Introduction to Hawaii

http://teachingtravel.com/map-of-hawaii-islands.html

The eight main islands of Hawaii, from northwest to southeast:

Niihau
Kauai
Oahu
Molokai
Lanai
Kahoolawe
Maui
The island of Hawaii (also referred to as "The Big Island")

These eight "main" islands anchor the southern end of the Hawaiian archipelago (made up of hundreds of islands which stretch over 1,500 miles). While most of the islands in the archipelago are part of the state, we usually think only of the eight main ones when we say Hawaii.

Which islands to visit?

Niihau: The island is owned by the Robinson family. Tours to the island are available now. In the past there was no public access. The island is the last community of pure blooded Hawaiians. It's nicknamed "The Forbidden Island."
Kauai: Rural, rustic, lush. Sparsely populated. Good for hiking and outdoor activities.
Oahu: The capitol, Honolulu, is located on Oahu. The most densely populated island, yet still rural in the north side of the island. A bit of both city and rustic life on this island.
Molokai: A largely un-touristy island. Sparsely populated.
Lanai. This small island is owned by Larry Ellison of Oracle. It has two luxury hotels, one on the beach and the other inland which reminds me of a hunting lodge. There is also an old time plantation inn. If you want a private luxurious place to relax away from the maddening crowd, Lanai may be for you. The scones at the airport and the bakery are delicious. (Caveat, don't know if they're still available.)
Kahoolawe. This small island was used by the military for target practice. Nobody goes there except maybe Hawaiian activists who used to go to protest the bombing and to protect the land.
Maui. It's the most commercial island after Oahu, and the hippest. Lots of rock stars have homes there. George Harrison had a home in the remote area of Hana. Note: if you get carsick, don't go to Hana, unless you can drive all the way.
The island of Hawaii, "The Big Island," is the home to the active volcano Kilauea which has been quietly erupting since 1983. You can find Mauna Kea, the tallest mountain in the world when measured from its base, on this island, as well as numerous observatories which find the high clear altitude away from city lights perfect for space observation. The Kona side of the island produces the famous Kona Coffee. In this sunnier side of the island, luxurious resorts like the Four Seasons Resort Hualalai dot the outskirts of the town proper. The county seat of Hilo is located on the rainy side of the island, close to the Volcanoes National Park where for a park entrance fee one can observe the bubbling lava cauldron of Kilauea. There's a hotel on the rim of the cauldron for a special experience. Cabins and campgrounds are also available.

Here's a link to live cams for observatories on Mauna Kea: http://mkwc.ifa.hawaii.edu/current/cams/index.cgi
Enjoy.

I'll delve more specifically into each island later.

Aloha and Mahalo.

This map of the Hawaiian archipelago puts the eight main islands in perspective:

https://fia.umd.edu/answer-pulling-together-information-about-the-geography-of-hawaii/