leonids.
Then you have another class of events that are predictable within a certain time frame like about half a year. We are looking for one of those right now with great anticipation which will be a once-in-a-lifetime opportunity for most of us. A star in Corona Borealis (or the Northern Crown, T Corona Borealis) nicknamed the “Blaze Star” is expected to get over 1,000 times brighter sometime between now and September. This is called a recurrent nova, is the brightest one in the entire sky, and undergoes this extreme brightening about every 80 years.
Discovered in 1866 by John Birmingham, this star has also been recorded to brighten so spectacularly four times already, in 1217, 1787, 1866, and 1946. Now we are ready for the fifth time. The physics is fairly simple, but still fascinating because of the huge scale involved and the other potential outcomes of a similar explosion. There is an extremely dense and small white dwarf, about the size of the earth which is being orbited by a red giant star many times larger than the sun about 50 million miles away from the white dwarf. The whole system is about 3,000 light years away in the constellation of Corona Borealis, now easily visible right next to Hercules and just south of the Big Dipper. It is a semicircular upside down crown of seven stars. The Blaze Star will appear just below the second star from the left of this crown.
A white dwarf by itself is already an expression of an interesting quantum mechanical phenomenon called electron degeneracy. About 95% of all the stars in our galaxy, including our own sun, will turn into a white dwarf. As the electrons in this very dense remainder of a star keep getting pushed to higher energy states, they generate an actual pressure that holds these stars together. Once this pressure can no longer balance self-attraction of the strong gravitational fields, a part or all of the white dwarf has to explode. A white dwarf by itself with no red giant star close to it is very stable and can live for hundreds of billions of years, much older than the entire known universe, which is only 13.8 billion years. When it no longer emits any heat at all, it will turn into a black dwarf.
The planets have spread out now and two of them have returned to grace our evening skies this month, Mercury and Venus. Look for Venus very low in our western sky right after sunset in Cancer the Crab, just to the left of Gemini. It will slowly get higher in our evening sky as the faster moving Venus is catching up with Earth in our orbits. Then look for Mercury about 10 degrees above and to the left of Venus toward Leo the Lion. Notice that a very thin waxing crescent moon will be directly above Mercury and Venus 20 minutes after sunset on July 7.
Saturn now rises at midnight in Aquarius. Through a telescope you will notice that its rings are getting very thin now, only tilted 2 degrees from edge-on. The rings will open up a little through the rest of this year, and then they will close up again to exactly edge-on in March of 2025. This last happened in 1996 and it happens every 29 years – the time it takes for Saturn to orbit the sun once. I remember seeing Saturn without its rings in 1996 when it looked more like Jupiter.
Mars rises next around 2 a.m. in Taurus the Bull. Notice that Mars will have almost the same brightness and orange color as Aldebaran, the brightest star in Taurus at 0.8 magnitude. Since Aldebaran marks the eye of Taurus in the Hyades star cluster which marks the face of Taurus, Taurus will appear to have two orange eyes for this whole month.
Then Jupiter is the next one to rise around 3:30 a.m., also in Taurus just to the left of Aldebaran. About one hour before sunrise on July 30, a waning crescent moon with earthshine will be visible just above Mars and Jupiter and just below the Pleiades open star cluster. You can also spot Uranus just to the right of the Pleiades and just above Jupiter and Mars with a pair of binoculars or a small telescope. Taurus is a busy region of the sky this month.
The largest and brightest asteroid, Ceres, will be easily visible in a pair of binoculars in Sagittarius near the center of our Milky Way galaxy all month long at 7.3 magnitude.
We will finally get the first good meteor shower since May on the last day of this month as the southern Delta Aquarid meteor shower peaks. You can expect 25 meteors per hour emanating from its radiant in Aquarius just below where Saturn is now located. Caused by Comet 96P/Machholz, this is only one of eight meteor showers related to this comet which has an orbital period of 5.3 years. This shower will be active from the middle of July into the middle of August. Also start looking for early Perseid meteors emanating from Perseus the hero in the northeastern sky near Cassiopeia. They will peak on Aug. 12.
There are two comets visible right now in a small telescope. Comet C/2023 (Tsuchinshan-ATLAS) is traveling westward through Leo this month. It is only shining at eighth magnitude now, but it is on track to becoming easily visible to the naked eye in October when it reemerges from behind the sun. The other one is ninth magnitude 13P/Olbers which is traveling through Lynx and Leo Minor.
JULY HIGHLIGHTS
July 1: The moon passes 4 degrees north of Mars this morning.
July 3: The moon passes 5 degrees north of Jupiter this morning.
July 5: Earth is at aphelion or farthest from the sun for the year at 94.5 million miles today. New moon is at 6:57 p.m.
July 7: The moon passes 3 degrees north of Mercury this evening.
July 11: Skylab, our first space station, re-entered our atmosphere in 1979.
July 13: First quarter moon is at 6:49 p.m. Jupiter passes 5 degrees north of Aldebaran this morning.
July 15: Mars passes less than one degree south of Uranus this morning.
July 21: Full moon is at 6:17 a.m. This is also known as the Hay, Buck, or Thunder Moon.
July 27: Last quarter moon is at 10:52 p.m.
July 30: The southern Delta Aquarid meteor shower peaks.
Bernie Reim of Wells is co-director of the Astronomical Society of Northern New England.
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