Help needed

I read on the Internet about the discovery of Saturn's rings over the last four hundred years. I found it interesting and confusing that the verb tense in the article varies between the past simple and the present simple. I would be very happy if you could tell me why. Here are some of the sentences from the article:

1600- galileo Galilei -becomes- the first to observe Saturn's rings with his 20-power telescope. He -thought- the rings -were- "handles" or large moons on either side of the planet. He said".....".
1612- Galileo -was astounded- then he -found- that the rings he first observed a couple of years earler had now disappeared. He wrote"....".
1615- Galileo now -observes- the rings as two half ellipses.
1655- Christtann Huygens -proposes- that Saturn -was surrounded- by a solid ring. ...Using a 50 power refractor that he designed himself, Huygens also -discovers- .......
1789- William Herschel -suggests- that Saturn i-s surrounded- by two solid rings.
1790- William Herschel -is- able to determine the rotation period ...
1850- ...... George bond -condludes- that a systemof narrow solid rings -could- not be stable and that Saturn's rings -had -to be fluid.
1852- Several observers -notice- that.... This observation -made- it difficult to defend the theory that the rings were solid.
1862-1862- The dark unlit side of Saturn's rings -was observed- by Fames Carpenter,.......
1876- Spectacular white spots -are observed- on saturn by Asaph Hall.
1907- 1908- Observations during the 1907-1908 ring plane crossing -led- to an estimate for the ring's thickness of no more than 15 km.
1923- B. Lyot -was able- to detect the polarization of light scattered by Saturn's rings.
1977- Voyger 1 and Voyger 2 -are launched- to encounter Saturn in 1980 and 1981.

There are also some tense inconsistencies in my opinion, maybe I am wrong.
* 1655- Christtann Huygens -proposes- that Saturn -was surrounded- by a solid ring. ...Using a 50 power refractor that he designed himself, Huygens also -discovers- .......
while in
1789- William Herschel -suggests- that Saturn -is surrounded- by two solid rings.
1850- ...... George bond -concludes- that a systemof narrow solid rings -could- not be stable and that Saturn's rings -had -to be fluid.

Huygens proposes that Saturn was surrounded by, but
William Herschel suggests that Saturn is surrounded by
George Bond concludes that a system of narrow solid rings could not be stable and had to be fluid.

1862-1862- The dark unlit side of Saturn's rings -was observed- by Fames Carpenter,.......
1876- Spectacular white spots -are observed- on saturn by Asaph Hall.

The dark unlit side of Saturn's rings was observed by but
White spots are observed by
* 1923- B. Lyot -was able- to detect the polarization of light scattered by Saturn's rings.
1790- William Herschel -is- able to determine the rotation period ...
B. Lyot was able to but
William Herschel is able to

If you would like to refer to the article, the site is http://www.ssd.rl.ac.uk/news/cassini/sat.html

This is a long post. Thank you for taking time to help me.