A little ramble through astronomy - The Dog Days of Summer

The “dog days of summer” is a phrase used to describe the hot and humid days of summer. It can be traced back thousands of years. It refers to the dates from July 3 through August 11, which is 20 days prior and 20 days after the star Sirius rises and falls in conjunction [sharing the same spot in our sky] with the sun. Sirius was known as the “Dog Star,” because it is the brightest star in the constellation Canis Major (Large Dog).

Sirius is the brightest star in the sky. The name Sirius comes from an ancient Greek word for “scorching” or “glowing.”

Since Sirius is in conjunction with the sun on July 23, the dog days of summer center around then. The dog days of summer fall between July 3 to August 11, and that’s when we have many of our warmest days in the Northern Hemisphere.

Now we often have very hot days before or after July 3 to August 11 however the legend of the dog days has survived.

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A little ramble through 19th century astronomy - comet 1840

 Nature March 16^th 1876

Comet 1840

In Astronomische Nachrichten, No. 2079, Dr Kowalczyk, of Warsaw, publishes I his investigation of a definitive orbit for the comet discovered at Berlin by prof Galle, the present Director pf the observatory at Breslau, on the 25^th January 1840.

This comet which was last observed at Kremsmunster on the 1^st April, had already been made the subject of extensive calculation b y Professors Plantamour and Loomis. The former in 1843, discussing his own series of careful observations taken at Geneva, found (Astron Nach, No. 476) that a parabolic orbit represented the comet’s course within the probable limits of error of observation; on including the series taken at Berlin he found the most probable orbit to be an ellipse, but of great eccentricity  to which little weight was considered to attach.

Loomis on his side, taking into account the effect of planetary perturbation  during the interval of the comet’ visibility, also found an ellipse, but with a mote moderate eccentricity, the period of revolution being about 2,400 years; the sum of the squares of  the errors of the ellipse is diminished to one third the amount with the best determinable parabola.

Loomis’s investigation will be found in the Transactions of the American Academy vol viii; his orbits are not in the included in the extensive collection in Dr Carl’s “Repertorium der Cometen-Astronomie”, a work which notwithstanding, its great utility  to the student of this branch of science, is yet not complete or free from numerical errors.

Kowalczyk starts with the parabolic elements obtained by Plantamour in 1843, comparing them with the whole course of observations. After introducing the corrections for aberrations and parallax , and the earth’s position from Leverrier’s tables, instead of those from the tables of Carlini used by previous computers and by the usual method of equations of conditions for ten normal places, he finally arrives at an elliptical orbit, very closely agreeing with observations, and showing a period of revolution of 3,789

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 years.

A little ramble through astronomy - Happy Aphelion Day July 6th

 On July 6, Earth will be at aphelion, the furthest point from the Sun it can reach on its yearly orbit. At aphelion, Earth will be 94,502,963 million miles (152, 087,778 million km) from the Sun. Earth was at perihelion, its closest point to the Sun, during January, when it was only 91,403 ,640 million miles (147,099,900 million km) away. 

The seasons are caused not by how close Earth is to the Sun, but by which hemisphere is tilted towards it. In July the northern hemisphere is tilted towards the Sun, so we have summer, while in January, when Earth is closest to the Sun, the northern hemisphere is tilted away from it and we have winter.

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Cooke Telescope Tales - Rothschild's observatory in 1889

 A report from 1889 says that Baron Albert von Rothschild’s observatory within the precincts of his palace is a bijou. A splendid equatorial by Thomas Cooke & Sons with a 9 inch aperture, to which the Baron has fitted notions of his own. Observations of double stars are made by him, and astronomers may in a year or two receive published results. Dr Palisa is the Baron’s court astronomer.

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A little ramble through Microscopium the Microscope

Another constellation introduced by Lacaille in the 1750s. This group represents another of the scientific instruments that Lacaille placed in the southern sky. Sadly as with so many of his new constellations Microscopium is little more than a filler between Sagittarius and Piscis Austrinus.

There are no bright stars in Microscopium. Even the mere hint of haze or moonlight means that the stars in Microscopium will not be seen. 

The brightest stars are gamma at magnitude 4.7, which lies at a distance of 225 light years and is a G class giant star.

Epsilon also has a magnitude of 4.7 and is an A class star lying 166 light years away.

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The Astronomy show on Drystone Radio

 Join me, Martin Lunn MBE every Monday evening from 7.00 pm-9.00 pm on the award-winning Astronomy Show on Drystone Radio, probably the only regular astronomy show on any radio station in the country. 

I will take my weekly look at the night sky and look at all the latest news in astronomy. There will be the astronomical anniversaries this week plus the latest news from the astronomical societies in the north of England.

The Astronomy Show every Monday evening only on Drystone Radio live online at www.drystoneradio.com DAB radio in Bradford and East Lancashire, or 102 and 103.5 FM and can also be heard later on the Drystone Radio Podcast.

 

Cooke Telescope Tales - occultation of Saturn in 1917

 Ernest Wunderlich at the Wyone Observatory, Port Hacking which is about 14 miles south of Sydney observed the occultation of Saturn by the moon on March 14^th 1917. The telescope used was a 4.5 inch Thomas Cooke & Sons telescope.  

The sky was at the commencement of occultation was, owing to slight haze, rather more luminous than usual, and this caused the loss of the “inner edge of ring” and “first limb” of the ball at ingress. At egress the definition was all that could be desired, but the first edge of ring was decidedly outside the Moon’s illuminated edge before it was noticed, and thus was “lost”.

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