] Starry Night Times
Simulation Curriculum

For education orders please call 1-877-290-8256.

Welcome to the August Fourth Week Featured Article!

Who Discovered Neptune?

Geoff Gaherty, Starry Night Education

This week, on Friday August 29, Neptune will be in opposition to the Sun: exactly opposite the Sun in Earth’s sky.

Neptune was supposedly discovered in 1846 by Johann Gottfried Galle using calculations by Urbain Le Verrier and John Couch Adams, making it a joint British-French-German discovery. Yet the first man to observe Neptune was none of these, but instead the Italian astronomer Galileo Galilei.

While sketching the moons of Jupiter with his newly discovered telescope, Galileo twice drew Neptune, which happened to be in conjunction with Jupiter in early 1613. It’s usually said that Galileo mistook Neptune for a star because of its slow movement.

Recently , David Jamieson of the University of Melbourne has argued that Galileo did indeed see Neptune move and realized it was a planet. Jamieson thinks Galileo announced this in an anagram, but it as suppressed by the Catholic Church. Conspiracy theories are nothing new.

It’s interesting to examine historic observations like Galileo’s to see what was actually observed. Modern planetarium programs allow us to do this

Here is Galileo’s sketch from 1612 December 27/28 On the night of 1612 December 27/28, Galileo sketched the positions of Jupiter’s moons, and included a background “star” which turned out to be the planet Neptune.
On the night of 1612 December 27/28, Galileo sketched the positions of Jupiter’s moons, and included a background "star" which turned out to be the planet Neptune.

and Starry Night’s rendition of the same event (at 2 a.m. on December 28) This view from Starry Night demonstrates the accuracy of Galileo’s observation. Credit: Starry Night Software
This view from Starry Night demonstrates the accuracy of Galileo’s observation. Credit: Starry Night Software

Jupiter is framed by Ganymede on the left and Europa on the right, with Callisto a little further to the right. Neptune is on the left, and slightly north of Jupiter. Io was probably too close to Jupiter to be resolved at the low magnification Galileo used.

Just over a month later, Galileo sketched the moons again On 1613 January 28/29, Galileo again sketched Jupiter’s moons, and again included the planet Neptune.
On 1613 January 28/29, Galileo again sketched Jupiter’s moons, and again included the planet Neptune.

Here is Starry Night’s version. Again Starry Night shows how accurate Galileo’s observations were. Credit: Starry Night Software.
Again Starry Night shows how accurate Galileo’ s observations were. Credit: Starry Night software.

All four moons are off to Jupiter’s right, and Galileo has portrayed their positions accurately. Neptune is again to Jupiter’s left, but now south of Jupiter.

What happened between these two sketches is truly remarkable. When the first sketch was made, Neptune was moving from left to right relative to Jupiter. On 1613 January 3/4 Neptune actually passed behind Jupiter, an extremely rare planetary occultation. Had Galileo observed just before dawn on the morning of the 4th, he would have seen Neptune emerging from behind the dark limb of Jupiter.
On the night of 1613 January 3/4, Jupiter actually occulted Neptune. Credit: Starry Night Software.
On the night of 1613 January 3/4, Jupiter actually occulted Neptune. Credit: Starry Night Software.

Neptune was stationary relative to Jupiter on January 13, and then started moving from right to left, passing Jupiter again on January 23, ending up again to the left of Jupiter for Galileo’s second observation on January 28/29.

Galileo’s primitive telescope was capable of only about 30 times magnification. Neptune would have looked to him like a star, just as it does in small telescopes today. It takes a very large telescope, and very good conditions to see anything like the view in Starry Night. I once had the opportunity to observe Neptune through the largest telescope in Canada, the 74-inch reflector at the David Dunlap Observatory north of Toronto. Even with this telescope, Neptune was a featureless blue disk.


gifspacer gifspacer gifspacer
Feedback
gifspacer

   
Send us your feedback

Do you have a question, comment, suggestion or article idea to pass along to Starry Night® Times?

Click here to get in touch with us.
   

gifspacer
Feedback
Follow Us on Twitter
Educational Inquiries and Sales

   
Follow us at
• twitter.com/starrynightedu
   

Educational Inquiries and Sales
Educational Inquiries and Sales
gifspacer gifspacer gifspacer
Educational Inquiries and Sales
Educational Inquiries and Sales

   
Educational Inquiries and Sales

Please contact us for all education inquiries. EDUCATION ORDERS 1-877-290-8256
   

Educational Inquiries and Sales
Educational Inquiries and Sales
gifspacer gifspacer gifspacer
Subscriptions
gifspacer

   
Starry Night®
is the world's leading line of educational astronomy software and DVDs. Visit store.simulationcurriculum.com to see all the great products we offer for everyone from novice to experienced astronomers.

You have received this e-mail as a user of Starry Night® or as a registrant at starrynighteducation.com.

Starry Night® is a division of Simulation Curriculum Corp.

Simulation Curriculum Corp.
Starry Night® Education

11900 Wayzata Blvd.
Suite 126
Minnetonka, MN 55305
Tel: 1-866-688-4175
   

gifspacer
Subs

© 2016 Simulation Curriculum Corp. All Rights Reserved.