The Delta Aquarid meteor shower should be at its peak in the nights of July 29/30 and 30/31. But it is a low, soft “peak.”
See the end note about enlarging illustrations.
Meteors are streaks of light made by small solid particles plunging into the upper atmosphere; annual showers happen when Earth in its nearly circular orbit passes through streams of particles keeping approximately to the orbits of comets from which they have detached. The Delta Aquarid stream, unlike for instance that which produces the Lyrids of April, is very broad and diffuse. Broad, diffuse streams that may overlap each other or divide into sub-streams are problematic for scientists to analyze, and there has been a history of theories as to this one and its relatives (more about this in the paragraph on page 134 of Astronomical Calendar 2024).
The shower is named for its radiant: the small area from which the meteors appear to fly out to any part of the sky. Delta Aquarii is one of the stars imagined as the cascade poured from the jar of Aquarius the “water-carrier,” so it is in the part of the constellation that is south of the ecliptic.
Because the stream is broad, its duration of activity is long, from about July 12 to August 23; on any of these nights, a meteor may appear that can be traced back to the radiant.
The position of the radiant drifts slightly eastward from day to day over the period of activity, because of Earth’s motion around its curving orbit. This is what is indicated by the arrow through the radiant in our sky scene.
Around the peak dates, the zenithal hourly rate (ZHR) is 25. This is the estimated number that a single alert observer might count if the sky is clear and dark and the radiant is overhead – ideal conditions which could be met only in places such as northern Australia. You are more likely to notice 5 an hour.
Our sky scene for a USA location shows the radiant coming up over the horizon toward midnight. It will continue to climb, parallel to the celestial equator, till about 2 AM. The higher it is, the more meteor tracks are likely to be above the horizon.
Moonlight, this year, does not interfere. The Moon will not rise until shortly before the Sun does.
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ILLUSTRATIONS in these posts are made with precision but have to be inserted in another format. You may be able to enlarge them on your monitor.
One way: right-click, and choose ”View image” or ”Open image in new tab”, then enlarge. Or choose ”Copy image”, then put it on your desktop, then open it. On an iPad or phone, use the finger gesture that enlarges (spreading with two fingers, or tapping and dragging with three fingers). Other methods have been suggested, such as dragging the image to the desktop and opening it in other ways.
I understand that meteor shower ZHR data is iffy and year-to-year variable (some showers more than others) but it would be nice to have some running radar-based meteor data for near shower dates (or, wow, the whole year!). This would back up verbal descriptions of shower peak width and intensity with something graphic to work with. Any prospect of that?
The place to find such data is probably the website of the IMO, International Meteor Orgnization.
Hello Guy,
Just curious – where is the celestial north pole of Uranus?
All the other planets, Earth included, have their celestial north poles in some fair proximity to our own ecliptic north pole.
However, Uranus, tilted over by 98 degrees to its orbit, must have its axial north pole pointing somewhere in or just south of our Zodiac.
But where?
Kenneth A. Heisler
Kenneth, I’m going to nr lazy and quote the whole of my entry for “north” in Albedo to ZodiacL
north<$> (from a Germanic base that has not been traced back to Indo-European; may be related to Greek nerteros<$>, “lower, infernal”, perhaps because the Sun is highest in the south): the direction away from the mid-day Sun (as seen from regions such as Europe on the northern part of the Earth). This definition is circular, since it contains “north”. A more impartial definition is that, as you face forward in the Earth’s rotation (toward east, the direction from which the Sun and stars rise), north is the direction to the left. If the Earth were a wheel, north would be the hub on the left. If you were hovering in space above the north pole, looking down you would see the Earth rotate counter-clockwise. If you hold out your right<$> hand with fingers curved, and thumb pointing up, the fingers represent the direction of rotation and the thumb represents the north<$> pole.
And in general the whole solar system rotates in the same sense (sense<$> has a technical meaning “direction of rotation”), counterclockwise as seen from the north: the individual bodies mostly rotate that way, and mostly revolve that way around the Sun. However, some do not. Four of Jupiter’s outer satellites (Ananke, Carme, Pasiphae, Sinope), one of Saturn’s (Phoebe), and one of Neptune’s (Triton) revolve in the retrograde<$> (westward) direction around their planets; and long-period comets travel in all directions around the Sun, half of them retrograde. As for retrograde rotation, Venus has it, and so must many of the small bodies: that is, spinning westward, or clockwise as seen from the northern part of our sky. The result is that in these cases there is a question as to which of two opposite directions is to be called “north”: the direction that is to the left when you face forward in the direction of rotation; or the direction that is in the northern hemisphere of the Earth’s sky. The answer is, roughly, the latter, according to the 1970 decision of the International Astronomical Union: the north pole of a planet is defined as the rotation axis that lies on the north side of the invariant plane<$> of the solar system, which is almost the same as the ecliptic plane. Jean Meeus, More Mathamtical Astronomy Morsels<$>, p. 299, gives strong objections to this decision.
The major borderline case is the planet Uranus, which rotates on its side in relation to the rest of the solar system. One of its poles points at the star Eta Ophiuchi (Sabik), 15#d south of the Earth’s equatorial plane, but 8#d north of the ecliptic: thus this pole has to count as the north pole. But Uranus rotates clockwise around it (that is, the rotation would be clockwise if viewed from above this pole); therefore, Uranus has to count as having retrograde rotation. If Uranus were to be “stood up”, so that this pole pointed parallel with the Earth’s, we would see Uranus spinning backwards compared with the Earth.
We will presumably discover that about half of the other stars and their planets in the galaxy rotate and revolve in retrograde directions – or perhaps more than half. For the galaxy itself rotates in a retrograde direction (as referred to the solar system): the galactic pole that is in the northern half of our sky (in the constellation Coma) is called the north galactic pole, but viewed from that pole the galaxy is rotating clockwise. If the galaxy were a wheel rolling forward, the pole in Coma would be the hub on the right.
Compare the discussion under east<$>.