Auction for collection of Albert Einstein's letters and postcards ends next week

The collection of items belonged to Albert Einstein's sister, Maja Einstein.

Online bidding for a collection of Einstein's letters, photographs and postcards will end on Wednesday.

The Christie’s auction, titled “Einstein and Family: Letters and Portraits,” features items drawn from the personal collection of Einstein's younger sister, Maja Einstein, and her husband, Paul Winteler.

The material in the collection are mostly unpublished and "shed new light on the extraordinary life and complex character of the 20th century's most famous scientist," a Christie's description of the sale reads.

Among the items are a never-before-published photo of Einstein at 5 years old -- expected to garner bids up to $8,000 -- and the only surviving letter that Einstein wrote to his father.

Einstein had just completed his first year at Zurich Polytechnic at the time.

A photo of Einstein and his sister circa 1893 is expected to sell for up to $2,000. It was taken in Munich, where Einstein's family lived until 1894, after his father and uncle's electrical business began to fail, according to Christie's.

Maja was one of Einstein's closest confidantes, the National Geographic reported.

In a postcard Einstein wrote to his mother, Pauline Einstein, in September 1900, Einstein sent his greetings from a trip to Venice with her father, where he enjoyed "sea-bathing" and "music in the most beautiful sunshine," according to Christie's.

Bidding on the Christie's website ends Wednesday.